Scientists detected emission lines from the ionized argon hydride (36ArH+) molecule in spectra of the Crab Nebula obtained with the Herschel Space Observatory. The detection of 36ArH+ confirms that argon originated from explosive nucleosynthesis during the core-collapse supernova that created the Crab Nebula. The likely excitation mechanism is electron collisions in partially ionized regions with electron densities of a few hundred per cubic centimeter. This is the first detection of a noble gas molecule in space.
Herschel far infrared_spectroscopy_of_the_galactic_centerSérgio Sacani
The document summarizes observations from the Herschel Space Observatory of the Galactic Center region, focusing on a spectral scan toward Sagittarius A*. Key findings include:
1) Strong emission from atomic fine structure lines and rotationally excited lines of molecules like CO, H2O and HCO+ are detected.
2) The excitation of the CO ladder is consistent with either a hot isothermal gas component at 103.1 K and 104 cm-3, or a distribution of warmer gas at higher densities, with most CO at 300 K.
3) The detected molecular features suggest heating is from a combination of UV irradiation and shocks in the gas, rather than very enhanced X-ray or cosmic
Alma observations of_the_hh46_47_molecular_outflowSérgio Sacani
ALMA observations of the HH 46/47 molecular outflow reveal striking differences between the blue and red lobes. The blue lobe morphology and kinematics are consistent with entrainment by a wide-angle wind, while the red lobe shows a more complex structure with evidence of entrainment by both a wide-angle wind and collimated episodic winds. Three major clumps along the red lobe axis have velocity distributions consistent with prompt entrainment by periodic mass ejection episodes occurring every few hundred years. Position-velocity cuts show velocity gradients increasing toward the outflow axis, inconsistent with outflow rotation.
Propagation of highly_efficient_star_formation_in_ngc7000Sérgio Sacani
This document summarizes a study of star formation in molecular clouds near the H II region NGC 7000. The authors surveyed NH3 and H2O maser emission toward the molecular cloud L935 located near NGC 7000. They identified five dense molecular clumps based on NH3 emission, which have similar gas temperatures but different levels of star formation activity. One clump located near the boundary of the H II region has a high star formation efficiency of 36-62%, suggesting triggered star formation due to its interaction with the expanding H II region.
The document summarizes Spitzer observations of the supernova remnant IC 443. The MIPS images show the remnant's morphology in great detail, resembling a shell or loop. The dust temperature ranges from 18-30 K based on the 70/160um ratio. IRS spectroscopy confirms shock-excited atomic and molecular emission, with shock velocities of 60-90 km/s. H2 excitation diagrams show temperatures of 300-600 K and column densities varying across the remnant.
An elevation of 0.1 light-seconds for the optical jet base in an accreting Ga...Sérgio Sacani
Relativistic plasma jets are observed in many systems that
host accreting black holes. According to theory, coiled magnetic
fields close to the black hole accelerate and collimate the
plasma, leading to a jet being launched1–3. Isolating emission
from this acceleration and collimation zone is key to measuring
its size and understanding jet formation physics. But this
is challenging because emission from the jet base cannot
easily be disentangled from other accreting components. Here,
we show that rapid optical flux variations from an accreting
Galactic black-hole binary are delayed with respect to X-rays
radiated from close to the black hole by about 0.1 seconds, and
that this delayed signal appears together with a brightening
radio jet. The origin of these subsecond optical variations
has hitherto been controversial4–8. Not only does our work
strongly support a jet origin for the optical variations but it
also sets a characteristic elevation of ≲ 103 Schwarzschild
radii for the main inner optical emission zone above the black
hole9, constraining both internal shock10 and magnetohydrodynamic11
models. Similarities with blazars12,13 suggest that jet
structure and launching physics could potentially be unified
under mass-invariant models. Two of the best-studied jetted
black-hole binaries show very similar optical lags8,14,15, so this
size scale may be a defining feature of such systems.
A new universal formula for atoms, planets, and galaxiesIOSR Journals
In this paper a new universal formula about the rotation velocity distribution of atoms, planets, and galaxies is presented. It is based on a new general formula based on the relativistic Schwarzschild/Minkowski metric, where it has been possible to obtain expressions for the rotation velocity - and mass distribution versus the distance to the atomic nucleus, planet system centre, and galactic centre. A mathematical proof of this new formula is also given. This formula is divided into a Keplerian(general relativity)-and a relativistic(special relativity) part. For the atomic-and planet systems the Keplerian distribution is followed, which is also in accordance with observations.
According to the rotation velocity distribution of the galaxies the rotation velocity increases very rapidly from the centre and reaches a plateau which is constant out to a great distance from the centre. This is in accordance with observations and is also in accordance with the main structure of rotation velocity versus distance from different galaxy measurements.
Computer simulations were also performed to establish and verify the rotation velocity distributions in the atomic – planetary- and galaxy system, according to this paper. These computer simulations are in accordance with observations in two and three dimensions. It was also possible to study the matching percentage in these calculations showing a much higher matching percentage between theoretical and observational values by this new formula.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
Herschel far infrared_spectroscopy_of_the_galactic_centerSérgio Sacani
The document summarizes observations from the Herschel Space Observatory of the Galactic Center region, focusing on a spectral scan toward Sagittarius A*. Key findings include:
1) Strong emission from atomic fine structure lines and rotationally excited lines of molecules like CO, H2O and HCO+ are detected.
2) The excitation of the CO ladder is consistent with either a hot isothermal gas component at 103.1 K and 104 cm-3, or a distribution of warmer gas at higher densities, with most CO at 300 K.
3) The detected molecular features suggest heating is from a combination of UV irradiation and shocks in the gas, rather than very enhanced X-ray or cosmic
Alma observations of_the_hh46_47_molecular_outflowSérgio Sacani
ALMA observations of the HH 46/47 molecular outflow reveal striking differences between the blue and red lobes. The blue lobe morphology and kinematics are consistent with entrainment by a wide-angle wind, while the red lobe shows a more complex structure with evidence of entrainment by both a wide-angle wind and collimated episodic winds. Three major clumps along the red lobe axis have velocity distributions consistent with prompt entrainment by periodic mass ejection episodes occurring every few hundred years. Position-velocity cuts show velocity gradients increasing toward the outflow axis, inconsistent with outflow rotation.
Propagation of highly_efficient_star_formation_in_ngc7000Sérgio Sacani
This document summarizes a study of star formation in molecular clouds near the H II region NGC 7000. The authors surveyed NH3 and H2O maser emission toward the molecular cloud L935 located near NGC 7000. They identified five dense molecular clumps based on NH3 emission, which have similar gas temperatures but different levels of star formation activity. One clump located near the boundary of the H II region has a high star formation efficiency of 36-62%, suggesting triggered star formation due to its interaction with the expanding H II region.
The document summarizes Spitzer observations of the supernova remnant IC 443. The MIPS images show the remnant's morphology in great detail, resembling a shell or loop. The dust temperature ranges from 18-30 K based on the 70/160um ratio. IRS spectroscopy confirms shock-excited atomic and molecular emission, with shock velocities of 60-90 km/s. H2 excitation diagrams show temperatures of 300-600 K and column densities varying across the remnant.
An elevation of 0.1 light-seconds for the optical jet base in an accreting Ga...Sérgio Sacani
Relativistic plasma jets are observed in many systems that
host accreting black holes. According to theory, coiled magnetic
fields close to the black hole accelerate and collimate the
plasma, leading to a jet being launched1–3. Isolating emission
from this acceleration and collimation zone is key to measuring
its size and understanding jet formation physics. But this
is challenging because emission from the jet base cannot
easily be disentangled from other accreting components. Here,
we show that rapid optical flux variations from an accreting
Galactic black-hole binary are delayed with respect to X-rays
radiated from close to the black hole by about 0.1 seconds, and
that this delayed signal appears together with a brightening
radio jet. The origin of these subsecond optical variations
has hitherto been controversial4–8. Not only does our work
strongly support a jet origin for the optical variations but it
also sets a characteristic elevation of ≲ 103 Schwarzschild
radii for the main inner optical emission zone above the black
hole9, constraining both internal shock10 and magnetohydrodynamic11
models. Similarities with blazars12,13 suggest that jet
structure and launching physics could potentially be unified
under mass-invariant models. Two of the best-studied jetted
black-hole binaries show very similar optical lags8,14,15, so this
size scale may be a defining feature of such systems.
A new universal formula for atoms, planets, and galaxiesIOSR Journals
In this paper a new universal formula about the rotation velocity distribution of atoms, planets, and galaxies is presented. It is based on a new general formula based on the relativistic Schwarzschild/Minkowski metric, where it has been possible to obtain expressions for the rotation velocity - and mass distribution versus the distance to the atomic nucleus, planet system centre, and galactic centre. A mathematical proof of this new formula is also given. This formula is divided into a Keplerian(general relativity)-and a relativistic(special relativity) part. For the atomic-and planet systems the Keplerian distribution is followed, which is also in accordance with observations.
According to the rotation velocity distribution of the galaxies the rotation velocity increases very rapidly from the centre and reaches a plateau which is constant out to a great distance from the centre. This is in accordance with observations and is also in accordance with the main structure of rotation velocity versus distance from different galaxy measurements.
Computer simulations were also performed to establish and verify the rotation velocity distributions in the atomic – planetary- and galaxy system, according to this paper. These computer simulations are in accordance with observations in two and three dimensions. It was also possible to study the matching percentage in these calculations showing a much higher matching percentage between theoretical and observational values by this new formula.
The shadow _of_the_flying_saucer_a_very_low_temperature_for_large_dust_grainsSérgio Sacani
Os astrónomos usaram o ALMA e os telescópios do IRAM para fazer a primeira medição direta da temperatura dos grãos de poeira grandes situados nas regiões periféricas de um disco de formação planetária que se encontra em torno de uma estrela jovem. Ao observar de forma inovadora um objeto cujo nome informal é Disco Voador, os astrónomos descobriram que os grãos de poeira são muito mais frios do que o esperado: -266º Celsius. Este resultado surpreendente sugere que os modelos teóricos destes discos precisam de ser revistos.
Uma equipa internacional liderada por Stephane Guilloteau do Laboratoire d´Astrophysique de Bordeaux, França, mediu a temperatura de enormes grãos de poeira que se encontram em torno da jovem estrela 2MASS J16281370-2431391 na região de formação estelar Rho Ophiuchi, a cerca de 400 anos-luz de distância da Terra.
Esta estrela encontra-se rodeada por um disco de gás e poeira — chamado disco protoplanetário, uma vez que se encontra na fase inicial da formação de um sistema planetário. Este disco é visto de perfil quando observado a partir da Terra e a sua aparência em imagens no visível levou a que se lhe desse o nome informal de Disco Voador.
Os astrónomos utilizaram o ALMA para observar o brilho emitido pelas moléculas de monóxido de carbono no disco da 2MASS J16281370-2431391. As imagens revelaram-se extremamente nítidas e descobriu-se algo estranho — em alguns casos o sinal recebido era negativo. Normalmente um sinal negativo é fisicamente impossível, mas neste caso existe uma explicação, que leva a uma conclusão surpreendente.
X-ray spectroscopy AGN - High-Excitation and Low-Excitation Radio Galaxies: a...Valentina Scipione
1) The study compares X-ray properties of 14 radio galaxies divided into high-excitation (HEG) and low-excitation (LEG) galaxies based on optical emission lines.
2) HEGs have higher average intrinsic neutral hydrogen column densities and X-ray luminosities than LEGs. They also have stronger optical [OIII] emission lines.
3) The distributions of column densities and X-ray luminosities between HEGs and LEGs are bimodal. HEGs also show evidence for accretion disks from detected iron K-alpha lines, which are absent in LEGs.
4) The results suggest LEGs have a less efficient accretion regime than HEGs, possibly only accre
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
Nitrogen Chemistry in Disffuse Interstellar MediumPrince Tiwari
This the project presentation which I gave at the end of VSRP-TIFR programme. It summarizes the study of nitrogen chemistry in diffuse galactic cloud W49N with help of data from HIFI spectrometer on-board Herschel Space Observatory.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
Two gamma ray bursts from dusty regions with little molecular gasGOASA
This document summarizes spatially-resolved observations of two gamma-ray burst (GRB) host galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA detected molecular gas emission and dust continuum emission from the nuclear regions of both hosts. However, for one host (GRB 020819B), the GRB explosion site showed dust continuum emission but no molecular gas detection. This suggests the GRB occurred in a dust-rich region with a shortage of molecular gas, unlike typical star-forming regions. The molecular gas-to-dust ratio at the GRB site was much lower than in the host's nuclear region and the Milky Way, indicating the environment where GRBs occur
An extreme magneto-ionic environment associated with the fast radio burst sou...Sérgio Sacani
Fast radio bursts are millisecond-duration, extragalactic radio
flashes of unknown physical origin1–3. The only known repeating
fast radio burst source4–6—FRB 121102—has been localized to a
star-forming region in a dwarf galaxy7–9 at redshift 0.193 and is
spatially coincident with a compact, persistent radio source7,10.
The origin of the bursts, the nature of the persistent source and
the properties of the local environment are still unclear. Here we
report observations of FRB 121102 that show almost 100 per cent
linearly polarized emission at a very high and variable Faraday
rotation measure in the source frame (varying from +1.46×105
radians per square metre to +1.33 × 105
radians per square
metre at epochs separated by seven months) and narrow (below
30 microseconds) temporal structure. The large and variable
rotation measure demonstrates that FRB 121102 is in an extreme
and dynamic magneto-ionic environment, and the short durations of
the bursts suggest a neutron star origin. Such large rotation measures
have hitherto been observed11,12 only in the vicinities of massive
black holes (larger than about 10,000 solar masses). Indeed, the
properties of the persistent radio source are compatible with those
of a low-luminosity, accreting massive black hole10. The bursts may
therefore come from a neutron star in such an environment or could
be explained by other models, such as a highly magnetized wind
nebula13 or supernova remnant14 surrounding a young neutron star
Gas physical conditions_and_kinematics_of_the_giant_outflow_ou4Sérgio Sacani
This document discusses observations of the giant outflow Ou4, located near the HII region Sh 2-129. Spectroscopic observations of Ou4 reveal shock-excited gas consistent with a fast collimated outflow. Mid-infrared images show a bubble of hot dust emission inside Ou4 that corresponds to [OIII] features. The distance and properties of Ou4 are consistent with it being launched about 90,000 years ago from the young massive star cluster HR 8119, located at the center of Sh 2-129. However, the possibility that Ou4 is a planetary nebula or resulted from an eruptive event on a massive asymptotic giant branch star cannot be ruled out.
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
Detection of the_central_star_of_the_planetary_nebula_ngc6302Sérgio Sacani
This document reports on the first direct detection of the central star of the planetary nebula NGC 6302 using the Wide Field Camera 3 on the Hubble Space Telescope. Photometry of the central star was obtained in two narrowband filters, F469N and F673N, from which the reddening was estimated to be c=3.1, corresponding to AV=6.6 magnitudes of extinction. Comparison to evolutionary tracks suggests the central star has a temperature of around 200,000 K, luminosity of 2000 L☉, and the nebula is around 2,200 years old. The high extinction from dust in the nebula had previously prevented direct detection of the central star.
This document reports the first detection of hydrogen peroxide (HOOH) in interstellar space. Four HOOH transitions were detected toward the ρ Oph A molecular cloud core, including three transitions mapped over the densest part of the core. Analysis of the line intensities using a rotation diagram method derived a HOOH rotation temperature of 22 K and column density of 8×1012 cm-2, corresponding to an abundance relative to H2 of about 1×10-10. This detection provides evidence that HOOH plays a role in oxygen and water chemistry in molecular clouds.
Unexpectedly large mass_loss_during_the_thermal_pulse_cycle_of_the_red_giantSérgio Sacani
1) Observations of the red giant star RSculptoris using ALMA revealed an unexpected spiral structure extending from the central star to its detached dust and gas shell, indicating it is likely a binary system.
2) Hydrodynamic modeling suggests the star underwent a thermal pulse around 1800 years ago, ejecting 0.003 solar masses of material at 14.3 km/s, about 30 times the pre-pulse rate.
3) This challenges existing theories about mass loss during thermal pulses, finding much more mass is lost during and shortly after pulses than previously estimated.
A wide and collimated radio jet in 3C84 on the scale of a few hundred gravita...Sérgio Sacani
This document summarizes key findings from a study of the radio jet in galaxy 3C84 using very long baseline interferometry (VLBI) with the RadioAstron space telescope. The observations resolve the edge-brightened jet structure only 30 microarcseconds from the core, corresponding to ~350 gravitational radii. This is 10 times closer to the central engine than previous ground-based observations. The measurements show the jet has an initially wide opening angle of 130 degrees that rapidly collimates into an almost cylindrical profile out to ~8,000 gravitational radii. The wide jet observed so close to the core poses challenges for models where the jet originates from the black hole ergosphere.
Water vapour absorption_in_the_clear_atmosphere_of_a_neptune_sized_exoplanetSérgio Sacani
This document summarizes research on the transmission spectrum of the exoplanet HAT-P-11b, a Neptune-sized planet. Observations from the Hubble Space Telescope and Spitzer Space Telescope detected water vapor absorption in the planet's atmosphere at a wavelength of 1.4 micrometers. Analysis of the spectrum indicates the atmosphere is predominantly clear down to 1 mbar and has a hydrogen abundance similar to solar values. Atmospheric modeling suggests a metallicity around 190 times that of the Sun's, in agreement with core accretion planet formation theories. This makes HAT-P-11b the smallest exoplanet to date with a detected molecular signature in its atmosphere, providing new insights into the composition and formation of Neptune-sized
Probing the jet_base_of_blazar_pks1830211_from_the_chromatic_variability_of_i...Sérgio Sacani
This document summarizes ALMA observations of the blazar PKS 1830-211 taken over multiple epochs in 2012. The blazar is lensed by a foreground galaxy, producing two resolved images (NE and SW) separated by 1". The observations were taken at frequencies corresponding to 350-1050 GHz in the blazar rest frame. Analysis of the flux ratio between the two images over time and frequency revealed a remarkable frequency-dependent behavior, implying a "chromatic structure" in the blazar jet. This is interpreted as evidence for a "core-shift effect" caused by plasmon ejection very near the base of the jet. The observations provide a unique probe of activity in the region where plasma acceleration occurs in blazar
Evidence of a plume on Europa from Galileo magnetic and plasma wave signaturesSérgio Sacani
The icy surface of Jupiter’s moon, Europa, is thought to lie
on top of a global ocean1–4. Signatures in some Hubble Space
Telescope images have been associated with putative water
plumes rising above Europa’s surface5,6, providing support for
the ocean theory. However, all telescopic detections reported
were made at the limit of sensitivity of the data5–7
, thereby calling
for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from
the magnetic field and plasma wave observations acquired on
Galileo’s closest encounter with the moon. During this flyby,
which dropped below 400 km altitude, the magnetometer8
recorded an approximately 1,000-kilometre-scale field rotation
and a decrease of over 200 nT in field magnitude, and
the Plasma Wave Spectrometer9 registered intense localized
wave emissions indicative of a brief but substantial increase
in plasma density. We show that the location, duration and
variations of the magnetic field and plasma wave measurements
are consistent with the interaction of Jupiter’s corotating
plasma with Europa if a plume with characteristics inferred
from Hubble images were erupting from the region of Europa’s
thermal anomalies. These results provide strong independent
evidence of the presence of plumes at Europa.
Alma observations of_feed_and_feedback_in_nearby_seyfert_galaxiesSérgio Sacani
The ALMA observations of NGC 1433 reveal a nuclear gaseous spiral structure within the central kpc. This spiral winds up into a pseudo-ring at ~200 pc from the center. Near the nucleus, there is intense high-velocity CO emission up to 200 km/s that is interpreted as an outflow, involving 3.6 million solar masses of molecular gas and a flow rate of ~7 solar masses per year. The outflow could be driven by both the central star formation and AGN through its radio jets. Continuum emission at 0.87 mm is detected only at the very center and likely comes from thermal dust emission from the molecular torus expected in this Seyfert 2 galaxy.
- The document derives the second order Friedmann equations from the quantum corrected Raychaudhuri equation (QRE), which includes quantum corrections terms.
- One correction term can be interpreted as dark energy/cosmological constant with the observed density value, providing an explanation for the coincidence problem.
- The other correction term can be interpreted as a radiation term in the early universe that prevents the formation of a big bang singularity and predicts an infinite age for the universe by avoiding a divergence in the Hubble parameter or its derivative at any finite time in the past.
X-ray spectroscopy AGN - High-Excitation and Low-Excitation Radio Galaxies: a...Valentina Scipione
1) The study compares X-ray properties of 14 radio galaxies divided into high-excitation (HEG) and low-excitation (LEG) galaxies based on optical emission lines.
2) HEGs have higher average intrinsic neutral hydrogen column densities and X-ray luminosities than LEGs. They also have stronger optical [OIII] emission lines.
3) The distributions of column densities and X-ray luminosities between HEGs and LEGs are bimodal. HEGs also show evidence for accretion disks from detected iron K-alpha lines, which are absent in LEGs.
4) The results suggest LEGs have a less efficient accretion regime than HEGs, possibly only accre
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
Nitrogen Chemistry in Disffuse Interstellar MediumPrince Tiwari
This the project presentation which I gave at the end of VSRP-TIFR programme. It summarizes the study of nitrogen chemistry in diffuse galactic cloud W49N with help of data from HIFI spectrometer on-board Herschel Space Observatory.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Galaxy dynamics and the mass density of the universeSérgio Sacani
Dynamical evidence accumulated over the
past 20 years has convinced astronomers that luminous matter
in a spiral galaxy constitutes no more than 10% of the mass of
a galaxy. An additional 90% is inferred by its gravitational
effect on luminous material. Here I review recent observations
concerning the distribution of luminous and nonluminous
matter in the Milky Way, in galaxies, and in galaxy clusters.
Observations of neutral hydrogen disks, some extending in
radius several times the optical disk, confirm that a massive
dark halo is a major component of virtually every spiral. A
recent surprise has been the discovery that stellar and gas
motions in ellipticals are enormously complex. To date, only for
a few spheroidal galaxies do the velocities extend far enough to
probe the outer mass distribution. But the diverse kinematics
of inner cores, peripheral to deducing the overall mass distribution,
offer additional evidence that ellipticals have acquired
gas-rich systems after initial formation. Dynamical results are
consistent with a low-density universe, in which the required
dark matter could be baryonic. On smallest scales of galaxies
[10 kiloparsec (kpc); H. = 50 kmsec'lmegaparsec'11 the
luminous matter constitutes only 1% of the closure density. On
scales greater than binary galaxies (i.e., .100 kpc) all systems
indicate a density -10% of the closure density, a density
consistent with the low baryon density in the universe. If
large-scale motions in the universe require a higher mass
density, these motions would constitute the first dynamical
evidence for nonbaryonic matter in a universe of higher
density.
Two gamma ray bursts from dusty regions with little molecular gasGOASA
This document summarizes spatially-resolved observations of two gamma-ray burst (GRB) host galaxies using the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA detected molecular gas emission and dust continuum emission from the nuclear regions of both hosts. However, for one host (GRB 020819B), the GRB explosion site showed dust continuum emission but no molecular gas detection. This suggests the GRB occurred in a dust-rich region with a shortage of molecular gas, unlike typical star-forming regions. The molecular gas-to-dust ratio at the GRB site was much lower than in the host's nuclear region and the Milky Way, indicating the environment where GRBs occur
An extreme magneto-ionic environment associated with the fast radio burst sou...Sérgio Sacani
Fast radio bursts are millisecond-duration, extragalactic radio
flashes of unknown physical origin1–3. The only known repeating
fast radio burst source4–6—FRB 121102—has been localized to a
star-forming region in a dwarf galaxy7–9 at redshift 0.193 and is
spatially coincident with a compact, persistent radio source7,10.
The origin of the bursts, the nature of the persistent source and
the properties of the local environment are still unclear. Here we
report observations of FRB 121102 that show almost 100 per cent
linearly polarized emission at a very high and variable Faraday
rotation measure in the source frame (varying from +1.46×105
radians per square metre to +1.33 × 105
radians per square
metre at epochs separated by seven months) and narrow (below
30 microseconds) temporal structure. The large and variable
rotation measure demonstrates that FRB 121102 is in an extreme
and dynamic magneto-ionic environment, and the short durations of
the bursts suggest a neutron star origin. Such large rotation measures
have hitherto been observed11,12 only in the vicinities of massive
black holes (larger than about 10,000 solar masses). Indeed, the
properties of the persistent radio source are compatible with those
of a low-luminosity, accreting massive black hole10. The bursts may
therefore come from a neutron star in such an environment or could
be explained by other models, such as a highly magnetized wind
nebula13 or supernova remnant14 surrounding a young neutron star
Gas physical conditions_and_kinematics_of_the_giant_outflow_ou4Sérgio Sacani
This document discusses observations of the giant outflow Ou4, located near the HII region Sh 2-129. Spectroscopic observations of Ou4 reveal shock-excited gas consistent with a fast collimated outflow. Mid-infrared images show a bubble of hot dust emission inside Ou4 that corresponds to [OIII] features. The distance and properties of Ou4 are consistent with it being launched about 90,000 years ago from the young massive star cluster HR 8119, located at the center of Sh 2-129. However, the possibility that Ou4 is a planetary nebula or resulted from an eruptive event on a massive asymptotic giant branch star cannot be ruled out.
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
Detection of the_central_star_of_the_planetary_nebula_ngc6302Sérgio Sacani
This document reports on the first direct detection of the central star of the planetary nebula NGC 6302 using the Wide Field Camera 3 on the Hubble Space Telescope. Photometry of the central star was obtained in two narrowband filters, F469N and F673N, from which the reddening was estimated to be c=3.1, corresponding to AV=6.6 magnitudes of extinction. Comparison to evolutionary tracks suggests the central star has a temperature of around 200,000 K, luminosity of 2000 L☉, and the nebula is around 2,200 years old. The high extinction from dust in the nebula had previously prevented direct detection of the central star.
This document reports the first detection of hydrogen peroxide (HOOH) in interstellar space. Four HOOH transitions were detected toward the ρ Oph A molecular cloud core, including three transitions mapped over the densest part of the core. Analysis of the line intensities using a rotation diagram method derived a HOOH rotation temperature of 22 K and column density of 8×1012 cm-2, corresponding to an abundance relative to H2 of about 1×10-10. This detection provides evidence that HOOH plays a role in oxygen and water chemistry in molecular clouds.
Unexpectedly large mass_loss_during_the_thermal_pulse_cycle_of_the_red_giantSérgio Sacani
1) Observations of the red giant star RSculptoris using ALMA revealed an unexpected spiral structure extending from the central star to its detached dust and gas shell, indicating it is likely a binary system.
2) Hydrodynamic modeling suggests the star underwent a thermal pulse around 1800 years ago, ejecting 0.003 solar masses of material at 14.3 km/s, about 30 times the pre-pulse rate.
3) This challenges existing theories about mass loss during thermal pulses, finding much more mass is lost during and shortly after pulses than previously estimated.
A wide and collimated radio jet in 3C84 on the scale of a few hundred gravita...Sérgio Sacani
This document summarizes key findings from a study of the radio jet in galaxy 3C84 using very long baseline interferometry (VLBI) with the RadioAstron space telescope. The observations resolve the edge-brightened jet structure only 30 microarcseconds from the core, corresponding to ~350 gravitational radii. This is 10 times closer to the central engine than previous ground-based observations. The measurements show the jet has an initially wide opening angle of 130 degrees that rapidly collimates into an almost cylindrical profile out to ~8,000 gravitational radii. The wide jet observed so close to the core poses challenges for models where the jet originates from the black hole ergosphere.
Water vapour absorption_in_the_clear_atmosphere_of_a_neptune_sized_exoplanetSérgio Sacani
This document summarizes research on the transmission spectrum of the exoplanet HAT-P-11b, a Neptune-sized planet. Observations from the Hubble Space Telescope and Spitzer Space Telescope detected water vapor absorption in the planet's atmosphere at a wavelength of 1.4 micrometers. Analysis of the spectrum indicates the atmosphere is predominantly clear down to 1 mbar and has a hydrogen abundance similar to solar values. Atmospheric modeling suggests a metallicity around 190 times that of the Sun's, in agreement with core accretion planet formation theories. This makes HAT-P-11b the smallest exoplanet to date with a detected molecular signature in its atmosphere, providing new insights into the composition and formation of Neptune-sized
Probing the jet_base_of_blazar_pks1830211_from_the_chromatic_variability_of_i...Sérgio Sacani
This document summarizes ALMA observations of the blazar PKS 1830-211 taken over multiple epochs in 2012. The blazar is lensed by a foreground galaxy, producing two resolved images (NE and SW) separated by 1". The observations were taken at frequencies corresponding to 350-1050 GHz in the blazar rest frame. Analysis of the flux ratio between the two images over time and frequency revealed a remarkable frequency-dependent behavior, implying a "chromatic structure" in the blazar jet. This is interpreted as evidence for a "core-shift effect" caused by plasmon ejection very near the base of the jet. The observations provide a unique probe of activity in the region where plasma acceleration occurs in blazar
Evidence of a plume on Europa from Galileo magnetic and plasma wave signaturesSérgio Sacani
The icy surface of Jupiter’s moon, Europa, is thought to lie
on top of a global ocean1–4. Signatures in some Hubble Space
Telescope images have been associated with putative water
plumes rising above Europa’s surface5,6, providing support for
the ocean theory. However, all telescopic detections reported
were made at the limit of sensitivity of the data5–7
, thereby calling
for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from
the magnetic field and plasma wave observations acquired on
Galileo’s closest encounter with the moon. During this flyby,
which dropped below 400 km altitude, the magnetometer8
recorded an approximately 1,000-kilometre-scale field rotation
and a decrease of over 200 nT in field magnitude, and
the Plasma Wave Spectrometer9 registered intense localized
wave emissions indicative of a brief but substantial increase
in plasma density. We show that the location, duration and
variations of the magnetic field and plasma wave measurements
are consistent with the interaction of Jupiter’s corotating
plasma with Europa if a plume with characteristics inferred
from Hubble images were erupting from the region of Europa’s
thermal anomalies. These results provide strong independent
evidence of the presence of plumes at Europa.
Alma observations of_feed_and_feedback_in_nearby_seyfert_galaxiesSérgio Sacani
The ALMA observations of NGC 1433 reveal a nuclear gaseous spiral structure within the central kpc. This spiral winds up into a pseudo-ring at ~200 pc from the center. Near the nucleus, there is intense high-velocity CO emission up to 200 km/s that is interpreted as an outflow, involving 3.6 million solar masses of molecular gas and a flow rate of ~7 solar masses per year. The outflow could be driven by both the central star formation and AGN through its radio jets. Continuum emission at 0.87 mm is detected only at the very center and likely comes from thermal dust emission from the molecular torus expected in this Seyfert 2 galaxy.
- The document derives the second order Friedmann equations from the quantum corrected Raychaudhuri equation (QRE), which includes quantum corrections terms.
- One correction term can be interpreted as dark energy/cosmological constant with the observed density value, providing an explanation for the coincidence problem.
- The other correction term can be interpreted as a radiation term in the early universe that prevents the formation of a big bang singularity and predicts an infinite age for the universe by avoiding a divergence in the Hubble parameter or its derivative at any finite time in the past.
This document summarizes observations of the W49 giant molecular cloud (GMC) using the PMO 14m telescope and the Submillimeter Array (SMA). The PMO observations mapped the entire GMC in various molecular lines at scales up to 113 pc, while the SMA mosaic mapped the central star-forming region W49N at scales down to 0.5 pc. The observations are used to derive the mass structure of the GMC across all scales. The main findings are that the W49 GMC has a total gas mass of 1.1 million solar masses within 60 pc and 2x10^5 solar masses within 6 pc. The mass is distributed in a hierarchical network of filaments converging toward the central
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
This document presents a sample of 20 extremely luminous galaxies discovered by the Wide-field Infrared Survey Explorer (WISE). Five of these galaxies have infrared luminosities exceeding 1014 solar luminosities, the highest infrared luminosity threshold yet observed. They were selected using criteria requiring weak or no detection in the first two WISE bands but strong detections in the third and fourth bands. Spectral energy distribution modeling suggests their high luminosities are powered by obscured active galactic nuclei with hot dust temperatures around 450 Kelvin. The existence of such luminous galaxies at redshifts above 3 provides constraints on the early growth of supermassive black holes through rapid accretion.
A vlt flames_survey_for_massive_binaries_in_westerlund_1Sérgio Sacani
1) The authors conducted a radial velocity survey of stars in the young massive cluster Westerlund 1 to search for a potential pre-supernova companion to the magnetar CXO J1647-10.2-455216 located within the cluster.
2) They identified a candidate star, Wd1-5, that has anomalous velocities compared to other stars in the cluster, suggesting it was impacted by the supernova that created the magnetar.
3) Analysis of Wd1-5 found evidence of chemical enrichment that is difficult to explain by single star evolution, but could be explained if Wd1-5 was once part of a close binary system where it accreted material from
An ultraluminous quasar_with_a_twelve_billion_solar_mass_black_hole_at_redshi...Sérgio Sacani
1) Researchers discovered an ultraluminous quasar, SDSS J010013.021280225.8, at a redshift of 6.30, making it the most distant and luminous quasar known.
2) Spectral analysis estimates the black hole at its center has a mass of 1.2 billion solar masses, consistent with an Eddington-limited accretion rate.
3) The quasar has an ionized proximity zone estimated to be 26 million light years across, significantly larger than found for other high-redshift quasars, suggesting its high luminosity.
The document summarizes findings from the Microwave Instrument on the Rosetta Orbiter (MIRO) regarding the subsurface properties and early activity of comet 67P/Churyumov-Gerasimenko. Key points:
- MIRO detected water vapor emissions from the comet beginning in early June 2014 and measured the total water production rate, which varied from 0.3 kg/s to 1.2 kg/s between June and August.
- Water outgassing displayed periodic variations correlated with the comet's 12.4-hour rotation period and seemed to originate primarily from the comet's "neck" region.
- Subsurface temperatures measured by MIRO showed seasonal and diurnal variations, indicating radiation
Assymetries in core_collapse_supernovae_from_maps_of_radioactive_ti_in_cassio...Sérgio Sacani
The document summarizes findings from observations of Cassiopeia A using the Nuclear Spectroscopic Telescope Array (NuSTAR).
1) NuSTAR detected two clear emission lines from the decay of radioactive titanium-44, confirming previous measurements of titanium-44 yield with high significance. The spatial distribution of titanium-44 emission shows it is clumpy and extended along the jet axis seen in X-ray images, with knots off the jet axis.
2) There is no correlation between the distribution of titanium-44 and iron detected by Chandra X-ray Observatory. This suggests much of the iron-rich ejecta has not been shock-heated and is "invisible", constraining models of the remnant.
Detection of an_unidentified_emission_line_in_the_stacked_xray_spectrum_of_ga...Sérgio Sacani
This document describes the detection of an unidentified emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. The line was detected at an energy of 3.55-3.57 keV in independent analyses of the MOS and PN instruments. The line was also seen in Chandra observations of the Perseus cluster. Possible explanations discussed include an atomic transition in thermal plasma, or the decay of sterile neutrino dark matter particles. However, the origin is unclear and requires further observation.
A candidate sub-parsec binary black hole in the Seyfert galaxy NGC 7674Sérgio Sacani
The existence of binary supermassive black holes (SBHs) is predicted by models of hierarchical galaxy formation. To date, only
a single binary SBH has been imaged, at a projected separation of 7.3 pc. Here, we report the detection of a candidate dual SBH
with projected separation of 0.35 pc in the gas-rich interacting spiral galaxy NGC 7674 (Mrk 533). This peculiar Seyfert galaxy
possesses a roughly 0.7 kpc Z-shaped radio jet. The leading model for the formation of such sources postulates the presence of
an uncoalesced binary SBH created during the infall of a satellite galaxy. Using very long baseline interferometry, we imaged
the central region of Mrk 533 at radio frequencies of 2, 5, 8 and 15 GHz. Two, possibly inverted-spectrum, radio cores were
detected at 15 GHz only. The 8–15 GHz spectral indices of the two cores were ≥−0.33 and ≥−0.38 (±30%), consistent with
accreting SBHs. We derived a jet speed of around 0.28c from multi-epoch parsec-scale data of the hotspot region and a source
age of ≥ 8.2 × 103
years.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
An excess of dusty starbursts related to the Spiderweb galaxyGOASA
This document summarizes a study that used the LABOCA instrument on the APEX telescope to observe a field around the high-redshift radio galaxy MRC1138-262 at z=2.16. 16 submillimeter galaxies (SMGs) were detected in the field, with fluxes between 3-11 mJy, indicating a density up to 4 times higher than blank field surveys. Photometric redshifts using Herschel, Spitzer, and VLT data show that at least 8 of the SMGs have z~2.2 and are part of the protocluster associated with MRC1138-262. This corresponds to a star formation rate density 1500 times higher than blank fields at this redshift, concentrated
Magnetic fields and relativistic electrons fill entire galaxy clusterSérgio Sacani
- The authors analyzed deep LOFAR radio observations of the galaxy cluster Abell 2255, detecting radio synchrotron emission distributed over an unprecedented scale of at least 5 megaparsecs, well beyond the cluster outskirts.
- This pervasive radio emission indicates that shocks and turbulence efficiently transfer kinetic energy into relativistic particles and magnetic fields throughout the cluster, including the periphery.
- The strength of the emission requires magnetic field energy densities at least 100 times higher than expected from simple compression of primordial fields, suggesting efficient dynamo action even in the cluster outskirts.
ALMA Observations of the Extraordinary Carina Pillars: A Complementary SampleSérgio Sacani
We present a study of six dusty and gaseous pillars (containing the HH 1004 and HH 1010 objects)
and globules (that contain the HH 666, HH 900, HH 1006, and HH 1066 objects) localized in the Carina
nebula using sensitive and high angular resolution (∼0.3′′) Atacama Large Millimeter/Sub-millimeter
Array (ALMA) observations. This is a more extensive study that the one presented in Cortes-Rangel
et al. (2020). As in this former study, we also analyzed the 1.3 mm continuum emission and C18O(2−1),
N2D+(3−2) and 12CO(2−1) spectral lines. These new observations revealed the molecular outflows
emanating from the pillars, the dusty envelopes+disks that are exciting them, and the extended HH
objects far from their respective pillars. We reveal that the masses of the disks+envelopes are in a
range of 0.02 to 0.38 M⊙, and those for the molecular outflows are of the order of 10−3 M⊙, which
suggests that their exciting sources might be low- or intermediate-mass protostars as already revealed
in recent studies at infrared and submillimeter bands. In the regions associated with the objects HH
900 and HH 1004, we report multiple millimeter continuum sources, from where several molecular
outflows emanate.
Resolved imaging confirms a radiation belt around an ultracool dwarfSérgio Sacani
Radiation belts are present in all large-scale Solar System planetary
30 magnetospheres: Earth, Jupiter, Saturn, Uranus, and Neptune1. These persistent
31 equatorial zones of relativistic particles up to tens of MeV in energy can extend farther
32 than 10 times the planet’s radius, emit gradually varying radio emissions2–4 and impact
33 the surface chemistry of close-in moons5. Recent observations demonstrate that very low
34 mass stars and brown dwarfs, collectively known as ultracool dwarfs, can produce planet35
like radio emissions such as periodically bursting aurorae6–8 from large-scale
36 magnetospheric currents9–11. They also exhibit slowly varying quiescent radio
37 emissions7,12,13 hypothesized to trace low-level coronal flaring14,15 despite departing from
38 empirical multi-wavelength flare relationships8,15. Here we present high resolution
39 imaging of the ultracool dwarf LSR J1835+3259 at 8.4 GHz demonstrating that its
40 quiescent radio emission is spatially resolved and traces a double-lobed and axisymmetric
41 structure similar in morphology to the Jovian radiation belts. Up to 18 ultracool dwarf
42 radii separate the two lobes, which are stably present in three observations spanning
43 more than one year. For plasma confined by the magnetic dipole of LSR J1835+3259, we
44 estimate 15 MeV electron energies consistent with Jupiter’s radiation belts4. Our results
45 confirm recent predictions of radiation belts at both ends of the stellar mass sequence8,16–
46 19 and support broader re-examination of rotating magnetic dipoles in producing non47
thermal quiescent radio emissions from brown dwarfs7, fully convective M dwarfs20, and
4
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
A density cusp of quiescent X-ray binaries in the central parsec of the GalaxySérgio Sacani
The existence of a ‘density cusp’1,2—a localized increase in
number—of stellar-mass black holes near a supermassive black
hole is a fundamental prediction of galactic stellar dynamics3
. The
best place to detect such a cusp is in the Galactic Centre, where
the nearest supermassive black hole, Sagittarius A*, resides. As
many as 20,000 black holes are predicted to settle into the central
parsec of the Galaxy as a result of dynamical friction3–5; however,
so far no density cusp of black holes has been detected. Low-mass
X-ray binary systems that contain a stellar-mass black hole are
natural tracers of isolated black holes. Here we report observations
of a dozen quiescent X-ray binaries in a density cusp within one
parsec of Sagittarius A*. The lower-energy emission spectra that
we observed in these binaries is distinct from the higher-energy
spectra associated with the population of accreting white dwarfs that
dominates the central eight parsecs of the Galaxy6
. The properties
of these X-ray binaries, in particular their spatial distribution and
luminosity function, suggest the existence of hundreds of binary
systems in the central parsec of the Galaxy and many more isolated
black holes. We cannot rule out a contribution to the observed
emission from a population (of up to about one-half the number of
X-ray binaries) of rotationally powered, millisecond pulsars. The
spatial distribution of the binary systems is a relic of their formation
history, either in the stellar disk around Sagittarius A* (ref. 7) or
through in-fall from globular clusters, and constrains the number
density of sources in the modelling of gravitational waves from
massive stellar remnants8,9
, such as neutron stars and black holes.
Dense m agnetized_plasma_associated_with_afast_radio_burstSérgio Sacani
Astrônomos detectaram uma chamada rápida explosão de rádio a cerca de 6 bilhões de anos-luz de distância, uma das menos de duas dezenas desse tipo de evento descobertos nos últimos dez anos, e dessa vez eles têm pistas sobre a fonte.
As rápidas explosões de rádio, ou FRBs, são misteriosas explosões de energia que ocorrem no espaço e que aparecem como rápidos flashes de ondas de rádio nos telescópios da Terra. Essas explosões têm intrigado os astrônomos desde que elas foram reportadas pela primeira vez a uma década atrás. Embora somente 16 dessas explosões tenham sido registradas, eles acreditam que possam existir milhares delas por dia.
Vasculhando mais de 650 horas de dados obtidos pelo Telescópio Green Bank, do NRAO, um grupo internacional de astrônomos descobriu o mais detalhado registro já feito até hoje de uma FRB.
Galaxy growth in a massive halo in the first billion years of cosmic historySérgio Sacani
According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field1–3. Observing these structures during their period of active growth and assembly—the first few hundred million years of the Universe—is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far4,5. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey6. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe7. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.
Swiging between rotation_and_accretion_power_in_a_millisecond_binary_pulsarSérgio Sacani
This document discusses the discovery of a millisecond X-ray pulsar, IGR J18245-2452, located in the globular cluster M28. The pulsar was previously known as the radio millisecond pulsar PSR J1824-2452I. Observations found that the pulsar alternates between accretion-powered and rotation-powered states on timescales of years, providing direct evidence that these two states cycle in recycled pulsars. When accreting, the pulsar shows X-ray pulsations and luminosity characteristic of other accreting millisecond pulsars. When not accreting, it had previously been detected as a radio pulsar. This demonstrates the evolutionary link between low-mass X
Radio continum emission_of_35_edge_on_galaxies_observed_with_the_vlaSérgio Sacani
Usando um dos maiores rádio observatórios do mundo, o Very Large Array do National Radio Astronomy, um grupo de astrônomos descobriram que os halos ao redor dos discos das galáxias espirais são muito mais comuns do que se pensava anteriormente.
A equipe, dirigida pela Dra. Judith Irwin, da Universidade de Queens, em Kingston, ON, Canadá, observou 35 galáxias espirais próximas de lado, de 11 a 137 milhões de anos-luz de distância da Terra.
As galáxias espirais, como a nossa própria Via Láctea ou a famosa Galáxia de Andrômeda, possuem uma vasta maioria de suas estrelas, gás, e poeira num disco plano em rotação com braços espirais. A maior parte da luz e das ondas de rádio observadas com telescópios veem de objetos localizados nesse disco.
“Nós sabíamos antes que alguns halos existiam, mas, usando o poder total do VLA atualizado e o poder total de algumas técnicas de processamento de imagens, nós descobrimos que esses halos são muito mais comuns entre as galáxias espirais do que nós pensávamos antes”, explicou a Dra. Irwin.
A precise measurement of the magnetic field in the corona of the black hole b...Sérgio Sacani
Observations of binary stars containing an accreting black hole or neutron star often show
x-ray emission extending to high energies (>10 kilo–electron volts), which is ascribed to
an accretion disk corona of energetic particles akin to those seen in the solar corona.
Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly
constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the
Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its
2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the
corona. This measurement is substantially lower than previous estimates for such systems,
providing constraints on physical models of accretion physics in black hole and neutron
star binary systems.
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
A precise measurement of the magnetic field in the corona of the black hole b...Sérgio Sacani
Observations of binary stars containing an accreting black hole or neutron star often show
x-ray emission extending to high energies (>10 kilo–electron volts), which is ascribed to
an accretion disk corona of energetic particles akin to those seen in the solar corona.
Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly
constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the
Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its
2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the
corona. This measurement is substantially lower than previous estimates for such systems,
providing constraints on physical models of accretion physics in black hole and neutron
star binary systems.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
Alma observations of_feeding_and_feedback_in_nearby_seyfert_galaxies_outflow_...Sérgio Sacani
ALMA observations of the Seyfert 2 galaxy NGC 1433 reveal a nuclear gaseous spiral structure within a nuclear ring encircling a nuclear stellar bar. Near the nucleus, there is intense high-velocity CO emission interpreted as an AGN-driven molecular outflow. The outflow involves a molecular mass of 3.6 million solar masses and a flow rate of about 7 solar masses per year. Continuum emission at the center is likely thermal dust emission from a molecular torus expected in this Seyfert 2 galaxy. The observations probe gas dynamics within 24 parsecs of the active galactic nucleus.
Detection of the_central_star_of_the_planetary_nebula_ngc_6302Sérgio Sacani
The document summarizes the detection of the central star of the planetary nebula NGC 6302 using new observations from the Hubble Space Telescope's Wide Field Camera 3. Key points:
1) The central star is directly detected for the first time at the center of the nebula, confirming its location but not at the center of the inner dust torus.
2) Photometry of the central star yields a reddening value of c=3.1, corresponding to AV=6.6 magnitudes of extinction, mostly from circumstellar dust.
3) Estimates of the stellar temperature, luminosity, and distance suggest a fairly massive central star of around 0.64 solar masses that is evolving rapidly and fading over time
1. The document describes a new method for selecting dust-reddened quasars that are radio quiet using data from the Wide-Field Infrared Survey Explorer (WISE). The selection process involves identifying bright objects in WISE that have color ratios consistent with quasars, and then visually inspecting archival images to identify point sources.
2. This new selection method identified 12 potential radio-quiet, dust-reddened quasars. Optical and infrared spectra were obtained for these objects using the Keck and NASA IRTF telescopes. Redshifts were calculated by identifying emission lines and their wavelengths.
3. BPT diagrams using emission line ratios identified 5 of the 8 objects as quasars, providing a sample of
The ionized nebula_surrounding_the_w26_in_westerlund_1Sérgio Sacani
The document summarizes observations of an ionized nebula surrounding the red supergiant star W26 in the massive star cluster Westerlund 1. H-alpha images reveal a circumstellar shell or ring 0.1 pc in diameter surrounding the star, as well as a triangular nebula 0.2 pc away with a complex filamentary structure. Spectroscopy confirms the nebula is ionized but the excitation mechanism is unclear given red supergiants do not produce ionizing photons. The nebula and star's high luminosity and spectral variability suggest W26 is a highly evolved red supergiant experiencing extreme mass loss, making it an important case study for understanding the late stages of massive star evolution.
Similar to Detectcion of noble_gas_molecular_ion_arh_in_the_crab_nebula (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.
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.
The solar dynamo begins near the surfaceSérgio Sacani
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.
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.
Unlock the Future of Search with MongoDB Atlas_ Vector Search Unleashed.pdfMalak Abu Hammad
Discover how MongoDB Atlas and vector search technology can revolutionize your application's search capabilities. This comprehensive presentation covers:
* What is Vector Search?
* Importance and benefits of vector search
* Practical use cases across various industries
* Step-by-step implementation guide
* Live demos with code snippets
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Detectcion of noble_gas_molecular_ion_arh_in_the_crab_nebula
1. Detection of a Noble Gas Molecular Ion, 36ArH+, in the Crab Nebula
M. J. Barlow et al.
Science 342, 1343 (2013);
DOI: 10.1126/science.1243582
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2. REPORTS
Detection of a Noble Gas Molecular
Ion, 36ArH+, in the Crab Nebula
M. J. Barlow,1* B. M. Swinyard,1,2 P. J. Owen,1 J. Cernicharo,3 H. L. Gomez,4 R. J. Ivison,5
O. Krause,6 T. L. Lim,2 M. Matsuura,1 S. Miller,1 G. Olofsson,7 E. T. Polehampton2,8
Noble gas molecules have not hitherto been detected in space. From spectra obtained with
the Herschel Space Observatory, we report the detection of emission in the 617.5- and
1234.6-gigahertz J = 1-0 and 2-1 rotational lines of 36ArH+ at several positions in the Crab
Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced
ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis
in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the
product of such a supernova event, confirms this expectation. The likely excitation mechanism
for the observed 36ArH+ emission lines is electron collisions in partially ionized regions with
electron densities of a few hundred per centimeter cubed.
oble gas compounds have not yet been
found in space, despite some examples,
such as ionized hydrides, being relatively
stable (1). Astronomical searches for the nearinfrared and far-infrared lines of HeH+, whose
dissociation energy is 1.8 eV (2), have not been
successful (3, 4). The Crab Nebula is the product
of the supernova of 1054 AD and is thought to
have originated from the core-collapse explosion
of a star 8 to 16 times as massive as the Sun (5).
We have obtained far-infrared–to–submillimeter
spectra of the Crab Nebula using the Herschel
Space Observatory (6). We report here the detection of emission lines from the ionized hydride of
argon, an element predicted to form by explosive
nucleosynthesis in core-collapse supernovae (7).
The Crab Nebula was observed with the Fourier
Transform Spectrometer (FTS) of the Spectral
and Photometric Imaging Receiver (SPIRE) (8, 9)
on operational day 466 of the Herschel mission, as
part of the Mass-loss of Evolved Stars (MESS)
Guaranteed Time Key Project (10). The 19 SPIRE
Long Wavelength (SLW) detectors, each with a
beamwidth of ∼37 arc sec, covered the 447- to
989-GHz frequency range (303 to 671 mm), while
35 SPIRE Short Wavelength (SSW) detectors,
each with a beamwidth of ∼18 arc sec, covered
the 959- to 1544-GHz frequency range (194 to
N
1
Department of Physics and Astronomy, University College
London, Gower Street, London WC1E 6BT, UK. 2Space Science
and Technology Department, Rutherford Appleton Laboratory,
Didcot OX11 0QX, UK. 3Laboratory of Molecular Astrophysics,
Department of Astrophysics, Centro de Astrobiologia, Instituto
Nacional de Tecnicas Aeroespaciales–Consejo Superior de
Investigaciones Cientificas, Ctra de Ajalvir, km 4, 28850 Torrejón
de Ardoz, Madrid, Spain. 4School of Physics and Astronomy,
Cardiff University, The Parade, Cardiff CF24 3AA, UK. 5UK Astronomy Technology Centre, Royal Observatory Edinburgh,
Blackford Hill, Edinburgh EH9 3HJ, UK. 6Max-Planck-Institut
für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany.
7
Department of Astronomy, Stockholm University, AlbaNova
University Center, Roslagstulsbacken 21, 10691 Stockholm,
Sweden. 8Institute for Space Imaging Science, Department of
Physics and Astronomy, University of Lethbridge, Lethbridge,
Alberta T1K 3M4, Canada.
*Corresponding author. E-mail: mjb@star.ucl.ac.uk
313 mm) (Fig. 1). The full width at half maximum spectral resolution was 1.44 GHz at all frequencies, corresponding to a resolving power of
690 in the middle of the frequency range. The
observation consisted of 48 FTS scans, for a total
on-source exposure time of 3197 s. The data were
processed using the extended source calibration
in version 11 of the Herschel Interactive Processing Environment (11). The J = 2-1, F = 5/2-3/2
line of OH+ at 971.8038 GHz (12), which falls
in the SLW and SSW spectral overlap region, is
present in emission in many of the spectra (Fig. 2).
This line has been observed from a range of astrophysical environments by the Herschel Space
Observatory, both in absorption (13) and emission (14, 15). In addition, two unidentified
emission lines were found to be present in
some of the Crab spectra, one in the SLW range
at ∼618 GHz and the other in the SSW range at
∼1235 GHz.
The knots and filaments of the Crab Nebula
are known to exhibit expansion velocities ranging between 700 and 1800 km s−1 (16); in different detectors we measured radial velocities for
the OH+ 971.8038 GHz line that ranged between
–603 and +1037 km s−1. Several spectra showed
multiple OH+ velocity components, some blended,
but in most spectra the OH+ velocity components
were unresolved, exhibiting very different radial
velocities from detector to detector, consistent
with an origin from differing knots or filaments
in the nebula, each with its own discrete velocity. Because OH+ was the only identified species
in the spectra initially, we used the measured radial
velocities of the 971.8038 GHz OH+ line, whose
centroid frequency could typically be measured
to an accuracy of T(25 to 40) km s−1, as a reference to correct to a “rest” frequency the observed frequencies of the 618- or 1235-GHz line
falling in the same spectrum. There were four
SLW spectra, those from detectors B3, C3, D3
and D4, in which the OH+ line and the 618-GHz
line were both present, with emission line surface
brightnesses exceeding 2 × 10−10 W m−2 sr−1.
These four spectra yielded a mean “rest” frequency for the 618-GHz line of 617.554 T 0.209 GHz.
The 1235-GHz line was detected in five SSW
spectra (A2, B1, B2, B3, and D4), but only in
Fig. 1. A broadband Herschel–Photodetector Array Camera and Spectrometer image mapping
the 70-mm dust emission from the Crab Nebula. North is up and east is to the left. The positions on
the nebula of the 19 SLW and 35 SSW detectors of the SPIRE FTS are marked with circles whose angular
diameters of 37 and 18 arc sec correspond to the SLW and SSW beam sizes. The positions of detectors in
whose spectra the J = 1-0 or 2-1 rotational lines of 36ArH+ were detected are marked with crosses.
www.sciencemag.org
SCIENCE
VOL 342
13 DECEMBER 2013
1343
3. REPORTS
Fig. 2. SPIRE FTS spectra of the Crab Nebula,
+
36ArH +
OH
plotting surface bright−2
−1 −1
J=2-1
J=1-0
ness (in W m Hz sr )
F= 5/2 - 3/2
against frequency (in
GHz). Several emission
lines are superposed on
a continuum attributed
to thermal dust emission
(32). Upper plot: the spectrum from the SLW D4
detector, whose position
on the nebula is marked
in Fig. 1. Emission line velocity components attributed to the J = 2-1, F =
36ArH +
OH +
5/2-3/2 971.8038 GHz
J=2-1
J=2-1
+
rotational line of OH and
F= 5/2 - 3/2
the J = 1-0 617.525 GHz
rotational line of 36ArH+
are visible. Lower plot:
the SSW B1 spectrum. In
addition to OH+ 971.8038
GHz velocity components,
emission in the J = 2-1
1234.603 GHz line of 36ArH+ is visible. The radial velocities and surface brightnesses of the 36ArH+ emission lines that are present in the spectra obtained
from these and other FTS detectors are listed in Table 1.
the B1 (Fig. 2) and B3 spectra were both it and
the 971.8038 GHz OH+ line present with a single unresolved component. The J = 1-1, F =
1/2-1/2 line of OH+ at 1032.998 GHz was also
detected in emission in the SSW B1 spectrum,
enabling a third estimate of the rest frequency of
the 1235-GHz line. The mean frequency derived
from these three estimates was 1234.786 T
0.643 GHz.
The ratio of the derived rest frequencies of
1234.786 T 0.643 GHz and 617.554 T 0.209 GHz
is 1.9995 T 0.0012, which suggests that the lines
correspond to the 2-1 and 1-0 rotational transitions of a simple diatomic molecule (we can rule
out their being 4-3 and 2-1 transitions, with a frequency ratio of 4:2, because of the lack of a corresponding 3-2 transition at ∼926 GHz). A search
using the Cologne Database for Molecular Spectroscopy (12) and the madex code (17) found
the only candidate to be 36ArH+, whose 1-0 and
2-1 rotational transitions lie at 617.52523 T
0.00015 GHz and 1234.60275 T 0.00030 GHz,
respectively, agreeing with the derived frequencies
for the Crab Nebula lines within the uncertainties.
The 1-0 and 2-1 rotational transitions of 40ArH+ are
at 615.85813 T 0.00005 GHz and 1231.27100 T
0.00009 GHz, while the corresponding transitions of 38ArH+ are at 616.64871 T 0.00004 GHz
and 1232.85100 T 0.00004 GHz, ruling out these
two isotopic variants as identifications. Argon is
the third most abundant species in Earth’s atmosphere, 0.93% by number, with 40Ar/38Ar/36Ar
isotopic ratios of 1584/1.00/5.30 (18). However,
40
Ar in Earth’s atmosphere is a product of the
decay, mainly in rocks, of 40K, whose half-life is
1.25 × 109 years. For the solar wind, the 40Ar/38Ar/
36
Ar isotopic ratios have been measured to be
0.00/1.00/5.50 (19). 36Ar is expected to be the
1344
dominant isotope of argon in stars, being an explosive nucleosynthesis product of the a-particle
capture chain that takes place in massive-star corecollapse supernovae (7). Regions of enhanced
emission from optical forbidden lines of ionized
argon have previously been mapped in the Crab
Nebula (20–22), almost certainly corresponding to enriched argon abundances. Strongly enhanced infrared forbidden lines of Ar+ and Ar2+
have been detected from the southern filament
(22) where we find 36ArH+ line emission to be
strongest (SSW detector B1; Fig. 1 and Table 1).
The enhanced lines of ionized argon and 36ArH+
strongly indicate the presence there of pockets
of 36Ar produced by explosive nucleosynthesis
during the supernova event.
The 38Ar isotope of argon is also predicted to
be synthesized in core-collapse supernova events
(7). We used Crab Nebula SPIRE-FTS spectra in
which the 36ArH+ velocity components are strong
and narrow to put limits on the isotopic ratios of
40
Ar and 38Ar relative to 36Ar in the emitting regions. Because the frequency separation between
the isotopic variants of ArH+ is a factor of 2 larger
for the J = 2-1 lines than for the 1-0 lines, whereas the SPIRE-FTS frequency resolution is constant,
the 2-1 lines are better suited for placing limits on
the isotopic ratios of argon. Relative to the 36ArH+
2-1 line, the separation of the 40ArH+ 2-1 line is
–3.33175 GHz, while that of the 38ArH+ 2-1 line
is –1.75175 GHz. To estimate upper limits to the
abundances of these species, we added synthetic
lines to the spectra having the appropriate frequency offset and the same line width as the 36ArH+
2-1 line, changing the strength of the synthetic
lines until the signal-to-noise ratio estimated by
the line-fitting routine reached 3s. The SSW B1
(Fig. 2) and SSW B3 spectra both yielded 3s
13 DECEMBER 2013
VOL 342
SCIENCE
lower limits to the abundance ratio of 36ArH+/
ArH+ of >2, along with 36ArH+/ 40ArH+ lower
limits of >5 and >4, respectively.
ArH+ is a stable molecular ion [dissociation
energy D0 = 3.9 T 0.1 eV (1)] that has been studied
extensively in the laboratory. The Crab Nebula
consists predominantly of ionized gas, photoionized by synchrotron radiation from the pulsar
wind nebula (5, 16). It also contains many H2emitting neutral clumps (23, 24). Transition zones
between fully ionized and molecular gas will exist,
where ArH+ can be formed by the exothermic reaction Ar+ + H2 → ArH+ + H, releasing 1.49 eV
(25). If the elemental species created by the supernova explosion were still largely unmixed in the
remnant, then it is possible that ArH+ molecules
would be found only at interfaces between H-rich
gas and Ar-rich gas where mixing has occurred.
Four of the seven FTS SSW detectors in whose
spectra J = 2-1 36ArH+ emission was detected
(SSW B1, B2, A1, and A2) are situated on a bright
filament south of the center of the nebula (Fig. 1),
as is the SLW D4 detector in which the strongest
J = 1-0 emission was detected. A cluster of seven
near-infrared H2-emitting knots, with a wide range
of radial velocities, is coincident with the same
bright filament (24). Detectors SLW C3 and SSW
D4 also show 36ArH+ emission and are coincident with an H2-emitting knot. The lack of ArH+
emission in the northwest quadrant of the nebula
is mirrored by a relative lack of H2 emission knots
in that region. However, there are many H2 knots
in the northeast quadrant, whereas ArH+ emission is only detected there in two FTS detectors
(SLW E1 and E2).
The reaction rate for the formation of ArH+
via Ar+ + H2 → ArH+ + H is 8.9 × 10−10 cm3 s−1
at 300 K (25). Reaction rates are known for the
38
www.sciencemag.org
4. REPORTS
Table 1. SPIRE-FTS radial velocity and line surface brightness measurements for the J = 1-0
and 2-1 rotational lines of 36ArH+ from the Crab Nebula.
J = 1-0 617.525 GHz
SLW detector
Radial
velocity
(km s−1)
T
T
T
T
T
T
B3
C3
C4
D3
D3
D4
+317
+933
–58
+826
–709
+101
67
33
50
32
42
27
E1
E2
+278 T 46
–594 T 37
J = 2-1 1234.603 GHz
Surface
brightness
(10−10 W m−2 sr−1)
2.23
4.63
8.65
3.13
2.30
9.89
T
T
T
T
T
T
0.41
0.40
0.55
0.34
0.34
0.52
SSW
detector
Radial velocity
(km s−1)
Surface
brightness
(10−10 W m−2 sr−1)
C5
D4
B3
–1354 T 26
+743 T 26
–101 T 20
8.2 T 1.2
11.7 T 1.6
17.5 T 1.4
A1
B2
B1
A2
5.69 T 0.62
4.25 T 0.46
ArH+ destruction reaction with H2 [to yield Ar +
H3+, with a reaction rate of 6.3 × 10−10 cm3 s−1
at 300 K (26)] and for its dissociative recombination with electrons [ArH+ + e− → Ar + H*,
with a rate of ≤5 × 10−10 cm3 s−1 at low electron
energies (27)]. However, because the Crab Nebula
is photoionized by its pulsar wind nebula (5, 16),
photodissociation could be the main ArH+ destruction mechanism.
The main excitation mechanism for the observed ArH+ emission lines is likely to be collisions with either electrons or H2 molecules, but
rate calculations or measurements do not yet exist.
The J = 1 and 2 levels of 36ArH+ are situated 29.6
and 88.9 K above the ground state, respectively,
which is negligible compared to the electron temperatures of 7500 to 15,000 K measured for the
ionized gas in the Crab Nebula (5), or even compared to the H2 excitation temperatures of 2000
to 3000 K that have been measured (28). If the
electron or H2 densities in the transition zones
where ArH+ is hypothesized to be located should
exceed the “critical densities” of the emitting
levels (where the sum of the collisional excitation and deexcitation rates from a level exceed
the radiative decay rate from the level), then the
level populations will be in Boltzmann equilibrium. Using the known molecular parameters of
ArH+ (12, 17), the 2-1/1-0 line emission ratios
should then be on the order of 30, for excitation
temperatures appreciably exceeding 100 K. The
SSW D4 and SLW C3 detectors are centered on
the same bright knot (Fig. 1) and yield a 2-1/1-0
line surface brightness ratio of 2.5, while the
spectra from the approximately colocated SSW
B3 and SLW C4 detectors yield a line surface
brightness ratio of 2.0 (Table 1), well below the
ratio for Boltzmann equilibrium. The densities
of the collision partners in the emitting regions
must therefore be well below the corresponding
critical densities of the ArH+ rotational levels.
We used the MADEX code (17) with the molecular parameters of ArH+, together with SiH+ +
He collisional deexcitation rates (29) in place of
those of ArH+ + H2, and CH+ + e− collisional de-
–51
–572
+140
+61
T
T
T
T
52
25
34
28
13.9
10.8
38.4
10.1
T
T
T
T
2.0
1.7
1.6
1.4
excitation rates (30) in place of those for ArH+ + e−
(with upward rates calculated using detailed balance and the correct values of the energies for
the levels of ArH+) to estimate corresponding
H2 and electron critical densities of ∼108 and
∼104 cm−3, respectively. The observed 2-1/1-0
line ratios of 2.5 and 2.0 indicate H2 densities
of a few × 106 cm−3 or electron densities of a
few × 102 cm−3. The calculations take into account opacity effects, although the line center
optical depths are estimated to be appreciably
less than unity for line widths larger than 1 km s−1.
For H2 collisions at temperatures between 100
and 3000 K and densities of ∼106 cm−3, or electron collisions at temperatures of ∼3000 K and
densities of a few × 102 cm−3, we estimate 36ArH+
column densities of 1012 to 1013 cm−2.
Given that likely electron collisional excitation rates are ∼104 larger than those of H2 and
that the parent Ar+ ion must exist in a region
that is at least partially ionized, electron collisions are expected to dominate the excitation
of ArH+. A density of ∼104 cm−3 has been estimated for the Crab H2 knots (28), a factor of
100 below that required for H2 collisions to be
the excitation mechanism for the ArH+ lines.
This lends further support to electron collisions
in partially ionized transition regions being the
main ArH+ excitation mechanism.
Our detection of 36ArH+ in the Crab Nebula
suggests that an unidentified multicomponent
broad absorption feature seen between 617 and
618 GHz in a Herschel HIFI spectrum of Sgr
B2(M) (toward the center of our galaxy) (31)
can potentially be identified with ground-state
absorption in the J = 0-1 617.525 GHz line of
36
ArH+ along the interstellar sightline.
References and Notes
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2. S. G. Lias, J. F. Liebman, R. D. Levin, J. Phys. Chem. Ref.
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3. J. M. Moorhead, R. P. Lowe, W. H. Wehlau, J.-P. Maillard,
P. F. Bernath, Astrophys. J. 326, 899 (1988).
4. X.-W. Liu et al., Mon. Not. R. Astron. Soc. 290, L71–L75
(1997).
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23, 119–146 (1985).
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Acknowledgments: We thank the anonymous referees for
their constructive reports. We thank E. Bergin for drawing our
attention to the 2010 HEXOS Herschel HIFI spectrum of SgR B2
(M) that shows an unidentified broad absorption feature below
618 GHz. Herschel is a European Space Agency (ESA) space
observatory with science instruments provided by European-led
Principal Investigator consortia and with important participation
from NASA. SPIRE has been developed by a consortium of
institutes led by Cardiff University (UK) and including
University of Lethbridge (Canada); National Astronomical
Observatories, Chinese Academy of Sciences Commissariat á
l‘énergie atomique et aux énergies alternatives Laboratoire
d‘Astrophysique de Marseille (France); Istituto di fisica dello
Spazio Interplanetario University of Padua (Italy); Instituto de
Astrofísica de Canarias (Spain); Stockholm Observatory
(Sweden); Imperial College London, Rutherford Appleton
Laboratory, University College London–Mullard Space Science
Laboratory, United Kingdom Astronomy Technology Centre,
University of Sussex (UK); and California Institute of Technology,
Jet Propulson Laboratory, NASA Herschel Science Center,
University of Colorado (USA). This development has been
supported by national funding agencies: Canadian Space Agency
(Canada); NAOC (China); CEA, Centre national d‘études spatiales,
Centre national de la recherche scientifique (France); Agenzia
Spaziale Italiana (Italy); Ministerio de Economia (Spain);
Swedish National Space Board (Sweden); Science Technology
and Facilities Council and United Kingdom Space Agency (UK);
and NASA (USA). J.C. thanks MINECO for financial support
under projects AYA2009-07304, AYA2012-32032, and
Consolider program ASTROMOL CSD2009-00038.
22 July 2013; accepted 5 November 2013
10.1126/science.1243582
13 DECEMBER 2013
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