The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
A close-in giant planet escapes engulfment by its starSérgio Sacani
When main-sequence stars expand into red giants, they are expected to engulf closein planets1–5
. Until now, the absence of planets with short orbital periods around
post-expansion, core-helium-burning red giants6–8
has been interpreted as evidence
that short-period planets around Sun-like stars do not survive the giant expansion
phase of their host stars9
. Here we present the discovery that the giant planet 8 Ursae
Minoris b10 orbits a core-helium-burning red giant. At a distance of only 0.5 au from its
host star, the planet would have been engulfed by its host star, which is predicted by
standard single-star evolution to have previously expanded to a radius of 0.7 au. Given
the brief lifetime of helium-burning giants, the nearly circular orbit of the planet is
challenging to reconcile with scenarios in which the planet survives by having a distant
orbit initially. Instead, the planet may have avoided engulfment through a stellar
merger that either altered the evolution of the host star or produced 8 Ursae Minoris b
as a second-generation planet11. This system shows that core-helium-burning red
giants can harbour close planets and provides evidence for the role of non-canonical
stellar evolution in the extended survival of late-stage exoplanetary systems.
Remote detection of a lunar granitic batholith at Compton–BelkovichSérgio Sacani
Granites are nearly absent in the Solar System outside of Earth. Achieving granitic
compositions in magmatic systems requires multi-stage melting and fractionation,
which also increases the concentration of radiogenic elements1
. Abundant water and
plate tectonics facilitate these processes on Earth, aiding in remelting. Although these
drivers are absent on the Moon, small granite samples have been found, but details
of their origin and the scale of systems they represent are unknown2
. Here we report
microwave-wavelength measurements of an anomalously hot geothermal source that
is best explained by the presence of an approximately 50-kilometre-diameter granitic
system below the thorium-rich farside feature known as Compton–Belkovich. Passive
microwave radiometry is sensitive to the integrated thermal gradient to several
wavelengths depth. The 3–37-gigahertz antenna temperatures of the Chang’e-1 and
Chang’e-2 microwave instruments allow us to measure a peak heat fux of about
180 milliwatts per square metre, which is about 20 times higher than that of the
average lunar highlands3,4
. The surprising magnitude and geographic extent of this
feature imply an Earth-like, evolved granitic system larger than believed possible on
the Moon, especially outside of the Procellarum region5
. Furthermore, these methods
are generalizable: similar uses of passive radiometric data could vastly expand our
knowledge of geothermal processes on the Moon and other planetary bodies.
This study uses asteroseismology to reveal fast core rotation in red giant stars, finding that the cores rotate at least 10 times faster than the surface by analyzing rotational splitting of mixed modes. Mixed modes that probe the core show larger rotational splitting than modes dominated by the outer layers, indicating non-rigid rotation that increases towards the stellar interior. Models are able to reproduce the observations, confirming theoretical predictions of a steep rotational gradient within red giant cores.
A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curveSérgio Sacani
There are no planets intermediate in size between Earth and Neptune in our Solar System, yet these objects are found around a
substantial fraction of other stars [1]. Population statistics show that
close-in planets in this size range bifurcate into two classes based
on their radii [2, 3]. It is hypothesized that the group with larger
radii (referred to as “sub-Neptunes”) is distinguished by having
hydrogen-dominated atmospheres that are a few percent of the total
mass of the planets [4]. GJ 1214b is an archetype sub-Neptune that
has been observed extensively using transmission spectroscopy to
test this hypothesis [5–14]. However, the measured spectra are featureless, and thus inconclusive, due to the presence of high-altitude
ACCELERATED ARTICLE PREVIEW
Springer Nature 2021 LATEX template
GJ 1214b Phase Curve 3
aerosols in the planet’s atmosphere. Here we report a spectroscopic thermal phase curve of GJ 1214b obtained with JWST in the
mid-infrared. The dayside and nightside spectra (average brightness
temperatures of 553 ± 9 and 437 ± 19 K, respectively) each show > 3σ
evidence of absorption features, with H2O as the most likely cause in
both. The measured global thermal emission implies that GJ 1214b’s
Bond albedo is 0.51 ± 0.06. Comparison between the spectroscopic
phase curve data and three-dimensional models of GJ 1214b reveal
a planet with a high metallicity atmosphere blanketed by a thick
and highly reflective layer of clouds or haze.
Computation of Lyapunov Exponent for Characterizing the Dynamics of Earthquakeijrap
Earthquakes forecasting and prediction is a global challenge, several precursors and methods of
earthquake prediction have been proposed, but lack consistency and are not reliable for prediction hence
occurrence of earthquakes is sometimes assumed to be random. This study was designed to investigate and
characterise the occurrence of earthquakes using chaos theory. The Lyapunov Exponent and its spectrum
were obtained from earthquake data using modified two dimensional system method from Sprott’s
procedures. The results show that the values of the Lyapunov exponent were positive but the magnitude
varies for all regions considered and the Lyapunov exponent spectrum exhibit an asymptotic behaviour in
all the regions.This study showed that although seismicity exhibit apparent randomness but earthquake
occurrence is not stochastic but a non-linear deterministic dynamical process.
Long term modulation of cosmic ray intensity in statistical relation with cor...Alexander Decker
This document summarizes a study that analyzed the statistical correlation between long-term cosmic ray intensity and solar activity parameters like coronal mass ejections (CMEs) and solar flare index numbers between 1997 and 2010. The study found a negative correlation between cosmic ray intensity and both CMEs (correlation coefficient of -0.83) and solar flare index (-0.70), indicating that cosmic ray intensity is inversely related to solar activity levels. Figures 1 and 2 show scatter plots illustrating these negative correlations between cosmic ray intensity and the respective solar parameters.
A high-mass X-ray binary descended from an ultra-stripped supernovaSérgio Sacani
Ultra-stripped supernovae are diferent from other terminal explosions of massive
stars, as they show little or no ejecta from the actual supernova event1,2
. They are
thought to occur in massive binary systems after the exploding star has lost its surface
through interactions with its companion2
. Such supernovae produce little to no kick,
leading to the formation of a neutron star without loss of the binary companion,
which itself may also evolve into another neutron star2
. Here we show that a recently
discovered high-mass X-ray binary, CPD −29 2176 (CD −29 5159; SGR 0755-2933)3–6
, has
an evolutionary history that shows the neutron star component formed during an
ultra-stripped supernova. The binary has orbital elements that are similar both in
period and in eccentricity to 1 of 14 Be X-ray binaries that have known orbital periods
and eccentricities7
. The identifcation of the progenitors systems for ultra-stripped
supernovae is necessary as their evolution pathways lead to the formation of binary
neutron star systems. Binary neutron stars, such as the system that produced the
kilonova GW170817 that was observed with both electromagnetic and gravitational
energy8
, are known to produce a large quantity of heavy elements
Observational evidence from supernovae for an accelerating universe and a cos...Sérgio Sacani
The document presents observations of 10 type Ia supernovae (SNe Ia) with redshifts between 0.16 and 0.62. Combined with previous data from the team and others, the distances to the 16 high-redshift SNe Ia are on average 10-15% farther than expected in a low-mass density universe without a cosmological constant. Different analysis methods find evidence favoring an expanding universe with a positive cosmological constant and acceleration of the expansion. The data are consistent with an accelerating universe and cosmological constant at a statistical significance of 2.8-9 sigma depending on the method and assumptions.
A close-in giant planet escapes engulfment by its starSérgio Sacani
When main-sequence stars expand into red giants, they are expected to engulf closein planets1–5
. Until now, the absence of planets with short orbital periods around
post-expansion, core-helium-burning red giants6–8
has been interpreted as evidence
that short-period planets around Sun-like stars do not survive the giant expansion
phase of their host stars9
. Here we present the discovery that the giant planet 8 Ursae
Minoris b10 orbits a core-helium-burning red giant. At a distance of only 0.5 au from its
host star, the planet would have been engulfed by its host star, which is predicted by
standard single-star evolution to have previously expanded to a radius of 0.7 au. Given
the brief lifetime of helium-burning giants, the nearly circular orbit of the planet is
challenging to reconcile with scenarios in which the planet survives by having a distant
orbit initially. Instead, the planet may have avoided engulfment through a stellar
merger that either altered the evolution of the host star or produced 8 Ursae Minoris b
as a second-generation planet11. This system shows that core-helium-burning red
giants can harbour close planets and provides evidence for the role of non-canonical
stellar evolution in the extended survival of late-stage exoplanetary systems.
Remote detection of a lunar granitic batholith at Compton–BelkovichSérgio Sacani
Granites are nearly absent in the Solar System outside of Earth. Achieving granitic
compositions in magmatic systems requires multi-stage melting and fractionation,
which also increases the concentration of radiogenic elements1
. Abundant water and
plate tectonics facilitate these processes on Earth, aiding in remelting. Although these
drivers are absent on the Moon, small granite samples have been found, but details
of their origin and the scale of systems they represent are unknown2
. Here we report
microwave-wavelength measurements of an anomalously hot geothermal source that
is best explained by the presence of an approximately 50-kilometre-diameter granitic
system below the thorium-rich farside feature known as Compton–Belkovich. Passive
microwave radiometry is sensitive to the integrated thermal gradient to several
wavelengths depth. The 3–37-gigahertz antenna temperatures of the Chang’e-1 and
Chang’e-2 microwave instruments allow us to measure a peak heat fux of about
180 milliwatts per square metre, which is about 20 times higher than that of the
average lunar highlands3,4
. The surprising magnitude and geographic extent of this
feature imply an Earth-like, evolved granitic system larger than believed possible on
the Moon, especially outside of the Procellarum region5
. Furthermore, these methods
are generalizable: similar uses of passive radiometric data could vastly expand our
knowledge of geothermal processes on the Moon and other planetary bodies.
This study uses asteroseismology to reveal fast core rotation in red giant stars, finding that the cores rotate at least 10 times faster than the surface by analyzing rotational splitting of mixed modes. Mixed modes that probe the core show larger rotational splitting than modes dominated by the outer layers, indicating non-rigid rotation that increases towards the stellar interior. Models are able to reproduce the observations, confirming theoretical predictions of a steep rotational gradient within red giant cores.
A reflective, metal-rich atmosphere for GJ 1214b from its JWST phase curveSérgio Sacani
There are no planets intermediate in size between Earth and Neptune in our Solar System, yet these objects are found around a
substantial fraction of other stars [1]. Population statistics show that
close-in planets in this size range bifurcate into two classes based
on their radii [2, 3]. It is hypothesized that the group with larger
radii (referred to as “sub-Neptunes”) is distinguished by having
hydrogen-dominated atmospheres that are a few percent of the total
mass of the planets [4]. GJ 1214b is an archetype sub-Neptune that
has been observed extensively using transmission spectroscopy to
test this hypothesis [5–14]. However, the measured spectra are featureless, and thus inconclusive, due to the presence of high-altitude
ACCELERATED ARTICLE PREVIEW
Springer Nature 2021 LATEX template
GJ 1214b Phase Curve 3
aerosols in the planet’s atmosphere. Here we report a spectroscopic thermal phase curve of GJ 1214b obtained with JWST in the
mid-infrared. The dayside and nightside spectra (average brightness
temperatures of 553 ± 9 and 437 ± 19 K, respectively) each show > 3σ
evidence of absorption features, with H2O as the most likely cause in
both. The measured global thermal emission implies that GJ 1214b’s
Bond albedo is 0.51 ± 0.06. Comparison between the spectroscopic
phase curve data and three-dimensional models of GJ 1214b reveal
a planet with a high metallicity atmosphere blanketed by a thick
and highly reflective layer of clouds or haze.
Computation of Lyapunov Exponent for Characterizing the Dynamics of Earthquakeijrap
Earthquakes forecasting and prediction is a global challenge, several precursors and methods of
earthquake prediction have been proposed, but lack consistency and are not reliable for prediction hence
occurrence of earthquakes is sometimes assumed to be random. This study was designed to investigate and
characterise the occurrence of earthquakes using chaos theory. The Lyapunov Exponent and its spectrum
were obtained from earthquake data using modified two dimensional system method from Sprott’s
procedures. The results show that the values of the Lyapunov exponent were positive but the magnitude
varies for all regions considered and the Lyapunov exponent spectrum exhibit an asymptotic behaviour in
all the regions.This study showed that although seismicity exhibit apparent randomness but earthquake
occurrence is not stochastic but a non-linear deterministic dynamical process.
Long term modulation of cosmic ray intensity in statistical relation with cor...Alexander Decker
This document summarizes a study that analyzed the statistical correlation between long-term cosmic ray intensity and solar activity parameters like coronal mass ejections (CMEs) and solar flare index numbers between 1997 and 2010. The study found a negative correlation between cosmic ray intensity and both CMEs (correlation coefficient of -0.83) and solar flare index (-0.70), indicating that cosmic ray intensity is inversely related to solar activity levels. Figures 1 and 2 show scatter plots illustrating these negative correlations between cosmic ray intensity and the respective solar parameters.
A high-mass X-ray binary descended from an ultra-stripped supernovaSérgio Sacani
Ultra-stripped supernovae are diferent from other terminal explosions of massive
stars, as they show little or no ejecta from the actual supernova event1,2
. They are
thought to occur in massive binary systems after the exploding star has lost its surface
through interactions with its companion2
. Such supernovae produce little to no kick,
leading to the formation of a neutron star without loss of the binary companion,
which itself may also evolve into another neutron star2
. Here we show that a recently
discovered high-mass X-ray binary, CPD −29 2176 (CD −29 5159; SGR 0755-2933)3–6
, has
an evolutionary history that shows the neutron star component formed during an
ultra-stripped supernova. The binary has orbital elements that are similar both in
period and in eccentricity to 1 of 14 Be X-ray binaries that have known orbital periods
and eccentricities7
. The identifcation of the progenitors systems for ultra-stripped
supernovae is necessary as their evolution pathways lead to the formation of binary
neutron star systems. Binary neutron stars, such as the system that produced the
kilonova GW170817 that was observed with both electromagnetic and gravitational
energy8
, are known to produce a large quantity of heavy elements
Observational evidence from supernovae for an accelerating universe and a cos...Sérgio Sacani
The document presents observations of 10 type Ia supernovae (SNe Ia) with redshifts between 0.16 and 0.62. Combined with previous data from the team and others, the distances to the 16 high-redshift SNe Ia are on average 10-15% farther than expected in a low-mass density universe without a cosmological constant. Different analysis methods find evidence favoring an expanding universe with a positive cosmological constant and acceleration of the expansion. The data are consistent with an accelerating universe and cosmological constant at a statistical significance of 2.8-9 sigma depending on the method and assumptions.
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
A rock composition_for_earth_sized_exoplanetsSérgio Sacani
1) Researchers measured the mass of Kepler-78b, an Earth-sized exoplanet orbiting its host star every 8.5 hours, to be 1.69 ± 0.41 M⊕ using Doppler spectroscopy of the star's radial velocity variations.
2) Given the planet's radius of 1.20 ± 0.09 R⊕, its mean density of 5.3 ± 1.8 g/cm3 is similar to Earth's, suggesting a rocky composition of iron and rock.
3) Kepler-78b is the smallest exoplanet yet characterized with both an accurate mass and radius measurement, extending measurements of planetary composition into the size range of Earth and Venus.
1) PSR J033711715 is a millisecond pulsar discovered to be in a hierarchical triple system with two white dwarf companions, making it the first known millisecond pulsar triple system.
2) Precise timing observations using multiple radio telescopes determined the masses of the pulsar (1.4378 solar masses), inner white dwarf companion (0.19751 solar masses), and outer white dwarf companion (0.4101 solar masses) to high precision.
3) The unexpectedly coplanar and nearly circular orbits of the system indicate an exotic evolutionary history and provide an opportunity to test theories of general relativity by studying the interactions between the bodies.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
Is the atmosphere of the ultra-hot Jupiter WASP-121 b variable?Sérgio Sacani
We present a comprehensive analysis of the Hubble Space Telescope observations of the atmosphere
of WASP-121 b, a ultra-hot Jupiter. After reducing the transit, eclipse, and phase-curve observations
with a uniform methodology and addressing the biases from instrument systematics, sophisticated
atmospheric retrievals are used to extract robust constraints on the thermal structure, chemistry, and
cloud properties of the atmosphere. Our analysis shows that the observations are consistent with a
strong thermal inversion beginning at ∼104 Pa on the dayside, solar to subsolar metallicity Z (i.e.,
−0.77 < log(Z) < 0.05), and super-solar C/O ratio (i.e., 0.59 < C/O < 0.87). More importantly,
utilizing the high signal-to-noise ratio and repeated observations of the planet, we identify the following
unambiguous time-varying signals in the data: i) a shift of the putative hotspot offset between the
two phase-curves and ii) varying spectral signatures in the transits and eclipses. By simulating the
global dynamics of WASP-121 b atmosphere at high-resolution, we show that the identified signals are
consistent with quasi-periodic weather patterns, hence atmospheric variability, with signatures at the
level probed by the observations (∼5% to ∼10%) that change on a timescale of ∼5 planet days; in
the simulations, the weather patterns arise from the formation and movement of storms and fronts,
causing hot (as well as cold) patches of atmosphere to deform, separate, and mix in time.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Evidence for baryon acoustic oscillations from galaxy–ellipticity correlationsSérgio Sacani
The baryon acoustic oscillation feature in the clustering of galaxies
or quasars provides a ‘standard ruler’ for distance measurements in
cosmology. In this work, we report a 2–3σ signal of the baryon acoustic
oscillation dip feature in the galaxy density–ellipticity cross-correlation
functions using the spectroscopic sample of the Baryon Oscillation
Spectroscopic Survey CMASS, combined with the deep Dark Energy
Spectroscopic Instrument Legacy Imaging Surveys for precise galaxy shape
measurements. We measure the galaxy–ellipticity correlation functions and
model them using the linear alignment model. We constrain the distance
DV/rd to redshift 0.57 to a precision of 3–5%, depending on the details of
modelling. The galaxy–ellipticity measurement reduces the uncertainty
of distance measurement by ~10% on top of that derived from the galaxy–
galaxy correlation. More importantly, for future large and deep galaxy
surveys, the independent galaxy–ellipticity measurements can help sort out
the systematics in the baryon acoustic oscillation studies.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
The tumbling rotational state of 1I/‘OumuamuaSérgio Sacani
The discovery1
of 1I/2017 U1 (1I/‘Oumuamua) has provided
the first glimpse of a planetesimal born in another planetary
system. This interloper exhibits a variable colour within a
range that is broadly consistent with local small bodies, such
as the P- and D-type asteroids, Jupiter Trojans and dynamically
excited Kuiper belt objects2–7
. 1I/‘Oumuamua appears
unusually elongated in shape, with an axial ratio exceeding
5:1 (refs 1,4,5,8). Rotation period estimates are inconsistent
and varied, with reported values between 6.9 and 8.3 h
(refs 4–6,9). Here, we analyse all the available optical photometry
data reported to date. No single rotation period can explain
the exhibited brightness variations. Rather, 1I/‘Oumuamua
appears to be in an excited rotational state undergoing nonprincipal
axis rotation, or tumbling. A satisfactory solution
has apparent lightcurve frequencies of 0.135 and 0.126 h−1
and
implies a longest-to-shortest axis ratio of ≳5:1, although the
available data are insufficient to uniquely constrain the true
frequencies and shape. Assuming a body that responds to
non-principal axis rotation in a similar manner to Solar System
asteroids and comets, the timescale to damp 1I/‘Oumuamua’s
tumbling is at least one billion years. 1I/‘Oumuamua was
probably set tumbling within its parent planetary system and
will remain tumbling well after it has left ours.
This research news article discusses two studies that propose different models to explain an unusual gamma-ray burst (GRB) called the "Christmas burst" that occurred on Christmas Day in 2010.
One study suggests the GRB originated from a tightly bound binary system of a neutron star and supergiant helium star that merged, producing a jet within a common gas envelope. The other study proposes that a minor body like an asteroid or comet was tidally disrupted after passing close to a neutron star, producing debris that formed a disk and caused multiple emission peaks.
While both models can explain aspects of the complex data from the unusual GRB, the article notes that at least one model must be incorrect as the definitive proof
The document analyzes ionospheric scintillation characteristics in the sub-Antarctic region based on GNSS data collected at Macquarie Island from 2011-2015. It investigates both the temporal and spatial characteristics of scintillation. Temporally, it finds that amplitude scintillation occurrence is closely related to solar activity, while phase scintillation is more influenced by geomagnetic activity. Spatially, phase scintillation consistently focuses on two regions, but the active region for amplitude scintillation changes yearly. The analysis provides insight into scintillation mechanisms in the sub-Antarctic region.
A mildly relativistic wide-angle outflow in the neutron-star merger event GW1...Sérgio Sacani
GW170817 was the first gravitational wave detection of a binary
neutron-star merger1
. It was accompanied by radiation across the
electromagnetic spectrum and localized2
to the galaxy NGC 4993
at a distance of 40 megaparsecs. It has been proposed that the
observed γ-ray, X-ray and radio emission is due to an ultrarelativistic
jet launched during the merger, directed away from
our line of sight3–6. The presence of such a jet is predicted from
models that posit neutron-star mergers as the central engines
that drive short hard γ-ray bursts7,8
. Here we report that the radio
light curve of GW170817 has no direct signature of an off-axis
jet afterglow. Although we cannot rule out the existence of a jet
pointing elsewhere, the observed γ-rays could not have originated
from such a jet. Instead, the radio data require a mildly relativistic
wide-angle outflow moving towards us. This outflow could be the
high-velocity tail of the neutron-rich material dynamically ejected
during the merger or a cocoon of material that breaks out when a
jet transfers its energy to the dynamical ejecta. The cocoon model
explains the radio light curve of GW170817 as well as the γ-rays
and X-rays (possibly also ultraviolet and optical emission)9–15, and
is therefore the model most consistent with the observational data.
Cocoons may be a ubiquitous phenomenon produced in neutronstar
mergers, giving rise to a heretofore unidentified population of
radio, ultraviolet, X-ray and γ-ray transients in the local Universe
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
The internal structure_of_asteroid_itokawa_as_revealed_by_detection_of_yorp_s...Sérgio Sacani
The study detected an acceleration in the rotation rate of asteroid (25143) Itokawa through long-term photometric monitoring between 2001-2013. By measuring rotational phase offsets between observed and modeled lightcurves, a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2 was measured, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year. Thermophysical analysis of the detailed shape model from the Hayabusa spacecraft found that the center-of-mass must be offset by about 21 m along the long axis to reconcile the observed and theoretical YORP strengths, suggesting Itokawa is composed of two separate bodies with densities of 1750 ± 110 kg m
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
An Earth-sized exoplanet with a Mercury-like compositionSérgio Sacani
Earth, Venus, Mars and some extrasolar terrestrial planets1
have a mass and radius that is consistent with a mass fraction
of about 30% metallic core and 70% silicate mantle2
. At the
inner frontier of the Solar System, Mercury has a completely
different composition, with a mass fraction of about 70%
metallic core and 30% silicate mantle3
. Several formation or
evolution scenarios are proposed to explain this metal-rich
composition, such as a giant impact4, mantle evaporation5
or the depletion of silicate at the inner edge of the protoplanetary
disk6. These scenarios are still strongly debated.
Here, we report the discovery of a multiple transiting planetary
system (K2-229) in which the inner planet has a radius
of 1.165 ± 0.066 Earth radii and a mass of 2.59 ± 0.43 Earth
masses. This Earth-sized planet thus has a core-mass fraction
that is compatible with that of Mercury, although it was
expected to be similar to that of Earth based on host-star
chemistry7
. This larger Mercury analogue either formed with
a very peculiar composition or has evolved, for example, by
losing part of its mantle. Further characterization of Mercurylike
exoplanets such as K2-229 b will help to put the detailed
in situ observations of Mercury (with MESSENGER and
BepiColombo8) into the global context of the formation and
evolution of solar and extrasolar terrestrial planets.
Toward a new_distance_to_the_active_galaxy_ngc4258Sérgio Sacani
This document reports on measurements of centripetal accelerations of maser spectral components in the active galaxy NGC 4258 using data from 51 epochs spanning 1994 to 2004. Accelerations of high-velocity maser emission indicate an origin within 13 degrees of the disk midline. Accelerations do not support a model of trailing shocks from spiral arms but find evidence of spiral structure with a wavelength of 0.75 mas. Accelerations of low-velocity emission are consistent with originating from a concave region where the thin disk is tangent to the line of sight.
The stelar mass_growth_of_brightest_cluster_galaxies_in_the_irac_shallow_clus...Sérgio Sacani
This document describes a study of the stellar mass growth of brightest cluster galaxies (BCGs) between z=1.5 and z=0.5 using data from the Spitzer IRAC Shallow Cluster Survey (ISCS). The researchers developed a method to select high-redshift clusters as progenitors of lower-redshift clusters to study the evolution of BCG stellar masses. They find that between z=1.5 and z=0.5, the BCGs grew in stellar mass by a factor of 2.3, matching predictions from a semi-analytic galaxy formation model. Below z=0.5, there are hints of differences between the observed BCG growth and the model predictions.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
More Related Content
Similar to The solar dynamo begins near the surface
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
A rock composition_for_earth_sized_exoplanetsSérgio Sacani
1) Researchers measured the mass of Kepler-78b, an Earth-sized exoplanet orbiting its host star every 8.5 hours, to be 1.69 ± 0.41 M⊕ using Doppler spectroscopy of the star's radial velocity variations.
2) Given the planet's radius of 1.20 ± 0.09 R⊕, its mean density of 5.3 ± 1.8 g/cm3 is similar to Earth's, suggesting a rocky composition of iron and rock.
3) Kepler-78b is the smallest exoplanet yet characterized with both an accurate mass and radius measurement, extending measurements of planetary composition into the size range of Earth and Venus.
1) PSR J033711715 is a millisecond pulsar discovered to be in a hierarchical triple system with two white dwarf companions, making it the first known millisecond pulsar triple system.
2) Precise timing observations using multiple radio telescopes determined the masses of the pulsar (1.4378 solar masses), inner white dwarf companion (0.19751 solar masses), and outer white dwarf companion (0.4101 solar masses) to high precision.
3) The unexpectedly coplanar and nearly circular orbits of the system indicate an exotic evolutionary history and provide an opportunity to test theories of general relativity by studying the interactions between the bodies.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
Is the atmosphere of the ultra-hot Jupiter WASP-121 b variable?Sérgio Sacani
We present a comprehensive analysis of the Hubble Space Telescope observations of the atmosphere
of WASP-121 b, a ultra-hot Jupiter. After reducing the transit, eclipse, and phase-curve observations
with a uniform methodology and addressing the biases from instrument systematics, sophisticated
atmospheric retrievals are used to extract robust constraints on the thermal structure, chemistry, and
cloud properties of the atmosphere. Our analysis shows that the observations are consistent with a
strong thermal inversion beginning at ∼104 Pa on the dayside, solar to subsolar metallicity Z (i.e.,
−0.77 < log(Z) < 0.05), and super-solar C/O ratio (i.e., 0.59 < C/O < 0.87). More importantly,
utilizing the high signal-to-noise ratio and repeated observations of the planet, we identify the following
unambiguous time-varying signals in the data: i) a shift of the putative hotspot offset between the
two phase-curves and ii) varying spectral signatures in the transits and eclipses. By simulating the
global dynamics of WASP-121 b atmosphere at high-resolution, we show that the identified signals are
consistent with quasi-periodic weather patterns, hence atmospheric variability, with signatures at the
level probed by the observations (∼5% to ∼10%) that change on a timescale of ∼5 planet days; in
the simulations, the weather patterns arise from the formation and movement of storms and fronts,
causing hot (as well as cold) patches of atmosphere to deform, separate, and mix in time.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Evidence for baryon acoustic oscillations from galaxy–ellipticity correlationsSérgio Sacani
The baryon acoustic oscillation feature in the clustering of galaxies
or quasars provides a ‘standard ruler’ for distance measurements in
cosmology. In this work, we report a 2–3σ signal of the baryon acoustic
oscillation dip feature in the galaxy density–ellipticity cross-correlation
functions using the spectroscopic sample of the Baryon Oscillation
Spectroscopic Survey CMASS, combined with the deep Dark Energy
Spectroscopic Instrument Legacy Imaging Surveys for precise galaxy shape
measurements. We measure the galaxy–ellipticity correlation functions and
model them using the linear alignment model. We constrain the distance
DV/rd to redshift 0.57 to a precision of 3–5%, depending on the details of
modelling. The galaxy–ellipticity measurement reduces the uncertainty
of distance measurement by ~10% on top of that derived from the galaxy–
galaxy correlation. More importantly, for future large and deep galaxy
surveys, the independent galaxy–ellipticity measurements can help sort out
the systematics in the baryon acoustic oscillation studies.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
The tumbling rotational state of 1I/‘OumuamuaSérgio Sacani
The discovery1
of 1I/2017 U1 (1I/‘Oumuamua) has provided
the first glimpse of a planetesimal born in another planetary
system. This interloper exhibits a variable colour within a
range that is broadly consistent with local small bodies, such
as the P- and D-type asteroids, Jupiter Trojans and dynamically
excited Kuiper belt objects2–7
. 1I/‘Oumuamua appears
unusually elongated in shape, with an axial ratio exceeding
5:1 (refs 1,4,5,8). Rotation period estimates are inconsistent
and varied, with reported values between 6.9 and 8.3 h
(refs 4–6,9). Here, we analyse all the available optical photometry
data reported to date. No single rotation period can explain
the exhibited brightness variations. Rather, 1I/‘Oumuamua
appears to be in an excited rotational state undergoing nonprincipal
axis rotation, or tumbling. A satisfactory solution
has apparent lightcurve frequencies of 0.135 and 0.126 h−1
and
implies a longest-to-shortest axis ratio of ≳5:1, although the
available data are insufficient to uniquely constrain the true
frequencies and shape. Assuming a body that responds to
non-principal axis rotation in a similar manner to Solar System
asteroids and comets, the timescale to damp 1I/‘Oumuamua’s
tumbling is at least one billion years. 1I/‘Oumuamua was
probably set tumbling within its parent planetary system and
will remain tumbling well after it has left ours.
This research news article discusses two studies that propose different models to explain an unusual gamma-ray burst (GRB) called the "Christmas burst" that occurred on Christmas Day in 2010.
One study suggests the GRB originated from a tightly bound binary system of a neutron star and supergiant helium star that merged, producing a jet within a common gas envelope. The other study proposes that a minor body like an asteroid or comet was tidally disrupted after passing close to a neutron star, producing debris that formed a disk and caused multiple emission peaks.
While both models can explain aspects of the complex data from the unusual GRB, the article notes that at least one model must be incorrect as the definitive proof
The document analyzes ionospheric scintillation characteristics in the sub-Antarctic region based on GNSS data collected at Macquarie Island from 2011-2015. It investigates both the temporal and spatial characteristics of scintillation. Temporally, it finds that amplitude scintillation occurrence is closely related to solar activity, while phase scintillation is more influenced by geomagnetic activity. Spatially, phase scintillation consistently focuses on two regions, but the active region for amplitude scintillation changes yearly. The analysis provides insight into scintillation mechanisms in the sub-Antarctic region.
A mildly relativistic wide-angle outflow in the neutron-star merger event GW1...Sérgio Sacani
GW170817 was the first gravitational wave detection of a binary
neutron-star merger1
. It was accompanied by radiation across the
electromagnetic spectrum and localized2
to the galaxy NGC 4993
at a distance of 40 megaparsecs. It has been proposed that the
observed γ-ray, X-ray and radio emission is due to an ultrarelativistic
jet launched during the merger, directed away from
our line of sight3–6. The presence of such a jet is predicted from
models that posit neutron-star mergers as the central engines
that drive short hard γ-ray bursts7,8
. Here we report that the radio
light curve of GW170817 has no direct signature of an off-axis
jet afterglow. Although we cannot rule out the existence of a jet
pointing elsewhere, the observed γ-rays could not have originated
from such a jet. Instead, the radio data require a mildly relativistic
wide-angle outflow moving towards us. This outflow could be the
high-velocity tail of the neutron-rich material dynamically ejected
during the merger or a cocoon of material that breaks out when a
jet transfers its energy to the dynamical ejecta. The cocoon model
explains the radio light curve of GW170817 as well as the γ-rays
and X-rays (possibly also ultraviolet and optical emission)9–15, and
is therefore the model most consistent with the observational data.
Cocoons may be a ubiquitous phenomenon produced in neutronstar
mergers, giving rise to a heretofore unidentified population of
radio, ultraviolet, X-ray and γ-ray transients in the local Universe
The Internal Structure of Asteroid (25143) Itokawa as Revealed by Detection o...WellingtonRodrigues2014
- The authors detected an acceleration in the rotation rate of asteroid (25143) Itokawa through photometric observations spanning 2001 to 2013.
- By measuring rotational phase offsets between observed and modeled lightcurves, they found a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year.
- Thermophysical modeling of the detailed shape model from the Hayabusa spacecraft could not reconcile the observed YORP strength unless the asteroid's center of mass is shifted by about 21 m along its long axis. This suggests Itokawa has two components with different densities that merged, either from a
The internal structure_of_asteroid_itokawa_as_revealed_by_detection_of_yorp_s...Sérgio Sacani
The study detected an acceleration in the rotation rate of asteroid (25143) Itokawa through long-term photometric monitoring between 2001-2013. By measuring rotational phase offsets between observed and modeled lightcurves, a YORP acceleration of 3.54 ± 0.38 × 10−8 rad day−2 was measured, equivalent to a decrease in the asteroid's rotation period of about 45 ms per year. Thermophysical analysis of the detailed shape model from the Hayabusa spacecraft found that the center-of-mass must be offset by about 21 m along the long axis to reconcile the observed and theoretical YORP strengths, suggesting Itokawa is composed of two separate bodies with densities of 1750 ± 110 kg m
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
An Earth-sized exoplanet with a Mercury-like compositionSérgio Sacani
Earth, Venus, Mars and some extrasolar terrestrial planets1
have a mass and radius that is consistent with a mass fraction
of about 30% metallic core and 70% silicate mantle2
. At the
inner frontier of the Solar System, Mercury has a completely
different composition, with a mass fraction of about 70%
metallic core and 30% silicate mantle3
. Several formation or
evolution scenarios are proposed to explain this metal-rich
composition, such as a giant impact4, mantle evaporation5
or the depletion of silicate at the inner edge of the protoplanetary
disk6. These scenarios are still strongly debated.
Here, we report the discovery of a multiple transiting planetary
system (K2-229) in which the inner planet has a radius
of 1.165 ± 0.066 Earth radii and a mass of 2.59 ± 0.43 Earth
masses. This Earth-sized planet thus has a core-mass fraction
that is compatible with that of Mercury, although it was
expected to be similar to that of Earth based on host-star
chemistry7
. This larger Mercury analogue either formed with
a very peculiar composition or has evolved, for example, by
losing part of its mantle. Further characterization of Mercurylike
exoplanets such as K2-229 b will help to put the detailed
in situ observations of Mercury (with MESSENGER and
BepiColombo8) into the global context of the formation and
evolution of solar and extrasolar terrestrial planets.
Toward a new_distance_to_the_active_galaxy_ngc4258Sérgio Sacani
This document reports on measurements of centripetal accelerations of maser spectral components in the active galaxy NGC 4258 using data from 51 epochs spanning 1994 to 2004. Accelerations of high-velocity maser emission indicate an origin within 13 degrees of the disk midline. Accelerations do not support a model of trailing shocks from spiral arms but find evidence of spiral structure with a wavelength of 0.75 mas. Accelerations of low-velocity emission are consistent with originating from a concave region where the thin disk is tangent to the line of sight.
The stelar mass_growth_of_brightest_cluster_galaxies_in_the_irac_shallow_clus...Sérgio Sacani
This document describes a study of the stellar mass growth of brightest cluster galaxies (BCGs) between z=1.5 and z=0.5 using data from the Spitzer IRAC Shallow Cluster Survey (ISCS). The researchers developed a method to select high-redshift clusters as progenitors of lower-redshift clusters to study the evolution of BCG stellar masses. They find that between z=1.5 and z=0.5, the BCGs grew in stellar mass by a factor of 2.3, matching predictions from a semi-analytic galaxy formation model. Below z=0.5, there are hints of differences between the observed BCG growth and the model predictions.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
Similar to The solar dynamo begins near the surface (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
Or: Beyond linear.
Abstract: Equivariant neural networks are neural networks that incorporate symmetries. The nonlinear activation functions in these networks result in interesting nonlinear equivariant maps between simple representations, and motivate the key player of this talk: piecewise linear representation theory.
Disclaimer: No one is perfect, so please mind that there might be mistakes and typos.
dtubbenhauer@gmail.com
Corrected slides: dtubbenhauer.com/talks.html
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
ESPP presentation to EU Waste Water Network, 4th June 2024 “EU policies driving nutrient removal and recycling
and the revised UWWTD (Urban Waste Water Treatment Directive)”
Unlocking the mysteries of reproduction: Exploring fecundity and gonadosomati...AbdullaAlAsif1
The pygmy halfbeak Dermogenys colletei, is known for its viviparous nature, this presents an intriguing case of relatively low fecundity, raising questions about potential compensatory reproductive strategies employed by this species. Our study delves into the examination of fecundity and the Gonadosomatic Index (GSI) in the Pygmy Halfbeak, D. colletei (Meisner, 2001), an intriguing viviparous fish indigenous to Sarawak, Borneo. We hypothesize that the Pygmy halfbeak, D. colletei, may exhibit unique reproductive adaptations to offset its low fecundity, thus enhancing its survival and fitness. To address this, we conducted a comprehensive study utilizing 28 mature female specimens of D. colletei, carefully measuring fecundity and GSI to shed light on the reproductive adaptations of this species. Our findings reveal that D. colletei indeed exhibits low fecundity, with a mean of 16.76 ± 2.01, and a mean GSI of 12.83 ± 1.27, providing crucial insights into the reproductive mechanisms at play in this species. These results underscore the existence of unique reproductive strategies in D. colletei, enabling its adaptation and persistence in Borneo's diverse aquatic ecosystems, and call for further ecological research to elucidate these mechanisms. This study lends to a better understanding of viviparous fish in Borneo and contributes to the broader field of aquatic ecology, enhancing our knowledge of species adaptations to unique ecological challenges.
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
1. Nature | Vol 629 | 23 May 2024 | 769
Article
Thesolardynamobeginsnearthesurface
Geoffrey M. Vasil1✉, Daniel Lecoanet2,3
, Kyle Augustson2,3
, Keaton J. Burns4,5
, Jeffrey S. Oishi6
,
Benjamin P. Brown7
, Nicholas Brummell8
& Keith Julien9,10
ThemagneticdynamocycleoftheSunfeaturesadistinctpattern:apropagating
regionofsunspotemergenceappearsaround30°latitudeandvanishesnearthe
equatorevery11 years(ref. 1).Moreover,longitudinalflowscalledtorsionaloscillations
closelyshadowsunspotmigration,undoubtedlysharingacommoncause2
.Contrary
totheoriessuggestingdeeporiginsofthesephenomena,helioseismologypinpoints
low-latitudetorsionaloscillationstotheouter5–10%oftheSun,thenear-surface
shearlayer3,4
.Withinthiszone,inwardlyincreasingdifferentialrotationcoupledwith
apoloidalmagneticfieldstronglyimplicatesthemagneto-rotationalinstability5,6
,
prominentinaccretion-disktheoryandobservedinlaboratoryexperiments7
.
Together,thesetwofactspromptthegeneralquestion:whetherthesolardynamois
possiblyanear-surfaceinstability.Herewereportstrongaffirmativeevidenceinstark
contrasttotraditionalmodels8
focusingonthedeepertachocline.Simpleanalytic
estimatesshowthatthenear-surfacemagneto-rotationalinstabilitybetterexplains
thespatiotemporalscalesofthetorsionaloscillationsandinferredsubsurface
magneticfieldamplitudes9
.State-of-the-artnumericalsimulationscorroboratethese
estimatesandreproducehemisphericalmagneticcurrenthelicitylaws10
.Thedynamo
resultingfromawell-understoodnear-surfacephenomenonimprovesprospects
foraccuratepredictionsoffullmagneticcyclesandspaceweather,affectingthe
electromagneticinfrastructureofEarth.
Keyobservationsthatanymodelmusttakeintoaccountinclude(1)the
solarbutterflydiagram,adecadalmigrationpatternofsunspotemer-
gence1,4
withstronglatitudedependence;(2)thetorsionaloscillations
constituting local rotation variations corresponding with magnetic
activity2–4
;(3)thepoloidalfield,anapproximately1 Gphotosphericfield
witha1/4-cyclephaselagrelativetosunspots11
,andapproximately100 G
subsurface amplitudes9
; (4) the hemispherical helicity sign rule com-
prisinganempiricallyobservednegativecurrenthelicityinthenorthern
hemisphere and positive current helicity in the south10
; (5) the tacho-
cline at the base of the convection zone, the traditionally proposed
seat of the solar dynamo; and (6) the near-surface-shear layer (NSSL)
withintheouter5–10%oftheSuncontainingstronginwardlyincreasing
angular velocity fostering the magneto-rotational instability (MRI).
Despiteprogress,prevailingtheorieshavedistinctlimitations.Inter-
facedynamos(proposedwithinthetachocline8
)preferentiallygener-
ate high-latitude fields12
and produce severe shear disruptions13
that
are not observed14
. Mean-field dynamos offer qualitative insights but
suffer from the absence of first principles15
and are contradicted by
observed meridional circulations16
. Global convection-zone models
oftenmisalignwithimportantsolarobservations,requireconditions
divergingfromsolarreality17–19
andfailtoprovideatheoreticaldynami-
cal understanding.
Borrowing from well-established ideas in accretion-disk physics5,6
,
weproposeanalternativehypothesisthatproducesclearpredictions
and quantitatively matches key observations.
ForelectricallyconductingplasmasuchastheSun,thelocalaxisym-
metric linear instability criterion for the MRI is5,6
ΩS ω
2 > , (1)
A
2
where the local Alfvén frequency and shear are
ω
B k
ρ
S r
Ω
r
=
4π
and = −
d
d
. (2)
r
A
0
0
The system control parameters are the background poloidal mag-
netic field strength (B0 in cgs units), the atmospheric density (ρ0),
the smallest non-trivial radial wavenumber that will fit in the domain
(kr ≈ π/Hr, where Hr is a relevant layer depth or density-scale height),
bulkrotationrate(Ω)andthedifferentialrotation,orshear(S > 0inthe
NSSL).Anadiabaticdensitystratificationholdstoagoodapproxima-
tionwithinthesolarconvectionzone,eliminatingbuoyancymodifica-
tions to the stability condition in equation (1).
The MRI is essential for generating turbulent angular momentum
transport in magnetized astrophysical disks6
. Previous work20
pos-
tulated the NSSL as the possible seat of the global dynamo without
invokingtheMRI.Akinematicdynamostudy21
dismissedtherelevance
ofNSSLbutdidnotallowforfullmagnetohydrodynamic(MHD)insta-
bilities(suchastheMRI).Modernbreakthroughsinourunderstanding
oflarge-scaleMRIphysics22,23
havenotbeenappliedinasolarcontext,
https://doi.org/10.1038/s41586-024-07315-1
Received: 19 August 2023
Accepted: 14 March 2024
Published online: 22 May 2024
Open access
Check for updates
1
School of Mathematics and the Maxwell Institute for Mathematical Sciences, University of Edinburgh, Edinburgh, UK. 2
Department of Engineering Sciences and Applied Mathematics,
Northwestern University, Evanston, IL, USA. 3
CIERA, Northwestern University, Evanston, IL, USA. 4
Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA, USA.
5
Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA. 6
Department of Physics and Astronomy, Bates College, Lewiston, ME, USA. 7
Department of Astrophysical and
Planetary Sciences, University of Colorado Boulder, Boulder, CO, USA. 8
Department of Applied Mathematics, Jack Baskin School of Engineering, University of California Santa Cruz, Santa Cruz,
CA, USA. 9
Department of Applied Mathematics, University of Colorado Boulder, Boulder, CO, USA. 10
Deceased: Keith Julien. ✉e-mail: gvasil@ed.ac.uk
2. 770 | Nature | Vol 629 | 23 May 2024
Article
andlocalMRIstudiesoftheSun24
haveconsideredonlysmallscales.To
ourknowledge,noworkhasyetconsideredlarge-scaleMRIdynamics
relevant to the observed features of the global dynamo. We therefore
describe here a potential MRI-driven solar dynamo cycle.
The start of the solar cycle is the period surrounding the sunspot
minimum when there is no significant toroidal field above the equa-
tor and a maximal poloidal field below the photosphere. This con-
figuration is unstable to the axisymmetric MRI, which generates a
dynamically active toroidal field in the outer convection zone. The
observed torsional oscillations are the longitudinal flow perturba-
tionsarisingfromtheMRI.Therelativeenergeticsareconsistentwith
nonlinear dynamo estimates (Methods). As the cycle progresses, the
toroidalfieldcanundergoseveralpossibleMHDinstabilitiescontrib-
uting to poloidal-field regeneration, for example, the helical MRI,
non-axis-symmetric MRI, the clamshell instability and several more,
including a surface Babcock–Leighton process. We propose that the
axisymmetric subsurface field and torsional oscillations constitute
a nonlinear MRI travelling wave. The instability saturates by radial
transportof(globallyconserved)meanmagneticflux(B0)andangular
momentum (Ω, S), which neutralize the instability criterion in equa-
tion (1) (Methods).
Empiricaltimescalesofthetorsionaloscillationsimplyanapproxi-
mate growth rate, γ, for the MRI and, therefore, a relevant poloidal
fieldstrength.Toagoodapproximation,S ≈ Ω ≈ 2π/monthintheNSSL
(Fig.1a–c).Theearly-phasetorsionaloscillationschangeonatimescale
of 2–12 months, implying a growth rate of γ/Ω ≈ 0.01–0.1 (Methods).
A modest growth rate and the regularity of the solar cycle over long
intervalstogethersuggestthattheglobaldynamicsoperateinamildly
nonlinear regime. Altogether, we predict roughly ωA ≈ S ≈ Ω.
The torsional oscillation pattern shows an early-phase mode-like
structurewithanapproximately4:1horizontalaspectratiooccupying
adepthofroughlyr/R⊙ ≈ 5%,or ⊙
k R
≈ 70
r
−1
(Fig.1d).Usingequation(2),
the approximate background Alfvén speed vA ≈ 200–2,000 cm s−1
≈
0.1–1.0 R⊙/year.
Alfvén-speed estimates required for MRI dynamics are consistent
withobservedinternalmagneticfieldstrengths.Measurementssuggest
100–200 Ginternalpoloidalfield9
,agreeingwiththeaboveestimates
using NSSL densities ρ0 ≈ 3 × 10−2
g cm−3
to 3 × 10−4
g cm−3
. The same
min+1yr – min min+2yr – min min+3yr – min min+4yr – min
–1.0
–0.5
0
nHz
0.5
1.0
0 0.2 0.4 0.6 0.8 1.0
r/R(
0
0.2
0.4
0.6
0.8
1.0
Ω
300
350
400
450
nHz
0 0.2 0.4 0.6 0.8 1.0
0
0.2
0.4
0.6
0.8
1.0
sin(T)w
T
Ω
−100
−50
0
50
100
nHz
0 0.2 0.4 0.6 0.8 1.0
0
0.2
0.4
0.6
0.8
1.0
−500
0
500
nHz
a b c
d
r/R( r/R(
r
sin(T)w
r
Ω
Fig.1|Measuredinternalsolarrotationprofiles.a,Heliosesimicdifferential
rotationprofile, Ω(θ, r) usingpublicly available datafromref. 29.b,c,The
respectivelatitudinaland radialsheargradients r θ Ω θ r
∇
∇
sin( ) ( , )computedbya
non-uniformfourth-ordercentredfinite-differencescheme.Thelatitudinal
meanoftachoclineshearisabout200 nHzandpeakamplitudesarebelow
about350 nHz.Conversely,thenear-surfaceshearaveragesabout400–600 nHz
(withrapidvariationindepth)andpeakvaluesaveragearound1,200 nHz.
d,Helioseismicmeasurementsofsolartorsionaloscillations.Theredshows
positiveresidualrotationratesandblueshowsnegativeresidualrotationrates
afterremovingthe1996annualmeanofΩ(r, θ).Eachsliceshowstherotational
perturbations1,2,3and4yearsaftertheapproximatesolarminimum.The
notation‘min+1yr–min’meanstakingtheprofileat1yearpastsolarminimum
andsubtractingtheprofileatsolarminimum.Thecolourtablesaturatesat
±1 nHz,correspondingtoabout400 cm s−1
surfaceflowamplitude.Further
contourlinesshow1 nHzincrementswithinthesaturatedregions.Diagramind
reproducedwithpermissionfromfigure2inref.3,AAAS.
3. Nature | Vol 629 | 23 May 2024 | 771
studies found roughly similar (300–1,000 G) internal toroidal field
strengthconfinedwithintheNSSL.Givensolar-likeinputparameters,a
detailedcalculationshowsthattheMRIshouldoperatewithlatitudinal
field strengths up to about 1,000 G (Methods).
Background shear modification dominates the MRI saturation
mechanism (Methods), roughly
Ω
H
R
ΩS ω S ω
Ω S Ω S Ω ω
′ ≈
(2 − )( + )
2 ( + 2 )( + (2 ) + 2 )
, (3)
r
2
2
2
A
2 2
A
2 2
2 2
A
2
∣ ∣
⊙
whereΩ′representsthedynamicchangesindifferentialrotation.For
S ≈ Ω ≈ ωA,|Ω′| ≈ 7 nHz,roughlyconsistentwiththeobservedtorsional
oscillation amplitude (Fig. 1d).
WecomputeasuiteofgrowingglobalperturbationsusingDedalus25
to model the initial phase of the solar cycle with quasi-realistic solar
inputparameters(Methods).Figure2showsrepresentativesolutions.
Wefindtwodistinctcases:(1)afastbranchwithdirectgrowthrates,
γ, comparable to a priori estimates and (2) a slow branch with longer
butrelevantgrowthtimesandoscillationperiods.Theeigenmodesare
confinedtotheNSSL,reachingfromthesurfacetor/R⊙ ≈ 0.90–0.95,at
which point the background shear becomes MRI stable.
For case 1, γ/Ω0 ≈ 6 × 10−2
(given Ω0 = 466 nHz) with corresponding
e-folding time, te ≈ 60 days and no discernible oscillation frequency.
Thepatterncomprisesroughlyonewaveperiodbetweentheequator
and about 20° latitude, similar to the rotation perturbations seen in
the torsional oscillations.
Forcase2,γ/Ω0 ≈ 6 × 10−3
withte ≈ 600 daysandoscillationfrequency
ω/Ω0 ≈ 7 × 10−3
, corresponding to a period P ≈ 5 years. The pattern
comprises roughly one wave period between the equator and about
20°–30° latitude.
Apart from cases 1 and 2, we find 34 additional purely growing
fast-branch modes, two additional oscillatory modes and one inter-
mediate exceptional mode (Extended Data Figs. 1–3).
Using the full numerical MHD eigenstates, we compute a system-
atic estimate for the saturation amplitude using quasi-linear theory
(Methods):|Ω′|≈6nHzforcase1and|Ω′|≈3nHzforcase2;bothcom-
parabletotheobservedtorsionaloscillationamplitudeandthesimple
analyticalestimatesfromequation(3).Thetruesaturatedstatewould
compriseaninteractingsuperpositionofthefullspectrumofmodes.
Notably,theslow-branchcurrenthelicity, b b
H ∇
∇
∝ ⋅ × ,followsthe
hemisphericalsignrule10
,with < 0
H inthenorthand > 0
H inthesouth.
Theslow-branchmodesseemtoberotationallyconstrained,consist-
ent with their low Rossby number26
, providing a pathway for under-
standing the helicity sign rule.
Further helioseismic data analyses could test our predictions. The
MRI would not operate if the poloidal field is too strong, nor would
it explain the torsional oscillations if it is too weak. We predict cor-
relations between the flow perturbations and magnetic fields, which
time-resolvedmeasurementscouldtest,constrainingjointhelioseismic
inversions of flows and magnetic fields.
AnMRI-drivendynamomayalsoexplaintheformationandcessation
of occasional grand minima27
(for example, Maunder). As an essen-
tiallynonlineardynamo,theMRIisnotatraditionalkinematicdynamo
startingfromaninfinitesimalseedfieldoneachnewcycle(Methods).
Rather,amoderatepoloidalfieldexistsatthesolarminimum,andthe
MRI processes it into a toroidal configuration. If the self-sustaining
poloidal-to-toroidal regeneration sometimes happens imperfectly,
then subsequent solar cycles could partially fizzle, leading to weak
subsurface fields and few sunspots. Eventually, noise could push the
systembackontoitsnormalcyclicbehaviour,asintheElNinoSouthern
Oscillation28
.
Finally, our simulations intentionally contain reduced physics to
isolatetheMRIasanimportantagentinthedynamoprocess,filtering
outlarge-scalebarocliniceffects,small-scaleconvectionandnonlinear
dynamo feedback. Modelling strong turbulent processes is arduous:
turbulence can simultaneously act as dissipation, drive large-scale
flowssuchastheNSSL,producemeanelectromotiveforcesandexcite
collectiveinstabilities.Althoughsufficientlystrongturbulentdissipa-
tioncouldeventuallyerasealllarge-scaledynamics,themerepresence
of the solar torsional oscillations implies much can persist within the
roiling background.
Onlinecontent
Anymethods,additionalreferences,NaturePortfolioreportingsumma-
ries,sourcedata,extendeddata,supplementaryinformation,acknowl-
edgements, peer review information; details of author contributions
andcompetinginterests;andstatementsofdataandcodeavailability
are available at https://doi.org/10.1038/s41586-024-07315-1.
1. Maunder, E. W. The Sun and sunspots, 1820–1920. (plates 13, 14, 15, 16.). Mon. Not. R.
Astron. Soc. 82, 534–543 (1922).
2. Snodgrass, H. B. & Howard, R. Torsional oscillations of the Sun. Science 228, 945–952 (1985).
3. Vorontsov, S. V., Christensen-Dalsgaard, J., Schou, J., Strakhov, V. N. & Thompson, M. J.
Helioseismic measurement of solar torsional oscillations. Science 296, 101–103 (2002).
4. Hathaway, D. H., Upton, L. A. & Mahajan, S. S. Variations in differential rotation and
meridional flow within the Sun’s surface shear layer 1996–2022. Front. Astron. Space Sci.
9, 1007290 (2022).
Ω
–1
1
1
1
–2.9
9
bI
–152
152
2
2
aI
–1.2
1.2
2
2
–2.2
2.2
–0.8
0.8
te = 60 days P = None
P = 1,835 days
te = 601 days
a
b
′
2.9
nHz
cm
s
–1
R
(
G
G
R
(
–1
1
nHz
–0.8
0.8
cm
s
–1
R
(
–197
197
G
–1.0
1.0
G
R
(
Ω bI aI
′
Fig.2|Twomeridional(r,θ)MRIeigenmodeprofiles.Longitudinalangular
velocity perturbation, Ω r θ u r θ r θ
′( , ) = ( , )/( sin( ))
ϕ ; momentum-density
streamfunction (ϕ-directed component; Methods), ψ(r, θ); longitudinal
magneticfield,bϕ(r, θ); magneticscalarpotential,aϕ(r, θ);andcurrenthelicity
correlation,H r θ
( , ).Thetimescaleste andPrepresenttheinstabilitye-folding
timeandoscillationperiod,respectively.a,Case1:atypicaldirectlygrowing
fast-branchmodewithnooscillationandgrowthratesγ ≈ 0.06Ω0.b,Case2:
atypicallarge-scaleslow-branchmodewitharoughly5-yearperiod.Ineach
case,wefixtheoverallamplitudeto1 nHzfortherotationalperturbations,
withallotherquantitiestakingtheircorrespondingrelativevalues.
5. Methods
Numericalcalculations
We solve for the eigenstates of the linearized anelastic MHD equa-
tions30,31
in spherical-polar coordinates (r, θ, ϕ) = (radius, colati-
tude, longitude). Using R⊙ = 6.96 × 1010
cm for the solar radius, we
simulate radii between r0 ≤ r ≤ r1 where r0/R⊙ = 0.89 and r1/R⊙ = 0.99.
We place the top of the domain at 99% because several complicated
processes quickly increase in importance between this region and
the photosphere (for example, partial ionisation, radiative trans-
port and much stronger convection effects). We use the anelastic
MHD equations in an adiabatic background to capture the effects
of density stratification on the background Alfvén velocities (den-
sity varies by roughly a factor of 100 across the NSSL, causing about
a factor of 10 change in Alfvén speed) and asymmetries in velocity
structures introduced by the density stratification by ∇ ⋅ (ρu). A key
aspect of the anelastic approximation is that all entropy perturba-
tions must be small, which is reasonable in the NSSL below 0.99R⊙.
We do not use the fully compressible equations, as these linear insta-
bility modes do not have acoustic components. Future MRI studies
incorporatingbuoyancyeffects(forexample,thedeepMRIbranches
at high latitudes) should use a fully compressible (but low Mach
number) model32
.
Input background parameters. We include density stratification
usingalow-orderpolynomialapproximationtotheModel-Sprofile33
.
Inunitsofg cm−3
,withh = (r − r0)/(r1 − r0),
ρ α α h α h α h α h
= − + − + , (4)
0 0 1 2
2
3
3
4
4
α = 0.031256, (5)
0
α = 0.053193, (6)
1
α = 0.033703, (7)
2
α = 0.023766, (8)
3
α = 0.012326, (9)
4
whichfitstheModel-Sdatatobetterthan1%withinthecomputational
domain.Thedensityath= 1isρ0 = 0.000326comparedwith0.031256
at h = 0.
Thedensityprofileisclosetoanadiabaticpolytropewithr−2
gravity
and 5/3 adiabatic index. An adiabatic background implies that buoy-
ancy perturbations diffuse independently of the MHD and decouple
from the system.
Weusealow-degreepolynomialfittotheobservedNSSLdifferential
rotation profile. For μ = cos(θ),
u e
Ω r θ r θ
= ( , ) sin( ) , (10)
ϕ
0
Ω r θ Ω R h μ
( , ) = ( ) Θ( ), (11)
0
where Ω0 = 466 nHz ≈ 2.92 × 10−6
s−1
and
R h h h h
( ) = 1 + 0.02 − 0.01 − 0.03 , (12)
2 3
μ μ μ
Θ( ) = 1 − 0.145 − 0.148 . (13)
2 4
We use the angular fit from ref. 34. The radial approximation results
from fitting the equatorial profile from ref. 29 shown in Fig. 1a.
Below 60° latitude, the low-degree approximation agrees with the
full empirical profile to within 1.25%. The high-latitude differen-
tial rotation profile is less constrained because of observational
uncertainties.
We define the background magnetic field in terms of a vector
potential,
∇
∇
= × , (14)
0 0
B A
B r
r θ
=
( )
2
sin( ) , (15)
ϕ
0
A e
where
B r B r r r r
( ) = (( / ) − ( / ) ), (16)
0 1
−3
1
2
andB0 = 90 G.Ther−3
termrepresentsaglobaldipole.Ther2
termrep-
resentsafieldwithasimilarstructurebutcontainingelectriccurrent,
J
B
e
B
r
r θ
∇
∇
=
×
4π
=
5
4π
sin( ) . (17)
ϕ
0
0 0
1
2
The background field is in MHD force balance,
∇
∇
× = ( ⋅ ). (18)
0 0 0 0
J B A J
TheMHDforcebalancegeneratesmagneticpressure,whichinevita-
bly produces entropy, s′, and enthalpy, h′, perturbations using
ρ
T s h
∇
∇
∇
∇ ∇
∇
( ⋅ )
+ ′= ′, (19)
0 0
0
0
A J
where
A J A J
s
Γ T ρ
h
Γ
Γ ρ
′=
1
− 1
⋅
, ′ =
− 1
⋅
, (20)
3
0 0
0 0
3
3
0 0
0
and Γ3 is the third adiabatic index. However, the MRI is a weak-field
instability, implying magnetic buoyancy and baroclinicity effects are
subdominant. For the work presented here, we neglect the contribu-
tions of magnetism to entropy (magnetic buoyancy) and consider
adiabatic motions. We expect this to be valid for MRI in the NSSL, but
studies of MRI in the deep convection zone at high latitudes would
need to incorporate these neglected effects.
We choose our particular magnetic field configuration rather than
a pure dipole because the radial component r θ
⋅ = ( )cos( )
r 0 B
e B van-
ishes at r = r1. The poloidal field strength in the photosphere is about
1 G, but measurements suggest sub-surface field strengths of about
50–150 G (ref. 9). The near-surface field should exhibit a strong hori-
zontal(asopposedtoradial)character.Magneticpumping35
bysurface
granulation within the outer 1% of the solar envelope could account
forfilteringtheoutwardradialfield,withsunspotcoresbeingpromi-
nent exceptions.
Wealsotestpuredipolesandfieldswithanapproximately5%dipole
contribution, yielding similar results. Furthermore, we test that the
poloidal field is stable to current-driven instabilities. Our chosen
confined field also has the advantage that eθ ⋅ B0 is constant to within
8% over r0 < r < r1. However, a pure dipole varies by about 37% across
the domain. The RMS field amplitude is ∣B∣RMS ≈ 2B0 = 180 G, about
25% larger than the maximum-reported inferred dipole equivalent9
.
However,projectingourfieldontoadipoletemplategivesanapproxi-
mately 70 G equivalent at the r = r1 equator. Overall, the sub-surface
field is the least constrained input to our calculations, the details of
which change over several cycles.
6. Article
Model equations.Respectively,thelinearizedanelasticmomentum,
mass-continuityandmagneticinductionequationsare
ρ ϖ ν ρ
∇
∇ ∇
∇
(∂ + × + × + ) = ⋅ ( ) + × + × , (21)
t
0 0 0 0 0 0
σ
u ω u ω u j B J b
ρ
∇
∇ ⋅ ( ) = 0, (22)
0
u
η ∇
∇
∂ − ∇ = × ( × + × ), (23)
t
2
0 0
b b u b u B
where the traceless strain rate
∇
∇ ∇
∇ ∇
∇
= + ( ) −
2
3
⋅ . (24)
σ u u u I
⊤
Tofindeigenstates,∂t → γ + iω,whereγisthereal-valuedgrowthrate,
andωisareal-valuedoscillationfrequency.Theinductionequation(23)
automatically produces MRI solutions satisfying ∇ ⋅ b = 0.
Giventhevelocityperturbation,u,thevorticityω = ∇ × u.Giventhe
magneticfield(Gaussincgsunits),thecurrentdensityperturbations
j = ∇ × b/4π.Atlinearorder,theBernoullifunctionϖ h
= ⋅ + ′
0
u u ,where
h′ represents enthalpy perturbations26
.
Thevelocityperturbationsareimpenetrable(ur = 0)andstress-free
(σrθ = σrϕ = 0)atbothboundaries.Forthemagneticfield,weenforceper-
fectconductingconditionsattheinnerboundary(br = ∂rbθ = ∂rbϕ = 0).At
theouterboundary,wetestthreedifferentchoicesincommonusage,
asdifferentmagneticboundaryconditionshavedifferentimplications
for magnetic helicity fluxes through the domain, and these can affect
global dynamo outcomes36
. Two choices with zero helicity flux are
perfectlyconductingandvacuumconditions,andwefindonlymodest
differences in the results. We also test a vertical field or open bound-
ary(thatis,∂rbr = bθ = bϕ = 0),which,althoughnon-physical,explicitly
allowsahelicityflux.Theseopensystemsalsohadessentiallythesame
results as the other two for growth rates and properties of eigenfunc-
tions.Weconductmostofourexperimentsusingperfectlyconducting
boundary conditions, which we prefer on the same physical grounds
as the background field.
We set constant and kinematic viscous and magnetic diffusivity
parametersν = η = 10−6
inunitswhereΩ0 = R⊙ = 1.ThemagneticPrandtl
numberν/η = Pm = 1assumesequaltransportofvectorsbytheturbu-
lentdiffusivities.AmoredetailedanalysisoftheshearReynoldsnum-
bers yields U L ν
Re = Rm = / ≈ 1,500
0 0 , where U0 ≈ 5,000 cm s−1
is the
maximum shear velocity jump across the NSSL and L0 ≈ 0.06R⊙ is the
distancebetweenminimumandmaximumshearvelocity(seesection
‘NSSL energetics and turbulence parameterization’ below).
We compute the following scalar-potential decompositions a
posteriori,
u e e
u
ρ
ρ ψ
∇
∇
= +
1
× ( ), (25)
ϕ ϕ ϕ
0
0
b a
∇
∇
= + × ( ), (26)
ϕ ϕ ϕ ϕ
b e e
whereboththemagneticscalarpotential,aϕ,andthestreamfunction,
ψ, vanish at both boundaries.
We, furthermore, compute the current helicity correlation relative
to global RMS values,
=
⋅
. (27)
RMS RMS
b j
b j
H
Thereisnoinitialhelicityinthebackgroundpoloidalmagneticfield,
A r θ
∇
∇ ∇
∇
= × ( ( , ) ) ⋅ ( × ) = 0.
ϕ
0 0 0 0
⇒
B e B B
Linear dynamical perturbations, b(r, θ), will locally align with the
background field and current. However, because the eigenmodes
arewave-like,thesecontributionsvanishexactlywhenaveragedover
hemispheres.
∇
∇ ∇
∇
⟨ ⋅ ( × )⟩ = ⟨ ⋅ ( × )⟩ = 0.
0 0
b B B b
The only possible hemispheric contributions arise when considering
quadratic mode interactions,
∇
∇
⟨ ⋅ ( × )⟩ ≠ 0.
b b
This order is the first for which we could expect a non-trivial signal.
Finally,wealsosolvethesystemusingseveraldifferentmathemati-
callyequivalentequationformulations(forexample,usingamagnetic
vectorpotentialb = ∇ × a,ordividingthemomentumequationsbyρ0).
Inallcases,wefindexcellentagreementintheconvergedsolutions.We
preferthisformulationbecauseofsatisfactorynumericalconditioning
as parameters become more extreme.
Computational considerations.TheDedaluscode25
usesgeneralten-
sorcalculusinspherical-polarcoordinatesusingspin-weightedspheri-
calharmonicsin(θ, ϕ)(refs. 37,38).Forthefiniteradialshell,thecode
usesaweightedgeneralizedChebyshevserieswithsparserepresenta-
tions for differentiation, radial geometric factors and non-constant
coefficients(forexample,ρ0(r)).Asthebackgroundmagneticfieldand
thedifferentialrotationareaxisymmetricandtheycontainonlyafew
low-orderseparabletermsinlatitudeandradius,thesetwo-dimensional
non-constant coefficients have a low-order representation in a joint
expansionofspin-vectorharmonicsandChebyshevpolynomials.The
resultisatwo-dimensionalgeneralizednon-Hermitianeigenvalueprob-
lem Ax = λBx, where x represents the full system spectral-space state
vector.Thematrices,AandB,arespectral-coefficientrepresentations
of the relevant linear differential and multiplication operators. Cases
1 and 2 use 384 latitudinal and 64 radial modes (equivalently spatial
points).ThematricesAandBremainsparse,withrespectivefillfactors
ofabout8 × 10−4
and4 × 10−5
.
The eigenvalues and eigenmodes presented here are converged to
better than 1% relative absolute error (comparing 256 and 384 latitu-
dinal modes). We also use two simple heuristics for rejecting poorly
convergedsolutions.First,becauseλ0 iscomplexvalued,theresulting
iteratedsolutionsdonotautomaticallyrespectHermitian-conjugate
symmetry,whichweoftenfindviolatedforspurioussolutions.Second,
the overall physical system is reflection symmetric about the equa-
tor, implying the solutions fall into symmetric and anti-symmetric
classes. Preserving the desired parity is a useful diagnostic tool for
rejecting solutions with mixtures of the two parities, which we check
individuallyforeachfieldquantity.Thepreciseparametersanddetailed
implementation scripts are available at GitHub (https://github.com/
geoffvasil/nssl_mri).
Analyticandsemi-analyticestimates
Local equatorial calculation.Ourpreliminaryestimatesofthemaxi-
mum poloidal field strength involve solving a simplified equatorial
modelofthefullperturbationequations,settingthediffusionparam-
eters ν, η → 0. Using a Lagrangian displacement vector, ξ, in Eulerian
coordinates
ξ ξ ξ
u u u
∇
∇ ∇
∇
= ∂ + ⋅ − ⋅ , (28)
t 0 0
ξ
b B
∇
∇
= × ( × ). (29)
0
Inlocalcylindricalcoordinatesneartheequator(r, ϕ, z),weassume
all perturbations are axis-symmetric and depend harmonically
∝e k z ωt
i( − )
z
. The cylindrical assumption simplifies the analytical
7. calculationswhileallowingatransferenceofrelevantquantitiesfrom
themorecomprehensivesphericalmodel.Thatis,weassumeapurely
poloidalbackgroundfieldwiththesameradialformasthefullspher-
ical computations, B0 = Bz(r)ez. We use the same radial density and
angularrotationprofiles,ignoringlatitudinaldependence.Theradial
displacement, ξr, determines all other dynamical quantities,
ξ
ω Ω
ω k v
ξ
= −
2i
−
, (30)
ϕ
z
r
2 2
A
2
ξ
k r ρ
rρ ξ
r
=
i d( )
d
(31)
z
z
r
0
0
ϖ v
B
B
ξ
ω
k r ρ
rρ ξ
r
=
′
+
d( )
d
, (32)
z
z
r
z
r
A
2
2
2
0
0
wherev r B r ρ r
( ) = ( )/ 4π ( )
z
A 0
. The radial momentum equation gives a
second-ordertwo-pointboundary-valueproblemforξr(r).Theresult-
ing real-valued differential equation depends on ω2
; the instability
transitionsdirectlyfromoscillationstoexponentialgrowthwhenω = 0.
Weeliminatetermscontainingξ r
′( )
r
withtheLiouvilletransformation
Ψ r r B r ξ r
( ) = ( ) ( )
z r
. The system for the critical magnetic field reduces
to a Schrödinger-type equation,
Ψ r k Ψ r V r Ψ r
− ″( ) + ( ) + ( ) ( ) = 0, (33)
z
2
with boundary conditions
Ψ r r Ψ r r
( = ) = ( = ) = 0 (34)
0 1
and potential,
V
r
v
Ω
r
rρ
B r rρ
B
r r
=
d
d
+
d
d
1 d
d
+
3
4
. (35)
z
z
A
2
2
0
0
2
Upper bound. The maximum background field strength occurs in
thelimitkz → 0.WithfixedfunctionalformsforΩ(r),ρ0(r),wesuppose
B r B
r r
r r
( ) =
1 + 4( / )
5( / )
, (36)
z 1
1
5
1
3
withB1 = Bz(r1)settingandoverallamplitudeand B
1/ 1
2
servingasagen-
eralized eigenvalue parameter. We solve the resulting system with
DedalususingbothChebyshevandLegendreseriesfor64,128and256
spectral modes, all yielding the same result, B1 = 1,070 G. The results
are also insensitive to detailed changes in the functional form of the
background profile.
Growth rate. We use a simplified formula for the MRI exponen-
tial growth, proportional to eγt
, in a regime not extremely far above
onset22
.Thatis,
γ
α ω ΩS ω α
ω Ω
≈
(2 − (1 + ))
+ 4
, (37)
2
2
A
2
A
2 2
A
2 2
where α = 2H/L ≈ 0.2–0.3 is the mode aspect ratio with latitudinal
wavelength,L ≈ 20°–30°R⊙,andNSSLdepthH ≈ 0.05R⊙.Themaintext
defines all other parameters. In the NSSL, S ≈ Ω. Therefore, γ/Ω ≈ 0.1,
whenα ≈ 0.3andωA/Ω ≈ 1;andγ/Ω ≈ 0.01,whenα ≈ 0.2andωA/Ω ≈ 0.1.
Saturation amplitude.Weusenon-dissipativequasi-lineartheory22
to
estimate the amplitude of the overall saturation. In a finite-thickness
domain, the MRI saturates by transporting mean magnetic flux and
angularmomentumradially.Bothquantitiesare(approximately)glob-
allyconserved;however,theinstabilityshiftsthemagneticfluxinward
andangularmomentumoutward,sothepotentialfromequation(35)
ispositiveeverywhereinthedomain.
Given the cylindrical radius, r, the local angular momentum and
magnetic flux density
L ρ ru M ρ ra
= , = . (38)
ϕ ϕ
0 0
The respective local flux transport
L L r b
∇
∇ ∇
∇
∂ + ⋅ ( ) = ⋅ ( ), (39)
t ϕ
u b
u
M M
∇
∇
∂ + ⋅ ( ) = 0. (40)
t
For quadratic-order feedback,
ρ r δu r b b ρ u u r b b ρ u u
∂ ( ) = ∂ ( ( − )) + ∂ ( ( − )), (41)
t ϕ r ϕ r ϕ r z ϕ z ϕ z
0
2 2
0
2
0
ρ r δa r ρ a u r ρ a u
∂ ( ) = − ∂ ( ) − ∂ ( ). (42)
t ϕ r ϕ r z ϕ z
0
2 2
0
2
0
For linear meridional perturbations,
u ψ u
rρ ψ
rρ
= − ∂ , =
∂ ( )
, (43)
r z z
r 0
0
b a b
ra
r
= − ∂ , =
∂ ( )
. (44)
r z ϕ z
r ϕ
For the angular components,
u Ω S ψ
B
ρ
b
∂ = ∂ (2 − ) +
4π
, (45)
t ϕ z
z
ϕ
0
a B ψ
∂ = ∂ ( ), (46)
t ϕ z z
b B u S a
∂ = ∂ ( + ). (47)
t ϕ z z ϕ ϕ
Usingthelinearbalances,wetimeintegratetoobtainthelatitudinal-
mean rotational and magnetic feedback,
L
δΩ
r ρ
r ρ
=
1
∂ ( ), (48)
r
3
0
2
0
δA
r ρ
r ρ
=
1
∂ ( Φ). (49)
r
2
0
2
0
where angle brackets represent z averages and
L
B a u Ω S a
B
=
2 ⟨ ⟩ − (2 − ) ⟨ ⟩
2
, (50)
z ϕ ϕ ϕ
z
2
2
a
B
Φ =
⟨ ⟩
2
. (51)
ϕ
z
2
The dynamic shear and magnetic corrections,
δS r δΩ δB
r
rδA
= − ∂ , =
1
∂ ( ). (52)
r z r
8. Article
We derive an overall amplitude estimate by considering the
functional
∫ V Ψ Ψ r
∇
∇
= ( + )d , (53)
2 2
F
whichresultsfromintegratingequation(33)withrespecttoΨ*(r).The
saturation condition is
F F
δ = − . (54)
The left-hand side includes all linear-order perturbations in the
potential, δV, and wavefunction, δΨ, where
δV
r
v
ΩδΩ
r
δB
B
r
v
Ω
r
rρ
B r rρ
δB
r
δB
B
rρ
B r rρ
B
r
=
2 d( )
d
− 2
d
d
+
d
d
1 d
d
−
d
d
1 d
d
,
(55)
z
z
z
z z
z z
z
A
2
A
2
2
0
0
0
0
δΨ
δB
B
Ψ
= . (56)
z
z
Allreferenceandperturbationquantitiesderivefromthefullsphere
numerical eigenmode calculation. We translate to cylindrical coor-
dinates by approximating z averages with latitudinal θ averages. The
sphericaleigenmodeslocalizeneartheequator,andtheNSSLthickness
isonlyabout5%ofthesolarradius,justifyingthecylindricalapproxi-
mation in the amplitude estimate.
Empirically, the first δV term dominates the overall feedback cal-
culation,owingtotheshearcorrections δΩ r H
∝d /d ~ 1/ r
2
.Isolatingthe
shear effect produces the simple phenomenological formula in
equation (3).
NSSLenergeticsandturbulenceparameterization
We estimate that the order-of-magnitude energetics of the NSSL are
consistentwiththeamplitudesoftorsionaloscillations.Thetorsional
oscillations comprise |Ω′| ≈ 1 nHz rotational perturbation, relative to
the Ω0 ≈ 466 nHz equatorial frame rotation rate. However, the NSSL
contains ΔΩ ≈ 11 nHz mean rotational shear estimated from the func-
tionalforminequations(10)–(13).Intermsofvelocities,theshearinthe
NSSL has a peak contrast of roughly U0 ≈ 5 × 103
cm s−1
across a length
scaleL0 ≈ 0.06R⊙.Therelativeamplitudesofthetorsionaloscillations
to the NSSL background, |Ω′|/ΔΩ, are thus about 10%. Meanwhile, the
radial and latitudinal global differential rotations have amplitudes of
the order of about 100 nHz. The relative energies are approximately
thesquaresofthese,implyingthattheΔKEofthetorsionaloscillations
is about 0.01% to the differential rotation and about 1% to the NSSL.
TheseroughestimatesshowthattheNSSLandthedifferentialrotation
can provide ample energy reservoirs for driving an MRI dynamo, and
theamplitudeofthetorsionaloscillationsisconsistentwithnonlinear
responses seen in classical convection-zone dynamos17
.
Vigoroushydrodynamicconvectiveturbulenceprobablyestablishes
thedifferentialrotationoftheNSSL.Thelargereservoirofshearinthe
solarinteriorplaystheanaloguepartofgravityandKeplerianshearin
accretiondisks.Thedetailsofsolarconvectionareneitherwellunder-
stood nor well constrained by observations. There are indications,
however, that the maintenance of the NSSL is separate from the solar
cycle because neither the global differential rotation nor the NSSL
shows substantial changes during the solar cycle other than in the
torsional oscillations.
StrongdynamicalturbulenceintheouterlayersoftheSunisanuncer-
taintyofourMRIdynamoframework,butscaleseparationgiveshope
for progress. From our linear instability calculations, the solar MRI
operates relatively close to the onset and happens predominantly on
large scales. If the fast turbulence of the outer layers of the Sun acts
mainly as an enhanced dissipation, then the solar MRI should survive
relativelyunaffected.Treatingscale-separateddynamicsinthisfashion
hasgoodprecedent:large-scalebaroclinicinstabilityintheatmosphere
ofEarthgracefullyploughsthroughthevigorousmoisttropospheric
convection(thunderstorms).Scale-separateddynamicsareparticularly
relevant because the MRI represents a type of essentially nonlinear
dynamo,whichcyclicallyreconfiguresanexistingmagneticfieldusing
kineticenergyasacatalyst.Frompreviouswork,itisclearthatthedeep
solarconvectionzonecanproduceglobal-scalefields,butthesefields
generally have properties very different from the observed fields17
.
EssentiallynonlinearMHDdynamoshaveanaloguesinpipeturbulence,
and, similar to those systems, the self-sustaining process leads to an
attractor in which the dynamo settles into a cyclic state independent
of its beginnings.
A full nonlinear treatment of turbulence in the NSSL-MRI setting
awaitsfuturework.Hereweadoptasimplifiedturbulencemodelusing
enhanced dissipation. To model the effects of turbulence, we assume
thattheviscousandmagneticdiffusivitiesareenhancedsuchthatthe
turbulentmagneticPrandtlnumberPm = 1(withnoprincipleofturbu-
lencesuggestingotherwise).ThemomentumandmagneticReynolds
numbersareRe = Rm ≈ 1.5 × 103
.Thesevaluesarevastlymoredissipative
than the microphysical properties of solar plasma (that is, Re ~ 1012
),
andthemicrophysicalPm ≪ 1,implyingthatRm ≪ Re.Thestudiescon-
ducted here find relative independence in the MRI on the choices of
Rewithinamodestrange.Bycontrast,otherinstabilities(forexample,
convection) depend strongly on Re. We compute sample simulations
downtoRe ≈ 50withqualitativelysimilarresults,althoughtheymatch
the observed patterns less well and require somewhat stronger back-
ground fields. Our adopted value of Re ≈ 1,500 strikes a good balance
for an extremely under-constrained process. Our turbulent param-
eterizations also produce falsifiable predictions: our proposed MRI
dynamomechanismwouldfaceseverechallengesiffuturehelioseismic
studiesoftheSunsuggestthattheturbulentdissipationismuchlarger
than expected (for example, if the effective Re ≪ 1). However, it is dif-
ficult to imagine how any nonlinear dynamics would happen in this
scenario.
Dataavailability
TheraweigenfunctionandeigenvaluedatausedtogenerateFig.2can
befoundalongwiththeanalysisscriptsatGitHub(https://github.com/
geoffvasil/nssl_mri)39
.
Codeavailability
WeusetheDedaluscodeandadditionalanalysistoolswritteninPython,
as noted and referenced in the Methods. Beyond the main Dedalus
installation, all scripts are available at GitHub (https://github.com/
geoffvasil/nssl_mri)39
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and gravity waves in sound-proof treatments of stellar interiors: II. Lagrangian
constrained analysis. Astrophys. J. 773, 169 (2013).
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Acknowledgements D.L., K.A., K.J.B., J.S.O. and B.P.B. are supported in part by the NASA HTMS
grant 80NSSC20K1280. D.L., K.J.B., J.S.O. and B.P.B. are partly supported by the NASA OSTFL
grant 80NSSC22K1738. N.B. acknowledges support from the NASA grant 80NSSC22M0162.
Computations were conducted with support from the NASA High-End Computing Program
through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center on the
Pleiades supercomputer with allocation GID s2276. Our dear co-author, Keith Julien, passed
away unexpectedly while this paper was in the press. We want to acknowledge the outstanding
friend and colleague he was for so many years. He did much to make this work a reality and
was thrilled to see it completed. He will be sorely missed.
AuthorcontributionsG.M.V., D.L., J.S.O. and K.J. conceived and designed the experiments.
G.M.V. performed analytical and semi-analytical estimates. K.J.B. and D.L. developed the
multidimensional spherical eigenvalue solver used in the computations. K.A. and D.L. performed
and verified the eigenvalue computations. K.J.B., G.M.V., J.S.O., D.L. and B.P.B. contributed to the
numerical simulation and analysis tools. G.M.V., D.L., B.P.B. and J.S.O. wrote and, along with
K.J.B., K.A., K.J. and N.B., revised the paper. All authors participated in discussions around the
experimental methods, results and the Article.
Competing interests The authors declare no competing interests.
Additional information
Correspondence and requests for materials should be addressed to Geoffrey M. Vasil.
Peer review information Nature thanks Steven Balbus and the other, anonymous, reviewer(s)
for their contribution to the peer review of this work.
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