Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Gravitational waves from ejection of jet superluminal components and precession of accretion disk dynamically driven by bardeen petterson efect
1) The document discusses the potential detection of gravitational waves from the ejection of superluminal jet components and precession of accretion disks dynamically driven by the Bardeen-Petterson effect around spinning black holes.
2) It suggests that ejection of ultrarelativistic jet components may be associated with the precession of the accretion disk induced by the black hole's spin and fragmentation of the tilted disk due to the Bardeen-Petterson effect.
3) It computes the characteristic amplitude and frequency of gravitational wave bursts that could be produced during the early acceleration phase of launching superluminal jet components, finding they may be detectable by the gravitational wave observatory LISA.
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
This document summarizes the detection of a super-Earth planet orbiting the star GJ 832. Radial velocity data from three telescopes revealed a planet, GJ 832c, with an orbital period of 35.68 days and a minimum mass of 5.4 Earth masses. GJ 832c has a low eccentricity orbit of 0.18 near the inner edge of the star's habitable zone. However, given its large mass, the planet likely has a massive atmosphere that could render it uninhabitable. The GJ 832 system resembles a miniature version of our solar system, with an interior potentially rocky planet and a distant gas giant.
Misaligned Protoplanetary Disks in a Young Binary Star SystemGOASA
This document reports on observations of the protoplanetary disks around the young binary star system HK Tau using millimeter wavelength observations. The observations reveal that the disks around the two stars, HK Tau A and HK Tau B, are misaligned with each other by 60-68 degrees. This demonstrates that the disks formed misaligned from the binary orbital plane, providing evidence that interactions between misaligned disks and binary companions could influence the orbits of forming planets. It also shows that conditions conducive to producing misaligned planetary orbits exist early in the planet formation process.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
This document reports the first detections of Blue Straggler Stars (BSS) in the Milky Way bulge. Proper motions and variability measurements from Hubble Space Telescope observations were used to separate a clean bulge sample and identify BSS candidates. Of 42 candidate BSS identified, variability measurements indicate that at least 18 are genuine BSS, while contamination estimates suggest the true BSS population could be as high as 37 objects. This establishes for the first time that BSS exist as a population in the Milky Way bulge.
A surge of light at the birth of a supernovaSérgio Sacani
It is difficult to establish the properties of massive stars that explode
as supernovae1,2
. The electromagnetic emission during the first
minutes to hours after the emergence of the shock from the stellar
surface conveys important information about the final evolution
and structure of the exploding star3–6. However, the unpredictable
nature of supernova events hinders the detection of this brief initial
phase7–9. Here we report the serendipitous discovery of a newly
born, normal type IIb supernova (SN 2016gkg)10, which reveals a
rapid brightening at optical wavelengths of about 40 magnitudes
per day. The very frequent sampling of the observations allowed
us to study in detail the outermost structure of the progenitor of
the supernova and the physics of the emergence of the shock. We
develop hydrodynamical models of the explosion that naturally
account for the complete evolution of the supernova over distinct
phases regulated by different physical processes. This result
suggests that it is appropriate to decouple the treatment of the
shock propagation from the unknown mechanism that triggers
the explosion.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
This document summarizes the detection of a super-Earth planet orbiting the star GJ 832. Radial velocity data from three telescopes revealed a planet, GJ 832c, with an orbital period of 35.68 days and a minimum mass of 5.4 Earth masses. GJ 832c has a low eccentricity orbit of 0.18 near the inner edge of the star's habitable zone. However, given its large mass, the planet likely has a massive atmosphere that could render it uninhabitable. The GJ 832 system resembles a miniature version of our solar system, with an interior potentially rocky planet and a distant gas giant.
Misaligned Protoplanetary Disks in a Young Binary Star SystemGOASA
This document reports on observations of the protoplanetary disks around the young binary star system HK Tau using millimeter wavelength observations. The observations reveal that the disks around the two stars, HK Tau A and HK Tau B, are misaligned with each other by 60-68 degrees. This demonstrates that the disks formed misaligned from the binary orbital plane, providing evidence that interactions between misaligned disks and binary companions could influence the orbits of forming planets. It also shows that conditions conducive to producing misaligned planetary orbits exist early in the planet formation process.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
This document reports the first detections of Blue Straggler Stars (BSS) in the Milky Way bulge. Proper motions and variability measurements from Hubble Space Telescope observations were used to separate a clean bulge sample and identify BSS candidates. Of 42 candidate BSS identified, variability measurements indicate that at least 18 are genuine BSS, while contamination estimates suggest the true BSS population could be as high as 37 objects. This establishes for the first time that BSS exist as a population in the Milky Way bulge.
A surge of light at the birth of a supernovaSérgio Sacani
It is difficult to establish the properties of massive stars that explode
as supernovae1,2
. The electromagnetic emission during the first
minutes to hours after the emergence of the shock from the stellar
surface conveys important information about the final evolution
and structure of the exploding star3–6. However, the unpredictable
nature of supernova events hinders the detection of this brief initial
phase7–9. Here we report the serendipitous discovery of a newly
born, normal type IIb supernova (SN 2016gkg)10, which reveals a
rapid brightening at optical wavelengths of about 40 magnitudes
per day. The very frequent sampling of the observations allowed
us to study in detail the outermost structure of the progenitor of
the supernova and the physics of the emergence of the shock. We
develop hydrodynamical models of the explosion that naturally
account for the complete evolution of the supernova over distinct
phases regulated by different physical processes. This result
suggests that it is appropriate to decouple the treatment of the
shock propagation from the unknown mechanism that triggers
the explosion.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
A estrela KIC 8462852 voltou a ser comentada na mídia astronômica essa semana, e vamos entender porque. Mas antes uma pequena recordação.
Provavelmente, você já ouviu falar da estrela KIC 8462852, que recebeu o nome carinhoso de Estrela de Tabby, em homenagem a Tabetha Boyajian que liderou a equipe que descobriu o seu estranho comportamento. Essa foi a estrela que chamou muito a atenção da imprensa no final do último ano. Os astrônomos utilizaram observações feitas com o Kepler e mediram as variações no brilho da estrela. Algumas dessas variações eram significativas, com uma queda de brilho de cerca de 20%.
Isso é muito. Não poderia ser um planeta passando em frente a estrela, pois as quedas dos brilhos também não eram periódicas, e a quantidade de luz bloqueada era diferente a cada vez. Além disso, até um planeta do tamanho de Júpiter, bloqueia menos de 1% da luz da estrela.
No artigo original, Boyajian e sua equipe discutiu uma série de hipóteses e possíveis cenários que poderiam causar a queda de brilho, eliminando algumas delas e levantando outras. Entre as hipóteses, aquela que ganhou uma força foi a de uma família de cometas passando na frente da estrela, com alguns deles colidindo entre si e gerando uma nuvem espessa que poderia bloquear a luz da estrela.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
Chiotelis Ioannis, Theodoropoulou Maria, “Searching for Black Holes. Photometry in our Classrooms”, Hellenic Conference on Innovating STEM Education, 16-18 December 2016, Athens, Greece.
Initial characterization of interstellar comet 2I/BorisovSérgio Sacani
Interstellar comets penetrating through the Solar System had
been anticipated for decades1,2
. The discovery of asteroidallooking ‘Oumuamua3,4 was thus a huge surprise and a puzzle.
Furthermore, the physical properties of the ‘first scout’ turned
out to be impossible to reconcile with Solar System objects4–6,
challenging our view of interstellar minor bodies7,8. Here, we
report the identification and early characterization of a new
interstellar object, which has an evidently cometary appearance. The body was discovered by Gennady Borisov on 30
August 2019 ut and subsequently identified as hyperbolic by
our data mining code in publicly available astrometric data.
The initial orbital solution implies a very high hyperbolic excess
speed of ~32 km s−1
, consistent with ‘Oumuamua9 and theoretical predictions2,7
. Images taken on 10 and 13 September
2019 ut with the William Herschel Telescope and Gemini
North Telescope show an extended coma and a faint, broad
tail. We measure a slightly reddish colour with a g′–r′ colour
index of 0.66 ± 0.01 mag, compatible with Solar System comets. The observed morphology is also unremarkable and best
explained by dust with a power-law size-distribution index
of –3.7 ± 1.8 and a low ejection speed (44 ± 14 m s−1
for β= 1
particles, where β is the ratio of the solar gravitational attraction to the solar radiation pressure). The nucleus is probably
~1 km in radius, again a common value among Solar System
comets, and has a negligible chance of experiencing rotational
disruption. Based on these early characteristics, and putting
its hyperbolic orbit aside, 2I/Borisov appears indistinguishable from the native Solar System comets.
No global pluto_like_atmosphere_on_dwarf_planet_makemake_from_a_stellar_occul...Sérgio Sacani
1. A stellar occultation event was observed involving the dwarf planet Makemake on April 23, 2011 using multiple telescopes.
2. Analysis of the light curves from the event showed abrupt disappearances and reappearances of the star, indicating Makemake has no global atmosphere at an upper limit of 4-12 nanobar surface pressure.
3. The occultation data was used to determine Makemake has dimensions of 1,430±9 km by 1,502±45 km, implying a high geometric albedo of 0.77±0.03. This rules out a low density and suggests Makemake is in hydrostatic equilibrium as an oblate spheroid.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Shaping the glowing_eye_planetary_nebula_ngc6751Sérgio Sacani
This document presents a comprehensive study of the planetary nebula NGC 6751 using spectroscopic observations and imaging. It finds:
1) NGC 6751 has a thick equatorial ring fragmented into knots enclosing a central bubble, surrounded by faint envelope and bipolar lobes with filaments.
2) Kinematic data identify distinct velocities for different components: the outer halo at -15 km/s, inner halo at -31 km/s, and bipolar lobes at ±30 km/s.
3) A 3D morpho-kinematic model is constructed using the SHAPE code that closely matches the observed images and spectra, providing insight into the nebula's complex structure.
Kepler-1647b is the largest and longest-period Kepler transiting circumbinary planet discovered to date. It orbits an eclipsing binary star system with an orbital period of approximately 1100 days, making it one of the longest-period transiting planets known. The planet is around 1.06 times the size of Jupiter and perturbes the times of the stellar eclipses, allowing its mass to be measured at 1.52 times that of Jupiter. Despite its long orbital period compared to Earth, the planet resides in the habitable zone of the binary star system throughout its orbit. The discovery of this unusual planetary system provides insights into theories of planet formation and dynamics in multiple star systems.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
Mapping the complex_kinematics_of_l_lobjects_in_the_orion_nebulaSérgio Sacani
This document presents a study of the kinematics of two LL Orionis-type objects (LL objects) in the Orion nebula, LL 1 and LL 2, and their associated Herbig-Haro jets HH 888 and HH 505. The authors combine long-slit spectroscopic observations of the objects with proper motion measurements to construct 3D velocity maps. The maps reveal:
1) Low velocities (10-20 km/s) in the stellar bowshocks of LL 1 and LL 2, with LL 1 showing symmetric motions and LL 2 showing asymmetric motions following nebula gradients.
2) Jet knot velocities over 200 km/s near the stars declining to under 100 km/s farther out in HH 8
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
This document summarizes the discovery of a fourth planet orbiting the red dwarf star GJ 581. The planet, called GJ 581e, has a minimum mass of 1.9 Earth masses and orbits with a period of 3.15 days, making it the innermost planet in the system. Updated radial velocity measurements also allowed the researchers to correct the orbital period of the outermost planet GJ 581d, determining it to be 66.8 days rather than the previously reported 83 days. This revised period places GJ 581d within the star's habitable zone. The researchers conclude the GJ 581 system has 4 planets, with the detection of GJ 581e being the lowest mass exoplanet
50 Years of the Astronomy Centre at the University of SussexPeter Coles
This summarizes about 50 research papers and other notable events, approximately one for each year of existence of the Astronomy Centre at the University of Sussex (1966-2016). Shown at a special event on 15th October 2016. to mark the 50th Anniversary
Hd140283 a star_in_the_solar_neighborhood_that_formed_shortly_after_the_big_bangSérgio Sacani
This document summarizes a study that measured the parallax of the star HD 140283 using the Hubble Space Telescope's Fine Guidance Sensors. The study found a parallax of 17.15 ± 0.14 mas, improving on the previous measurement from Hipparcos. Using modern stellar evolution models, the authors estimate an age for HD 140283 of 14.46 ± 0.31 Gyr based on its precise distance, making it one of the oldest stars known. While its age is consistent with the age of the Universe, uncertainties in the star's composition increase the total age uncertainty to about ±0.8 Gyr. HD 140283 likely formed shortly after the Big Bang.
Direct imaging of_a_cold_jovian_exoplanet_in_orbit_around_the_sun_like_star_g...Sérgio Sacani
Direct imaging observations using Subaru Telescope detected an exoplanet, GJ 504 b, orbiting the Sun-like star GJ 504. GJ 504 b has an estimated mass of 4+4.5−1.0 Jupiter masses and orbits at a projected separation of 43.5 AU from its host star. At an age of 160+350−60 Myr for the system, GJ 504 b's mass estimate is relatively insensitive to uncertainties in giant planet formation models. GJ 504 b is cooler (510+30−20 K) and has a bluer color than previously imaged exoplanets, suggesting a clearer atmosphere amenable to spectroscopic study. Its discovery provides an opportunity to gain new insights into the origins and
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
Apartes de la Conferencia de la SJG 14 y 21 de Enero de 2012:Gravitational wa...SOCIEDAD JULIO GARAVITO
This document discusses gravitational waves that may be produced by the ejection of superluminal jet components from active galactic nuclei, microquasars, and other astrophysical systems. It proposes that ejection may be associated with the precession of the accretion disk, induced by the black hole's spin, and fragmentation of the tilted disk due to the Bardeen-Petterson effect. As the disk fragments at the Bardeen-Petterson transition radius, a suspended accretion state can develop, distorting the inner disk and generating gravitational waves from turbulent flow. Ejection of blobs at the transition radius may also produce gravitational wave bursts during early acceleration. The document estimates characteristic amplitudes and frequencies of such signals, finding potential detectability
Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Alternative...SOCIEDAD JULIO GARAVITO
1. The document discusses nonlinear electrodynamics (NLED) as an alternative field theory to explain the Pioneer anomaly.
2. NLED predicts that photons travel along an effective metric rather than the background geometry, which can result in photon acceleration and a shift in photon frequency.
3. Several Lagrangian formulations of NLED are reviewed, including the Heisenberg-Euler approach, which describes photon dynamics and predicts that electromagnetic fields affect the propagation of photons in vacuum.
Artigo descreve a descoberta do exoplaneta HATS-6b, um exoplaneta parecido com Saturno, porém pesado como Júpiter ao redor de uma estrela anã-M, o tipo de estrela mais abundante na nossa galáxia.
A estrela KIC 8462852 voltou a ser comentada na mídia astronômica essa semana, e vamos entender porque. Mas antes uma pequena recordação.
Provavelmente, você já ouviu falar da estrela KIC 8462852, que recebeu o nome carinhoso de Estrela de Tabby, em homenagem a Tabetha Boyajian que liderou a equipe que descobriu o seu estranho comportamento. Essa foi a estrela que chamou muito a atenção da imprensa no final do último ano. Os astrônomos utilizaram observações feitas com o Kepler e mediram as variações no brilho da estrela. Algumas dessas variações eram significativas, com uma queda de brilho de cerca de 20%.
Isso é muito. Não poderia ser um planeta passando em frente a estrela, pois as quedas dos brilhos também não eram periódicas, e a quantidade de luz bloqueada era diferente a cada vez. Além disso, até um planeta do tamanho de Júpiter, bloqueia menos de 1% da luz da estrela.
No artigo original, Boyajian e sua equipe discutiu uma série de hipóteses e possíveis cenários que poderiam causar a queda de brilho, eliminando algumas delas e levantando outras. Entre as hipóteses, aquela que ganhou uma força foi a de uma família de cometas passando na frente da estrela, com alguns deles colidindo entre si e gerando uma nuvem espessa que poderia bloquear a luz da estrela.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
Chiotelis Ioannis, Theodoropoulou Maria, “Searching for Black Holes. Photometry in our Classrooms”, Hellenic Conference on Innovating STEM Education, 16-18 December 2016, Athens, Greece.
Initial characterization of interstellar comet 2I/BorisovSérgio Sacani
Interstellar comets penetrating through the Solar System had
been anticipated for decades1,2
. The discovery of asteroidallooking ‘Oumuamua3,4 was thus a huge surprise and a puzzle.
Furthermore, the physical properties of the ‘first scout’ turned
out to be impossible to reconcile with Solar System objects4–6,
challenging our view of interstellar minor bodies7,8. Here, we
report the identification and early characterization of a new
interstellar object, which has an evidently cometary appearance. The body was discovered by Gennady Borisov on 30
August 2019 ut and subsequently identified as hyperbolic by
our data mining code in publicly available astrometric data.
The initial orbital solution implies a very high hyperbolic excess
speed of ~32 km s−1
, consistent with ‘Oumuamua9 and theoretical predictions2,7
. Images taken on 10 and 13 September
2019 ut with the William Herschel Telescope and Gemini
North Telescope show an extended coma and a faint, broad
tail. We measure a slightly reddish colour with a g′–r′ colour
index of 0.66 ± 0.01 mag, compatible with Solar System comets. The observed morphology is also unremarkable and best
explained by dust with a power-law size-distribution index
of –3.7 ± 1.8 and a low ejection speed (44 ± 14 m s−1
for β= 1
particles, where β is the ratio of the solar gravitational attraction to the solar radiation pressure). The nucleus is probably
~1 km in radius, again a common value among Solar System
comets, and has a negligible chance of experiencing rotational
disruption. Based on these early characteristics, and putting
its hyperbolic orbit aside, 2I/Borisov appears indistinguishable from the native Solar System comets.
No global pluto_like_atmosphere_on_dwarf_planet_makemake_from_a_stellar_occul...Sérgio Sacani
1. A stellar occultation event was observed involving the dwarf planet Makemake on April 23, 2011 using multiple telescopes.
2. Analysis of the light curves from the event showed abrupt disappearances and reappearances of the star, indicating Makemake has no global atmosphere at an upper limit of 4-12 nanobar surface pressure.
3. The occultation data was used to determine Makemake has dimensions of 1,430±9 km by 1,502±45 km, implying a high geometric albedo of 0.77±0.03. This rules out a low density and suggests Makemake is in hydrostatic equilibrium as an oblate spheroid.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Shaping the glowing_eye_planetary_nebula_ngc6751Sérgio Sacani
This document presents a comprehensive study of the planetary nebula NGC 6751 using spectroscopic observations and imaging. It finds:
1) NGC 6751 has a thick equatorial ring fragmented into knots enclosing a central bubble, surrounded by faint envelope and bipolar lobes with filaments.
2) Kinematic data identify distinct velocities for different components: the outer halo at -15 km/s, inner halo at -31 km/s, and bipolar lobes at ±30 km/s.
3) A 3D morpho-kinematic model is constructed using the SHAPE code that closely matches the observed images and spectra, providing insight into the nebula's complex structure.
Kepler-1647b is the largest and longest-period Kepler transiting circumbinary planet discovered to date. It orbits an eclipsing binary star system with an orbital period of approximately 1100 days, making it one of the longest-period transiting planets known. The planet is around 1.06 times the size of Jupiter and perturbes the times of the stellar eclipses, allowing its mass to be measured at 1.52 times that of Jupiter. Despite its long orbital period compared to Earth, the planet resides in the habitable zone of the binary star system throughout its orbit. The discovery of this unusual planetary system provides insights into theories of planet formation and dynamics in multiple star systems.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
Mapping the complex_kinematics_of_l_lobjects_in_the_orion_nebulaSérgio Sacani
This document presents a study of the kinematics of two LL Orionis-type objects (LL objects) in the Orion nebula, LL 1 and LL 2, and their associated Herbig-Haro jets HH 888 and HH 505. The authors combine long-slit spectroscopic observations of the objects with proper motion measurements to construct 3D velocity maps. The maps reveal:
1) Low velocities (10-20 km/s) in the stellar bowshocks of LL 1 and LL 2, with LL 1 showing symmetric motions and LL 2 showing asymmetric motions following nebula gradients.
2) Jet knot velocities over 200 km/s near the stars declining to under 100 km/s farther out in HH 8
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
This document summarizes the discovery of a fourth planet orbiting the red dwarf star GJ 581. The planet, called GJ 581e, has a minimum mass of 1.9 Earth masses and orbits with a period of 3.15 days, making it the innermost planet in the system. Updated radial velocity measurements also allowed the researchers to correct the orbital period of the outermost planet GJ 581d, determining it to be 66.8 days rather than the previously reported 83 days. This revised period places GJ 581d within the star's habitable zone. The researchers conclude the GJ 581 system has 4 planets, with the detection of GJ 581e being the lowest mass exoplanet
50 Years of the Astronomy Centre at the University of SussexPeter Coles
This summarizes about 50 research papers and other notable events, approximately one for each year of existence of the Astronomy Centre at the University of Sussex (1966-2016). Shown at a special event on 15th October 2016. to mark the 50th Anniversary
Hd140283 a star_in_the_solar_neighborhood_that_formed_shortly_after_the_big_bangSérgio Sacani
This document summarizes a study that measured the parallax of the star HD 140283 using the Hubble Space Telescope's Fine Guidance Sensors. The study found a parallax of 17.15 ± 0.14 mas, improving on the previous measurement from Hipparcos. Using modern stellar evolution models, the authors estimate an age for HD 140283 of 14.46 ± 0.31 Gyr based on its precise distance, making it one of the oldest stars known. While its age is consistent with the age of the Universe, uncertainties in the star's composition increase the total age uncertainty to about ±0.8 Gyr. HD 140283 likely formed shortly after the Big Bang.
Direct imaging of_a_cold_jovian_exoplanet_in_orbit_around_the_sun_like_star_g...Sérgio Sacani
Direct imaging observations using Subaru Telescope detected an exoplanet, GJ 504 b, orbiting the Sun-like star GJ 504. GJ 504 b has an estimated mass of 4+4.5−1.0 Jupiter masses and orbits at a projected separation of 43.5 AU from its host star. At an age of 160+350−60 Myr for the system, GJ 504 b's mass estimate is relatively insensitive to uncertainties in giant planet formation models. GJ 504 b is cooler (510+30−20 K) and has a bluer color than previously imaged exoplanets, suggesting a clearer atmosphere amenable to spectroscopic study. Its discovery provides an opportunity to gain new insights into the origins and
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
Similar to Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Gravitational waves from ejection of jet superluminal components and precession of accretion disk dynamically driven by bardeen petterson efect
Apartes de la Conferencia de la SJG 14 y 21 de Enero de 2012:Gravitational wa...SOCIEDAD JULIO GARAVITO
This document discusses gravitational waves that may be produced by the ejection of superluminal jet components from active galactic nuclei, microquasars, and other astrophysical systems. It proposes that ejection may be associated with the precession of the accretion disk, induced by the black hole's spin, and fragmentation of the tilted disk due to the Bardeen-Petterson effect. As the disk fragments at the Bardeen-Petterson transition radius, a suspended accretion state can develop, distorting the inner disk and generating gravitational waves from turbulent flow. Ejection of blobs at the transition radius may also produce gravitational wave bursts during early acceleration. The document estimates characteristic amplitudes and frequencies of such signals, finding potential detectability
Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Alternative...SOCIEDAD JULIO GARAVITO
1. The document discusses nonlinear electrodynamics (NLED) as an alternative field theory to explain the Pioneer anomaly.
2. NLED predicts that photons travel along an effective metric rather than the background geometry, which can result in photon acceleration and a shift in photon frequency.
3. Several Lagrangian formulations of NLED are reviewed, including the Heisenberg-Euler approach, which describes photon dynamics and predicts that electromagnetic fields affect the propagation of photons in vacuum.
Artigo descreve a descoberta do exoplaneta HATS-6b, um exoplaneta parecido com Saturno, porém pesado como Júpiter ao redor de uma estrela anã-M, o tipo de estrela mais abundante na nossa galáxia.
Interchange reconnection as the source of the fast solar wind within coronal ...Sérgio Sacani
1) Recent measurements from Parker Solar Probe showed that the fast solar wind emerging from coronal holes is organized into 'microstreams' with an angular scale similar to underlying supergranulation cells associated with horizontal flows in the photosphere.
2) During a solar encounter where Parker Solar Probe came within 12.3 solar radii of the photosphere, plasma, energetic ion, and magnetic field measurements showed discrete microstreams structured at scales of supergranulation, with associated switchbacks of the radial magnetic field.
3) Correlation of the microstream and switchback structure with the spatial periodicity of the surface magnetic field suggests that interchange reconnection between open and closed magnetic fields in the low corona is driving the bursts observed by
This research news article discusses two studies that propose different models to explain an unusual gamma-ray burst (GRB) called the "Christmas burst" that occurred on Christmas Day in 2010.
One study suggests the GRB originated from a tightly bound binary system of a neutron star and supergiant helium star that merged, producing a jet within a common gas envelope. The other study proposes that a minor body like an asteroid or comet was tidally disrupted after passing close to a neutron star, producing debris that formed a disk and caused multiple emission peaks.
While both models can explain aspects of the complex data from the unusual GRB, the article notes that at least one model must be incorrect as the definitive proof
The formation of_a_quadruple_star_system_with_wide_separationSérgio Sacani
Artigo da Nature que reporta a observação feita da formação de um sistema quadruplo de estrelas. Pela primeira vez, os estágios iniciais de formação desse tipo de sistema é observado.
Serendipitous discovery of an extended xray jet without a radio counterpart i...Sérgio Sacani
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of
an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous
radio source at redshift z = 2:5. This is one of only few examples of high-redshift X-ray jets known
to date. It has a clear extension of about 1200, corresponding to a projected length of 100 kpc, with
a possible hot spot located 3500 from the quasar. The archival high resolution VLA maps surprisingly
reveal no extended jet emission, except for one knot about 1:400 from the quasar. The high X-ray to
radio luminosity ratio for this source appears consistent with the / (1 + z)4 amplication expected
from the inverse Compton radiative model. This serendipitous discovery may signal the existence
of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a
selection bias which must be accounted for when drawing any conclusions about the redshift evolution
of jet properties and indeed about the cosmological evolution of supermassive black holes and active
galactic nuclei in general.
A rock composition_for_earth_sized_exoplanetsSérgio Sacani
1) Researchers measured the mass of Kepler-78b, an Earth-sized exoplanet orbiting its host star every 8.5 hours, to be 1.69 ± 0.41 M⊕ using Doppler spectroscopy of the star's radial velocity variations.
2) Given the planet's radius of 1.20 ± 0.09 R⊕, its mean density of 5.3 ± 1.8 g/cm3 is similar to Earth's, suggesting a rocky composition of iron and rock.
3) Kepler-78b is the smallest exoplanet yet characterized with both an accurate mass and radius measurement, extending measurements of planetary composition into the size range of Earth and Venus.
1) PSR J033711715 is a millisecond pulsar discovered to be in a hierarchical triple system with two white dwarf companions, making it the first known millisecond pulsar triple system.
2) Precise timing observations using multiple radio telescopes determined the masses of the pulsar (1.4378 solar masses), inner white dwarf companion (0.19751 solar masses), and outer white dwarf companion (0.4101 solar masses) to high precision.
3) The unexpectedly coplanar and nearly circular orbits of the system indicate an exotic evolutionary history and provide an opportunity to test theories of general relativity by studying the interactions between the bodies.
Evidence for an intermediate-mass black hole in the globular cluster NGC 6624Sérgio Sacani
This document summarizes evidence for an intermediate-mass black hole located at the center of the globular cluster NGC 6624. The authors present over 25 years of timing observations of the millisecond pulsar PSR B1820-30A, which is located very close to the cluster center. Modeling of the higher order rotational frequency derivatives reveals that the pulsar is likely in a high-eccentricity orbit around a massive companion with a mass greater than 7500 solar masses located at the cluster center, which would be an intermediate-mass black hole. Additional evidence from modeling the cluster gravitational potential and dynamics supports the presence of a central black hole with a minimum mass of around 60,000 solar masses. The observations of this
The document summarizes observations of two giant radio lobes emanating from the center of the Milky Way galaxy. The lobes extend about 60 degrees from the galactic center and correspond closely with previously observed gamma-ray "Fermi bubbles". The lobes contain three ridge-like substructures that curve towards the galactic west as they extend away from the center. Strong magnetic fields of up to 15 microgauss permeate the lobes. The observations indicate that the radio lobes originate from a biconical outflow driven by intense star formation in the galactic center, rather than activity from the supermassive black hole, and have transported a huge amount of magnetic energy into the galactic halo over at least the past 10 million years.
Giant magnetized outflows from the centre of the Milky WayCarlos Bella
The document summarizes observations of two giant radio lobes emanating from the center of the Milky Way galaxy. The lobes extend about 60 degrees from the galactic center and correspond closely to previously observed gamma-ray "Fermi bubbles". The lobes contain three ridge-like substructures that curve towards the galactic west as they extend away from the center. Strong magnetic fields of up to 15 microgauss permeate the lobes. The observations indicate that the radio lobes originate from a biconical outflow driven by intense star formation in the galactic center, rather than activity from the supermassive black hole, and have transported a huge amount of magnetic energy into the galactic halo over at least the past 10 million years. The ridges
This document summarizes the discovery of an Earth-mass planet orbiting the star Alpha Centauri B. The planet, with a minimum mass similar to Earth, has an orbital period of 3.236 days and is located about 0.04 astronomical units from the star. High-precision radial velocity measurements from the HARPS spectrograph revealed the planet's signal, making it the lightest planet detected around a solar-type star. The discovery demonstrates that current techniques can detect potentially habitable super-Earth planets around Sun-like stars and habitable Earth-like planets around cooler stars.
An Earth-mass planet orbiting a Centauri BCarlos Bella
1) Researchers detected an Earth-mass planet orbiting the star Alpha Centauri B.
2) The planet has a minimum mass similar to Earth and orbits its star with a period of 3.236 days, within 0.04 astronomical units.
3) This makes it the lightest planet detected orbiting a Sun-like star and the closest exoplanet to our solar system found to date.
The Possible Tidal Demise of Kepler’s First Planetary SystemSérgio Sacani
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet
(1.1RJ, 5.9MJ) orbiting an evolved host star (2.9Re, 1.5Me). Using transit timing measurements from Kepler,
Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate = -
+ P 131 22
20 ms yr−1
, corresponding to an infall timescale P P » 2.5 Myr. We consider other explanations for the
data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed
period derivative implies a tidal quality factor
¢ = ´ -
+ Q 2.50 10 0.62
0.85 4, in good agreement with theoretical
predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire
inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for
the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new
benchmark for understanding tidal physics at the end of the planetary life cycle
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
This document summarizes the discovery of Kepler-413b, a Neptune-sized circumbinary planet orbiting the eclipsing binary star system Kepler-413. The planet has an orbital period of approximately 66 days and an eccentric orbit with a semimajor axis of 0.355 AU. Analysis of the Kepler light curve revealed the planet's orbit is misaligned with the binary star plane by about 2.5 degrees, causing it to sometimes fail to transit one of the stars. The orbital configuration of the system places the planet interior to the habitable zone but its obliquity may undergo fluctuations on precession timescales.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
Similar to Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Gravitational waves from ejection of jet superluminal components and precession of accretion disk dynamically driven by bardeen petterson efect (20)
STUDY OF THE COMET 12P/PONS-BROOKS.A. Q. Vodniza1, 1Director of University of...SOCIEDAD JULIO GARAVITO
ntroduction: This comet was discovered by Jean-
Louis Pons on July 12/1812, and re-discovered by
William Robert Brooks in 1883. It’s believed that
Chinese astronomers could have observed it back in
the year 1300 [1]. This comet will reach its perihelion
on April 21/2024 at a distance of 0.781 AU [2]. It will
get closest to Earth on June 2 of the same year. The
cometary nucleus is approximately 17 +/- 6 kilometers
[3]. The comet is famous for its explosions: at least
seven major explosions have been observed since the
19th century and in 2023 they have been detected on
July 20, October 5, November 1, November 14 [4].
The comet is of the criovolcanic type and produces
explosions that are created by the degassing of the
carbon dioxide in the nucleus. Unlike most comets, the
gas and ice inside this comet accumulate so much that
this celestial object can explode violently, shooting
material called cryomagma through large cracks in the
nucleus’ shell [5].
Methodology:
CAPITULO4_EL_PRINCIPITO:De esta manera supe una segunda cosa muy importante: ...SOCIEDAD JULIO GARAVITO
El Principito – Capítulo 4
De esta manera supe una segunda cosa muy importante: su planeta de origen era apenas más grande que una casa
Esto no podía asombrarme mucho. Sabía muy bien que aparte de los grandes planetas como la Tierra, Júpiter, Marte, Venus, a los cuales se les ha dado nombre, existen otros centenares
de ellos tan pequeños a veces, que es difícil distinguirlos aun con la ayuda del telescopio.
Cuando un astrónomo descubre uno de estos planetas, le da por nombre un número. Le llama, por ejemplo, «el asteroide 3251» ((423624) Udeantioquia)
Teoría Cuántica de
Campos y su Interfaz
con Física de Astro-
Partículas y Astronomía
de Ondas
Gravitacionales.
Editor: Herman J. Mosquera Cuesta.
Co-Editores: Fabián H. Zuluaga Giraldo,
Wilmer Daniel Alfonso P.,
Edgardo J. Marbello Santrich.
INTECH_OPEN/2024.
La ecuación más larga en física
El modelo Lagrangiano es una expresión matemática que resume el Modelo Estándar de física de partículas, que es la teoría más exitosa de las interacciones fundamentales entre partículas elementales.
Se compone de cuatro partes diferentes, cada una de las cuales describe un aspecto diferente del Modelo Estándar.
El modelo lagrangiano está escrito en una notación compacta que utiliza símbolos y operadores de la teoría cuántica de campos, como derivadas covariantes, tensores de intensidad de campo, matrices de Dirac y generadores de grupos de calibre.
También utiliza varias constantes y parámetros que se determinan mediante experimentos, como constantes de acoplamiento, masas y ángulos de mezcla. Es una de las ecuaciones más largas de la física porque contiene muchos términos y factores que explican todas las posibles interacciones y simetrías del modelo estándar.
Fue transcrito por Thomas Gutiérrez, quien lo derivó de Diagrammatica: The Path to Feynman Diagrams de Martinus Veltman.
Cómo usan el baño los astronautas en el espacio? - Abril 4, 2024 - space.comSOCIEDAD JULIO GARAVITO
¿Cómo usan el baño los astronautas en el espacio?
Por Robert Lea
Fuente: https://www.space.com/how-do-astronauts-go-to-bathroom-in-space-toilet-
guide
Publicado el 4 de abril de 2024
¡Para ir con valentía! Los astronautas pueden parecer sobrehumanos, pero tienen
las mismas necesidades básicas que el resto de nosotros, y eso incluye usar el baño
en el espacio.
¿Cómo usan los astronautas el baño en el espacio? Es un poco complicado... (Crédito de la imagen:
Daisy Dobrijevic producida en Canva)
"Hazlo con el traje"
Esas fueron las desconcertantes palabras que el primer estadounidense en el
espacio, Alan Shepherd, escuchó el 5 de mayo de 1961, cuando avisó al equipo de
la plataforma de lanzamiento que necesitaba orinar. Shepherd hizo lo que le
indicaron, orinó en su traje espacial y provocó un cortocircuito en sus biosensores
electrónicos.
El traje espacial de Shepherd no estaba equipado con un sistema de recolección de
orina porque no se esperaba que su misión durara lo suficiente como para que
necesitara orinar.
Información editada y compartida vía:
Elkin Ramiro Mesa Ochoa
Médico - Universidada de Antioquia - Alma Máter UdeA.
Sociedad Julio Garavito para el Estudio de la Astronomía (SJG - Astronomy); Ciudad de Medellín (Distrito Espacial, Especial en Ciencia, Ingeniería, Tecnología, Innovación, Creatividad e Industria Aeroespacial), Antioquia-Departamento Aeroespacial de la República de Colombia, América del Sur.
https://youtube.com/live/y8HxJIFedcM
Agradecemos muy especialmente a Olga Lucía Penagos Eastman, diseñadora gráfica y aficionada a la astronomía, por la elaboración del afiche de invitación a nuestra charla.
Sociedad Julio Garavito para el Estudio de la Astronomía (SJG - Astronomy); Ciudad de Medellín (Distrito Espacial, Especial en Ciencia, Ingeniería, Tecnología, Innovación, Creatividad e Industria Aeroespacial), Antioquia-Departamento Aeroespacial de la República de Colombia, América del Sur.
TO BE HUMAN, IT SEEMS, IS TO SEEK PURPOSE IN OUR
TRANSIENT lives. Many people find meaning in the eyes of their children
or in the words of Scripture, but I discovered it on a beach outside a Hyatt
Regency in Aruba. I had journeyed south that winter of 1998 to escape the
snows of Boston and, more notably, to take in nature’s grandest spectacle, a
total solar eclipse, which would cross the Caribbean on a Thursday
afternoon in late February. As a science journalist, I thought I knew what to
expect. For 174 seconds, the blue sky would blacken, stars would appear,
and the sun would manifest its ethereal outer atmosphere, the solar corona.
What I had not anticipated was my own intense reaction to the display.
For three glorious minutes, I felt transported to another planet, indeed to a higher plane of reality, as my consciousness departed the earth and I gaped at an alien sky. Above me, in the dim vault of the heavens, shone an incomprehensible object. It looked like an enormous wreath woven from silvery thread, and it hung suspended in the immensity of space, shimmering.
As I stood transfixed by this vision, I felt something I had never experienced before—a visceral connection to the universe—and I became an umbraphile, an eclipse chaser, one who has since obsessively stalked the moon’s shadow —across Europe, Asia, Australia—for yet a few more fleeting moments of lunar nirvana.
Medellín, viernes 23 de febrero de 2024.
CITACIÓN A LA ASAMBLEA ANUAL ORDINARIA
La junta directiva de la SOCIEDAD JULIO GARAVITO convoca a todos los miembros a la Asamblea Anual Ordinaria, que se efectuará el día sábado 23 de marzo de 2024 a las 10:00 a.m. en forma virtual, en la plataforma: https://meet.jit.si/asambleasjg2024.
Nota: La clave de acceso a la sala de la asamblea será compartida a los socios el día sábado 23 de marzo con dos horas de anticipación en el grupo de WhatsApp de la Sociedad.
El orden del día será el siguiente:
ORDEN DEL DÍA
1º.- Verificación del quórum.
2º.- Nombramiento de la Comisión de Aprobación del Acta. 3º.- Aprobación del Orden del Día.
4º.- Informe del Director. 5º.- Informe del Tesorero.
6º.- Informe del Revisor Fiscal.
7º.- Designación de la nueva Junta Directiva. 8º.- Designación del Revisor Fiscal.
9º.- Designación del Tesorero. 10º.-Proposiciones y varios.
NOTA:
Se recomienda estar a la hora indicada; además se recuerda que cada miembro de número puede representar por escrito sólo a otro miembro de número que no pueda asistir.
Atentamente:
JUNTA DIRECTIVA SOCIEDAD JULIO GARAVITO.
https://youtube.com/live/rIIkZoSgljs
Agradecemos a Paola Restrepo, Astrónoma y Artísta por su apoyo en la elaboración del afiche de invitación a nuestra charla de la Sociedad.
En ésta charla, Mujeres en la astronomía:
Recordaremos a algunas mujeres que han escogido observar el cielo, y explicarlo, y cuyos logros han sido reconocidos.
También abriremos un espacio para conversar sobre la situación actual de las mujeres que quieren dedicarse a la Astronomía y a las Ciencias Espaciales.
Por:
Luz Angela Cubides González.
Astrónoma (2004), Magíster en Hermenéutica Literaria (2013) y docente.
Amiga Sociedad Julio Garavito para el Estudio de la Astronomía (SJG - Astronomy); Ciudad de Medellín (Distrito Espacial, Especial en Ciencia, Ingeniería, Tecnología, Innovación, Creatividad e Industria Aeroespacial), Antioquia-Departamento Aeroespacial de la República de Colombia, América del Sur.
Portada y contraportada de este Anuario ilustran un resultado
excepcional obtenido durante 2023: la imagen de la sombra central,
disco de acrecimiento y chorro energético en el agujero negro de la
galaxia M87. En la imagen se aprecia directamente cómo se eyecta el
chorro a partir del material que se acreta sobre el agujero negro super-
masivo. El pionero resultado fue obtenido con la red global de telesco-
pios de ondas milimétricas (GMVA), red en la que los radiotelescopios
de Yebes y del IRAM juegan un papel central. Y en el funcionamiento
de estos instrumentos resulta crucial la labor de su personal técnico
y de sus astrónomos, entre ellos los del OAN que prestan su apoyo al
Observatorio de Yebes.
También en 2023, el IGN ha realizado un importantísimo esfuerzo
para mejorar ambos radiotelescopios: el de 40-m en Yebes y el de
30-m del IRAM en Pico Veleta (Granada). En el primero se ha instalado
un espejo secundario con movimiento de balanceo (wobbler) y en el
segundo un nuevo sistema de servomecanismos. Cofinanciadas con
fondos FEDER, estas actuaciones permitirán aumentar la precisión de
ambos instrumentos al límite de las posibilidades actuales de la inge-
niería. Gracias a estas mejoras, se garantiza que los radiotelescopios
permanezcan en la vanguardia científico-tecnológica durante varias
décadas, lo que permitirá a nuestros astrónomos seguir participando
en muchos más descubrimientos y observaciones revolucionarias.
Otro hito importante alcanzado en 2023, de interés para toda la
radioastronomía nacional, ha sido la adhesión formal de España
al tratado internacional del Square Kilometre Array (SKA). De esta
forma, las empresas nacionales participarán en la construcción de
este colosal radiotelescopio, que ya ha comenzado en Australia y en
Sudáfrica, y nuestros astrónomos podrán realizar, desde primera
línea, observaciones pioneras que sin duda transformarán nuestro
conocimiento del universo.
Los artículos de divulgación no pueden faltar en este Anuario.
Ya que pronto se cumplirán 50 años del inicio de la construcción
del Observatorio de Yebes, su director, Pablo de Vicente, nos ilustra
sobre el enorme contenido tecnológico involucrado en la radioastro-
nomía, poniendo énfasis en los importantísimos desarrollos reali-
zados en Yebes. Por su parte, nuestra astrónoma Marina Rodríguez
Baras trata un tema de candente actualidad: la búsqueda de vida en
el sistema solar.
Una guía de los mejores eventos astronómicos de 2024: cuándo, dónde y cómo fo...SOCIEDAD JULIO GARAVITO
Este documento proporciona una guía detallada de los principales eventos astronómicos que tendrán lugar en 2024, incluidos eclipses, lluvias de estrellas, planetas visibles y más. Incluye un calendario mes a mes de los eventos, con información sobre fechas, horas y lugares de visibilidad. Además, ofrece consejos sobre cómo planificar la observación y fotografía de estos eventos utilizando la aplicación PhotoPills. El objetivo es ayudar a los lectores a aprovechar al máximo las oportunidades
Article
Estimating Flight Characteristics of Anomalous
Unidentified Aerial Vehicles
Kevin H. Knuth 1,2,* , Robert M. Powell 2 and Peter A. Reali 2
1 Department of Physics, University at Albany (SUNY), Albany, NY 12222, USA
2 Scientific Coalition for UAP Studies (SCU), Fort Myers, FL 33913, USA;
robertmaxpowell@gmail.com (R.M.P.); preali@cableone.net (P.A.R.)
* Correspondence: kknuth@albany.edu
Received: 21 August 2019; Accepted: 21 September 2019; Published: 25 September 2019
Abstract: Several Unidentified Aerial Phenomena (UAP) encountered by military, commercial, and
civilian aircraft have been reported to be structured craft that exhibit ‘impossible’ flight characteristics.
We consider a handful of well-documented encounters, including the 2004 encounters with the
Nimitz Carrier Group off the coast of California, and estimate lower bounds on the accelerations
exhibited by the craft during the observed maneuvers. Estimated accelerations range from almost
100 g to 1000s of gs with no observed air disturbance, no sonic booms, and no evidence of excessive
heat commensurate with even the minimal estimated energies. In accordance with observations,
the estimated parameters describing the behavior of these craft are both anomalous and surprising.
The extreme estimated flight characteristics reveal that these observations are either fabricated or
seriously in error, or that these craft exhibit technology far more advanced than any known craft on
Earth. In many cases, the number and quality of witnesses, the variety of roles they played in the
encounters, and the equipment used to track and record the craft favor the latter hypothesis that
these are indeed technologically advanced craft. The observed flight characteristics of these craft
are consistent with the flight characteristics required for interstellar travel, i.e., if these observed
accelerations were sustainable in space, then these craft could easily reach relativistic speeds within a
matter of minutes to hours and cover interstellar distances in a matter of days to weeks, proper time.
Keywords: UAP; UAV; UFO; Nimitz; Tic-Tac
Hola Sociedad Julio Garavito para el Estudio de la Astronomía (SJG-Astronomy),
Soy Silvia, especialista en conservación de WWF Colombia, y me complace enormemente compartir con Ustedes esta guía que hicimos con mucho amor y dedicación para que juntos podamos explorar a los maravillosos animales que habitan en nuestra hermosa Colombia. 🦋🌳
A través del arte del origami, podrás crear tu propia representación de un ágil jaguar o una imponente ballena, sin importar el color ni que quede perfecto y lo mejor de todo, puedes hacerlo con papel reciclado.
¡Esta guía es como tener un pedacito de la naturaleza en tus manos! 🌿
Silvia Vejarano
WWF Colombia, Bogotá Oficina Bogotá Carrera 10 A # 69 A 44, Bogotá, Cundinamarca 111221, Colombia, 443 1550
El cielo celebra la época decembrina con la lluvia de meteoros de Las Gemínidas, la más
abundante del año. Así es, la noche del miércoles 13 de diciembre desde las 9 p.m. en adelante
pudiéramos comenzar a ver los luminosos trazos meteóricos de “Las Gemínidas”, para este año
tenemos la fortuna de que un día antes ocurrirá la Luna Nueva, lo que significa que no tendremos
el brillo de la luna opacando la visualización de los meteoros. Por lo que inclusive desde el mismo
atardecer pudiéramos estar pendientes a ver si captamos alguna Gemínida.
Para este año 2023 el máximo de actividad ocurrirá las 2:00 pm del jueves 14 de diciembre, así
tanto los días 13 y el 14 de diciembre, desde que salga la constelación de Géminis, por el horizonte
oriental a las 8 pm., estaremos en la posibilidad de disfrutar de este espectáculo celeste durante
toda la noche; se espera que en las mejores condiciones de visibilidad, puedan observarse hasta
150 meteoros por hora, según la Organización Internacional de Meteoros (IMO), sin embargo esto
disminuye drásticamente con la contaminación lumínica del lugar de observación.
Inforamción Compartida por:
Enrique Torres.
Divulgador de Astronomía, Ágora del Cosmos
Información compartida por Enrique Torres:
Amigo Sociedad Julio Garavito para el Estudio de la Astronomía (SJG - Astronomy); Ciudad de Medellín (Distrito Espacial, Especial en Ciencia, Ingeniería, Tecnología, Innovación, Creatividad e Industria Aeroespacial), Departamento de Antioquia, República de Colombia, América del Sur.
Rover IUE: exploration of the concept from
human factors
León Jaime Restrepo Quirós, José Andrés Zuluaga Ramírez
Grupo de investigación en tecnologías emergentes,
sostenibles e inteligentes – GITESI
Línea de automatización industrial
Facultad de ingeniería, Institución Universitaria de Envigado
Gráficas Conjución Luna Pleyades utilizando el Stelarium 23.3
Por:
Elkin Ramiro Mesa Ochoa
Médico - Universidada de Antioquia - Alma Máter UdeA.
Sociedad Julio Garavito para el Estudio de la Astronomía (SJG - Astronomy); Ciudad de Medellín (Distrito Espacial, Especial en Ciencia, Ingeniería, Tecnología, Innovación, Creatividad e Industria Aeroespacial), Antioquia-Departamento Aeroespacial de la República de Colombia, América del Sur.
EL ASTEROIDE APOPHIS
Por: Alberto Quijano Vodniza
Master in Physics - University of Puerto Rico
Director of "University of Narino Observatory"
Member of the "American Astronomical Society"
Es común a través de las redes y de algunos medios de comunicación, publicar noticias alarmantes
que indican: “un asteroide rozará a la Tierra próximamente”. Esas publicaciones están afirmando
en definitiva que habrá colisión entre un cuerpo celeste y nuestro planeta, lo cual afortunadamente
es falso! Y ahora le tocó el turno al famoso asteroide APOPHIS, y muchos medios ya están
divulgando noticias que se apartan de la realidad!
El asteroide APOPHIS tiene un diámetro de aproximadamente 270 metros, y fue descubierto en la
Navidad del 2004. Se hizo famoso en aquel entonces por la predicción de su gran proximidad a la
Tierra que ocurrirá el 13 de abril del 2029; pasará a tan sólo 32.000 kilómetros de nuestro planeta,
mucho más cerca que los satélites artificiales, pero evidentemente muy lejos de la atmósfera
terrestre. Los primeros cálculos realizados con pocos datos observacionales, estimaban una gran
probabilidad de colisión con la Tierra, pero con el transcurso de los años se han tomado gran
cantidad de datos adicionales, con los cuales ya se ha refinado muy bien la órbita del asteroide, y
ahora se concluye todo lo contrario. Como en el año 2029 el acercamiento a la Tierra será bastante
cerrado (pero a una distancia segura), se estimó que el campo gravitacional terrestre podría
modificar la órbita del asteroide en un grado tal, que habría una probabilidad de colisión con nuestro
planeta en el año 2036 o 2068. Por ese motivo, para investigar mucho más la dinámica del asteroide,
se aprovechó los primeros días del mes de marzo del año 2021 para tomar nuevos datos de
APOPHIS, y Científicos de la Universidad de Arizona y de NASA organizaron el grupo internacional
denominado “99942 APOPHIS 2021 OBSERVING CAMPAIGN”, dirigido por el científico Dr. Vishnu
Reddy.
https://iawn.net/obscamp/Apophis/index.shtml
Aunque el gran Radiotelescopio de Arecibo desafortunadamente colapsó en diciembre del 2020, y
no pudo usarse para observaciones de radar,se utilizaron otros instrumentos: El radiotelescopio
situado en California denominado “The Deep Space Network’s Goldstone Complex” y “The Green
Bank Telescope” ubicado en Virginia Occidental-USA.
Con la gran cantidad de datos de fotometría, astrometría y radar capturados en fechas cercanas al
5 de marzo del año 2021, época en la cual APOPHIS estuvo aproximadamente a 17 millones de
kilómetros de la Tierra, se calculó mucho mejor la órbita de APOPHIS, se realizaron además muchas
simulaciones en computador, y se llegó a la conclusión final que NO EXISTE ninguna probabilidad
que este asteroide colisione con la Tierra.
Información compartida por:
Alberto Quijano Vodniza
Observatorio de la Universidad de Nariño - Pasto - Colombia.
https://observatorioastronomico.udenar.edu.co/
Amigo Sociedad Julio Garavito
Es este el cometa más extraño que hay - Cometa 12P Pons-Brooks - Nov 20, 2023...SOCIEDAD JULIO GARAVITO
¿ES ESTE EL COMETA MÁS EXTRAÑO QUE HAY?
El cometa 12P/Pons-Brooks sigue desconcertando a los astrónomos, que están
vigilando las consecuencias de su cuarta gran erupción criovolcánica en 2023. Las
erupciones anteriores de julio y octubre produjeron "cuernos de diablo".
Dandelion Hashtable: beyond billion requests per second on a commodity serverAntonios Katsarakis
This slide deck presents DLHT, a concurrent in-memory hashtable. Despite efforts to optimize hashtables, that go as far as sacrificing core functionality, state-of-the-art designs still incur multiple memory accesses per request and block request processing in three cases. First, most hashtables block while waiting for data to be retrieved from memory. Second, open-addressing designs, which represent the current state-of-the-art, either cannot free index slots on deletes or must block all requests to do so. Third, index resizes block every request until all objects are copied to the new index. Defying folklore wisdom, DLHT forgoes open-addressing and adopts a fully-featured and memory-aware closed-addressing design based on bounded cache-line-chaining. This design offers lock-free index operations and deletes that free slots instantly, (2) completes most requests with a single memory access, (3) utilizes software prefetching to hide memory latencies, and (4) employs a novel non-blocking and parallel resizing. In a commodity server and a memory-resident workload, DLHT surpasses 1.6B requests per second and provides 3.5x (12x) the throughput of the state-of-the-art closed-addressing (open-addressing) resizable hashtable on Gets (Deletes).
Connector Corner: Seamlessly power UiPath Apps, GenAI with prebuilt connectorsDianaGray10
Join us to learn how UiPath Apps can directly and easily interact with prebuilt connectors via Integration Service--including Salesforce, ServiceNow, Open GenAI, and more.
The best part is you can achieve this without building a custom workflow! Say goodbye to the hassle of using separate automations to call APIs. By seamlessly integrating within App Studio, you can now easily streamline your workflow, while gaining direct access to our Connector Catalog of popular applications.
We’ll discuss and demo the benefits of UiPath Apps and connectors including:
Creating a compelling user experience for any software, without the limitations of APIs.
Accelerating the app creation process, saving time and effort
Enjoying high-performance CRUD (create, read, update, delete) operations, for
seamless data management.
Speakers:
Russell Alfeche, Technology Leader, RPA at qBotic and UiPath MVP
Charlie Greenberg, host
TrustArc Webinar - 2024 Global Privacy SurveyTrustArc
How does your privacy program stack up against your peers? What challenges are privacy teams tackling and prioritizing in 2024?
In the fifth annual Global Privacy Benchmarks Survey, we asked over 1,800 global privacy professionals and business executives to share their perspectives on the current state of privacy inside and outside of their organizations. This year’s report focused on emerging areas of importance for privacy and compliance professionals, including considerations and implications of Artificial Intelligence (AI) technologies, building brand trust, and different approaches for achieving higher privacy competence scores.
See how organizational priorities and strategic approaches to data security and privacy are evolving around the globe.
This webinar will review:
- The top 10 privacy insights from the fifth annual Global Privacy Benchmarks Survey
- The top challenges for privacy leaders, practitioners, and organizations in 2024
- Key themes to consider in developing and maintaining your privacy program
For the full video of this presentation, please visit: https://www.edge-ai-vision.com/2024/06/temporal-event-neural-networks-a-more-efficient-alternative-to-the-transformer-a-presentation-from-brainchip/
Chris Jones, Director of Product Management at BrainChip , presents the “Temporal Event Neural Networks: A More Efficient Alternative to the Transformer” tutorial at the May 2024 Embedded Vision Summit.
The expansion of AI services necessitates enhanced computational capabilities on edge devices. Temporal Event Neural Networks (TENNs), developed by BrainChip, represent a novel and highly efficient state-space network. TENNs demonstrate exceptional proficiency in handling multi-dimensional streaming data, facilitating advancements in object detection, action recognition, speech enhancement and language model/sequence generation. Through the utilization of polynomial-based continuous convolutions, TENNs streamline models, expedite training processes and significantly diminish memory requirements, achieving notable reductions of up to 50x in parameters and 5,000x in energy consumption compared to prevailing methodologies like transformers.
Integration with BrainChip’s Akida neuromorphic hardware IP further enhances TENNs’ capabilities, enabling the realization of highly capable, portable and passively cooled edge devices. This presentation delves into the technical innovations underlying TENNs, presents real-world benchmarks, and elucidates how this cutting-edge approach is positioned to revolutionize edge AI across diverse applications.
Have you ever been confused by the myriad of choices offered by AWS for hosting a website or an API?
Lambda, Elastic Beanstalk, Lightsail, Amplify, S3 (and more!) can each host websites + APIs. But which one should we choose?
Which one is cheapest? Which one is fastest? Which one will scale to meet our needs?
Join me in this session as we dive into each AWS hosting service to determine which one is best for your scenario and explain why!
Main news related to the CCS TSI 2023 (2023/1695)Jakub Marek
An English 🇬🇧 translation of a presentation to the speech I gave about the main changes brought by CCS TSI 2023 at the biggest Czech conference on Communications and signalling systems on Railways, which was held in Clarion Hotel Olomouc from 7th to 9th November 2023 (konferenceszt.cz). Attended by around 500 participants and 200 on-line followers.
The original Czech 🇨🇿 version of the presentation can be found here: https://www.slideshare.net/slideshow/hlavni-novinky-souvisejici-s-ccs-tsi-2023-2023-1695/269688092 .
The videorecording (in Czech) from the presentation is available here: https://youtu.be/WzjJWm4IyPk?si=SImb06tuXGb30BEH .
The Microsoft 365 Migration Tutorial For Beginner.pptxoperationspcvita
This presentation will help you understand the power of Microsoft 365. However, we have mentioned every productivity app included in Office 365. Additionally, we have suggested the migration situation related to Office 365 and how we can help you.
You can also read: https://www.systoolsgroup.com/updates/office-365-tenant-to-tenant-migration-step-by-step-complete-guide/
Fueling AI with Great Data with Airbyte WebinarZilliz
This talk will focus on how to collect data from a variety of sources, leveraging this data for RAG and other GenAI use cases, and finally charting your course to productionalization.
Best 20 SEO Techniques To Improve Website Visibility In SERPPixlogix Infotech
Boost your website's visibility with proven SEO techniques! Our latest blog dives into essential strategies to enhance your online presence, increase traffic, and rank higher on search engines. From keyword optimization to quality content creation, learn how to make your site stand out in the crowded digital landscape. Discover actionable tips and expert insights to elevate your SEO game.
Introduction of Cybersecurity with OSS at Code Europe 2024Hiroshi SHIBATA
I develop the Ruby programming language, RubyGems, and Bundler, which are package managers for Ruby. Today, I will introduce how to enhance the security of your application using open-source software (OSS) examples from Ruby and RubyGems.
The first topic is CVE (Common Vulnerabilities and Exposures). I have published CVEs many times. But what exactly is a CVE? I'll provide a basic understanding of CVEs and explain how to detect and handle vulnerabilities in OSS.
Next, let's discuss package managers. Package managers play a critical role in the OSS ecosystem. I'll explain how to manage library dependencies in your application.
I'll share insights into how the Ruby and RubyGems core team works to keep our ecosystem safe. By the end of this talk, you'll have a better understanding of how to safeguard your code.
Skybuffer SAM4U tool for SAP license adoptionTatiana Kojar
Manage and optimize your license adoption and consumption with SAM4U, an SAP free customer software asset management tool.
SAM4U, an SAP complimentary software asset management tool for customers, delivers a detailed and well-structured overview of license inventory and usage with a user-friendly interface. We offer a hosted, cost-effective, and performance-optimized SAM4U setup in the Skybuffer Cloud environment. You retain ownership of the system and data, while we manage the ABAP 7.58 infrastructure, ensuring fixed Total Cost of Ownership (TCO) and exceptional services through the SAP Fiori interface.
Driving Business Innovation: Latest Generative AI Advancements & Success StorySafe Software
Are you ready to revolutionize how you handle data? Join us for a webinar where we’ll bring you up to speed with the latest advancements in Generative AI technology and discover how leveraging FME with tools from giants like Google Gemini, Amazon, and Microsoft OpenAI can supercharge your workflow efficiency.
During the hour, we’ll take you through:
Guest Speaker Segment with Hannah Barrington: Dive into the world of dynamic real estate marketing with Hannah, the Marketing Manager at Workspace Group. Hear firsthand how their team generates engaging descriptions for thousands of office units by integrating diverse data sources—from PDF floorplans to web pages—using FME transformers, like OpenAIVisionConnector and AnthropicVisionConnector. This use case will show you how GenAI can streamline content creation for marketing across the board.
Ollama Use Case: Learn how Scenario Specialist Dmitri Bagh has utilized Ollama within FME to input data, create custom models, and enhance security protocols. This segment will include demos to illustrate the full capabilities of FME in AI-driven processes.
Custom AI Models: Discover how to leverage FME to build personalized AI models using your data. Whether it’s populating a model with local data for added security or integrating public AI tools, find out how FME facilitates a versatile and secure approach to AI.
We’ll wrap up with a live Q&A session where you can engage with our experts on your specific use cases, and learn more about optimizing your data workflows with AI.
This webinar is ideal for professionals seeking to harness the power of AI within their data management systems while ensuring high levels of customization and security. Whether you're a novice or an expert, gain actionable insights and strategies to elevate your data processes. Join us to see how FME and AI can revolutionize how you work with data!
5th LF Energy Power Grid Model Meet-up SlidesDanBrown980551
5th Power Grid Model Meet-up
It is with great pleasure that we extend to you an invitation to the 5th Power Grid Model Meet-up, scheduled for 6th June 2024. This event will adopt a hybrid format, allowing participants to join us either through an online Mircosoft Teams session or in person at TU/e located at Den Dolech 2, Eindhoven, Netherlands. The meet-up will be hosted by Eindhoven University of Technology (TU/e), a research university specializing in engineering science & technology.
Power Grid Model
The global energy transition is placing new and unprecedented demands on Distribution System Operators (DSOs). Alongside upgrades to grid capacity, processes such as digitization, capacity optimization, and congestion management are becoming vital for delivering reliable services.
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Building Production Ready Search Pipelines with Spark and MilvusZilliz
Spark is the widely used ETL tool for processing, indexing and ingesting data to serving stack for search. Milvus is the production-ready open-source vector database. In this talk we will show how to use Spark to process unstructured data to extract vector representations, and push the vectors to Milvus vector database for search serving.
Energy Efficient Video Encoding for Cloud and Edge Computing Instances
Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Gravitational waves from ejection of jet superluminal components and precession of accretion disk dynamically driven by bardeen petterson efect
1. 8th Alexander Friedmann International Seminar
on Gravitation and Cosmology
International Journal of Modern Physics: Conference Series
Vol. 3 (2011) 482–493
c World Scientific Publishing Company
DOI: 10.1142/S2010194511001000
GRAVITATIONAL WAVES FROM EJECTION OF JET
SUPERLUMINAL COMPONENTS AND PRECESSION OF
ACCRETION DISKS DYNAMICALLY DRIVEN BY
BARDEEN-PETTERSON EFFECT
HERMAN J. MOSQUERA CUESTA,1,2 LUIS A. SANCHEZ,3 DANIEL ALFONSO PARDO,3 ,
´
ANDERSON CAPRONI,4 ZULEMA ABRAHAM5 and LUIS HENRY QUIROGA NUNEZ6˜
1 Departmento de F´ ısica, Universidade Estadual Vale do Acara´, Avenida da Universidade 850,
u
Campus da Betˆnia, CEP 62.040-370, Sobral, Cear´, Brazil
a a
2 Instituto de Cosmologia, Relatividade e Astrof´sica (ICRA-BR)
ı
Centro Brasileiro de Pesquisas F´ ısicas, Rua Dr. Xavier Sigaud 150, CEP 22290-180 Urca, Rio
de Janeiro, RJ, Brazil
3 Escuela de F´ ısica, Universidad Nacional de Colombia, Sede Medell´ A.A. 3840, Medell´
ın, ın,
Colombia
4 N´cleo de Astrof´
u ısica Te´rica (NAT), P´s-gradua¸ao e Pesquisa, Universidade Cruzeiro do Sul
o o c˜
Rua Galv˜o Bueno 868, Liberdade 01506-000, S˜o Paulo, SP, Brasil
a a
5 Instituto de Astronomia, Geof´ ısica e Ciˆncias Atmosf´ricas, Universidade de S˜o Paulo
e e a
Rua do Mat˜o 1226, Cidade Universit´ria, CEP 05508-900, S˜o Paulo, SP, Brazil
a a a
6 Departamento de F´ ısica, Universidad Nacional de Colombia, Sede Bogot´, A.A. 76948,
a
Bogot´, D.C., Colombia
a
Received 1 July 2011
Revised 11 July 2011
Jet superluminal components are recurrently ejected from active galactic nuclei, micro-
quasars, T-Tauri star, and several other astrophysical systems, including gamma-ray
burst sources. The mechanism driving this powerful phenomenon is not properly settled
down yet. In this article we suggest that ejection of ultrarelativistic components may be
associated to the superposition of two actions: precession of the accretion disk induced
by the Kerr black hole (KBH) spin, and fragmentation of the tilted disk; this last being
an astrophysical phenomenon driven by the general relativistic Bardeen-Petterson (B-P)
effect. As fragmentation of the accretion disk takes place at the B-P transition radius, the
incoming material that get trapped in this sort of Lagrange internal point will forcibly
precess becoming a source of continuous, frequency-modulated gravitational waves. At
resonance blobs can be expelled at ultrarelativistic velocities from the B-P radius. The
launching of superluminal components of jets should produce powerful gravitational wave
(GW) bursts during its early acceleration phase, which can be catched on the fly by
current GW observatories. Here we compute the characteristic amplitude and frequency
of such signals and show that they are potentially detectable by the GW observatory
LISA.
Keywords: Active galaxies; galaxies nuclei; galaxies quasars; black hole physics.
Pacs: 97.10.Gz, 04.30.-w, 04.30.Nn
482
2. Gravitational Waves from Accretion Disks 483
1. Introduction
Radio interferometric observations of active galactic nuclei (AGN – n radio galaxies,
blazars, Seyfert I and II galaxies, etc.), micro-quasars and T-Tauri stars exhibit
apparently stationary bright cores enshrouded by faint haloes, kiloparsec (kpc) jets,
and superluminal parsec (pc) components that appear to travel following curved
trajectories with spatially changing velocities. High spatial resolution observations
of AGN show that the superluminal ejected material is moving out from their very
central regions: the core. The resultant structure is seen in the sky as pairs of curved
jets that extend from several pc, kpc, and even megaparsecs (Mpc) distance scales
from the AGN core. Jet material seems to be constituted of a plasma composed
of electron-positron pairs plus some baryons. The jet morphology is diverse, some
of them presenting features that resembles spirals in the sky. These characteristics
were interpreted by several authors as due to helical motion of the components along
the jet. In an alternative view,1,2 it was proposed that such helicoidal appearance of
the jet may be due to precession of the disk-jet structure. A few other proposals to
cope with the observations are at disposal, but the actual mechanism driving this
phenomenology is nonetheless not yet conclusively established.
The first systematic study on the Bardeen-Petterson (B-P) effect as the potential
driving engine (mechanism) behind the observed dynamics of AGN was presented
in Ref. 3. (See also Refs. 4-7 in which we extend these results to the analysis of
some other specific AGN sources, and to confront the B-P scenario for AGN with
alternative mechanisms to explain the helicoidal motion of jet components and the
disk warping.) Therein we have shown that for a large sample of AGN the observed
disk and/or jet precession can be consistently explained as driven by the B-P effect.
As described below, a torus encircling a rotating (Kerr) supermassive black hole
(SMBH), as the state-of-the-art envisions AGN, may lead a rotating SMBH into
a dramatic dynamical stage, known as suspended accretion state (SAS),8 in which
most of the SMBH spin energy can be released through gravitational radiation due
to the spin-disk magnetic field coupling. As SAS can develop only in a very compact
black hole (BH)-Torus structure,8 we argue in a paper related to this9 that in the
case of AGN the Bardeen-Petterson effect is a necessary and sufficient mechanism
to produce SAS.a In that related paper9 we compute the emission of gravitational
waves (GW) generated by the AGN torus dynamics as driven by the B-P effect.
In a tilted accretion disk orbiting around a rotating BH, the B-P effect creates
a gap, or discontinuity, which is known as transition region or B-P radius. Matter
arriving from the outer part of the disk can pile-up at this radius because of the
magneto-centrifugal barrier creating a sort of Lagrange internal point. Consequently,
the accumulated material can condensate in a blob or knot whereby becoming a
source of continuous GW due to its orbital motion around the central BH at the
a It worths to notice that the physical mechanism that could give origin to disk breaking and
precession in AGN and related astrophysical systems was not properly identified in Ref. 10.
3. 484 H. J. Mosquera Cuesta et al.
B-P radius. It also radiates GW upon being launched into space at ultrarelativistic
velocity along the instantaneous jet direction (which explains why jets appear to
be helical, as any component ejection ramdonly points out different directions in
space). In this explanatory scenario for the observed AGN dynamics, we discuss the
characteristics of those GW signals.
2. Bardeen-Petterson Effect in AGN
The frame dragging produced by a Kerr black hole, known as Lense-Thirring effect,
leads a particle to precess (and nutate) if its orbital plane intersects the BH equato-
rial plane, to which the BH angular momentum, JBH , is perpendicular. The ampli-
tude of the precession angular velocity decreases as the third power of the distance,
i.e., ωL−T ∝ r−3 , and becomes negligible at large distances from the KBH. If a
viscous accretion disk is inclined with respect to the equatorial plane of the Kerr
black hole, the differential precession will produce warps in the disk. The inter-
twined action of the Lense-Thirring effect and the internal viscosity of the accretion
disk drives the disk to break apart at a special distance from the KBH known as
Bardeen-Petterson radius, whilst the coupling of the gravitational rotating field to
the inner disk angular momentum enforces the spin axis of the inner accretion disk
to align with the angular momentum axis of the Kerr black hole, in a time scale
which depends on several parameters of the system. This is known as the Bardeen-
Petterson effect11 and affects mainly the innermost part of the disk, while its outer
parts tend to remain in its original configuration due to the short range of the Lense-
Thirring effect. The transition region between these two regimes is referred to as
B-P radius, and its exact location depends on the Mach number of the accretion
disk. (The attentive reader is addressed to Ref. 3 for further details and a list of
references on this astrophysical effect.)
2.1. Kerr spacetime compactness: Modeling Qsr 3C 345 : Sgr A
The disk dynamics caused by the B-P effect thus relates the total torque T applied
to the accretion disk to the disk precession frequency ωprec or period Pprec , and its
total angular momentum Ld . The fundamental relation turns out to be (see Ref. 3
for the derivation of this formula, and further details)
ξout −1 3
Pprec ξms Σd (ξ) [Υ(ξ)] ξ dξ
= KP , (1)
(ξ)Ψ(ξ) [Υ(ξ)]−2 ξ 3 dξ
MBH ξout
ξms
Σd
where KP = 1.5×10−38 s g−1 , Σd the disk surface density, ξ = r/Rg a dimensionless
variable, ξout = Rout /Rg , Υ(ξ) = ξ 3/2 +a∗ and Ψ(ξ) = 1− 1 − 4a∗ ξ −3/2 + 3a2 ξ −2 ,
∗
with a∗ the spin parameter of KBH .
As such, Eq. (1) is parameterized by the ratio of the precession period to the
black hole mass, which in fact is related to a fundamental invariant of the Kerr
metric (see discussion below). As one can see from Eq. (1), the precession period
4. Gravitational Waves from Accretion Disks 485
depends on how the disk surface density Σd varies with the radius. In what follows
we take as an AGN model the source quasar 3C 345. In the search for a disk model
driven by the B-P effect able to reproduce both the observed period and the inferred
mass of the BH in 3C 345, we have modelled the torus by using a power-law function
such as Σd (ξ) = Σ0 ξ s , and also an exponential function like Σd (ξ) = Σ0 eσξ , where
Σ0 , s and σ are arbitrary constants (see Fig. 1 for the results).
One can verify that in the case of 3C 345 the numerical solutions matching
the observed Pprec /MBH ratio favors the spin parameter in the range (prograde)
0.20 ≥ a∗ ≤ −0.35 (retrograde); for a power-law disk of index s = −2. These
results combined with the independent search for the size of the B-P radius tightly
Power-law surface density - 3C 345 Exponential-law surface density - 3C 345
1 1
-1
100
s=0
100
s=2
s=0
s=
1.1
2
=-
0 Rm
1.1
0 Rm
s
Rm
s=2
R ms
s
/R g
s
s
/R g
/R g
0.5
/R g
0.5
black hile spin
black hole spin
-0.4 s = -1
s = -2
0 0
-0.6
s=2 s = -1
s = -2 s = -2
-0.8 s=0
-0.5 -0.5
s = -1
-1 s = 2, s = 0
0.9 1 1.1
-1 -1
1 2 3 1 2 3
log(Rout/Rg) log(Rout/Rg)
Power-law surface density - Sgr A* Exponential-law surface density - Sgr A*
1 1
100
100
1.1
0
1.1
0
R ms
R ms
Rm
Rm
-1
s=0
/R g
s=
s
/R g
s=2
/R g
s
0.5
/R g
0.5
black hile spin
black hole spin
s = -2
0 0
s=
-2
s=
s=0
s=2
-0.5 -0.5
-1
-1 -1
1 2 3 1 2 3
log(Rout/Rg) log(Rout/Rg)
Fig. 1. Isocontours (in logarithmic scale) of the spin-induced precession period normalised by the
BH mass (in units of yr M−1 ), for 3C 345 disk models with power-law and exponential density
profiles (left and right panels, respectively). In this case, solutions compatible with observations
favor a system with a∗ ≥ 0.20 and a∗ ≤ −0.35, correspondingly. Indeed, in this source a full
analysis shows that the spin of the black hole appears to be a∗ = −0.2, that is 3C 345 harbours
a counter-rotating (w.r.t. the accretion disk) Kerr black hole. A similar plot is also shown for the
solution in the case of the KBH in Sgr A . Notice the inner and outer radii limits imposed by the
observations.
5. 486 H. J. Mosquera Cuesta et al.
constraint the BH spin in 3C 345 to the value a∗ −0.20, which means that it is
counterotating w.r.t. disk angular momentum. It appears to be clear that the overall
analysis based on B-P effect also provides an insight on the physical properties of
its accretion disk.
Next we discuss the generation of GWs through the B-P mechanism. To this
purpose, we first stress that the compactness of a rotating BH-Torus system [Eq. (1)],
an example of a Kerr space-time, the ratio of rotational energy to linear size of the
system is an invariant feature, say C, under rescaling of the BH mass. Formally, it
reads
EGW
fGW dE = C fGWi ∆Ei . (2)
0 i
Because of this, one can expect that a physics, essentially similar to that developed
by van Putten et al.12 for the case of stellar-mass BHs as sources of Gamma-Ray
Bursts and GWs, can take place in this size-enlarged version describing the SMBH-
Torus in quasar 3C 345. Indeed, according to Ref. 13 a similar physics seems to
dominate the source Sgr A∗ , which is said to harbour a SMBH-torus system in
the center of our Galaxy. In the case of Sgr A∗ , the rise time for flaring should
vary from half of, to at least a few times, the period of the vertical oscillations.
This parameter has been estimated to be on the order of ∆Pvert = 350 − 1000 s.
F
Meanwhile, the total duration of the flare (F ) should be about a few times the
period of the radial oscillations, a parameter which has been estimated to be on
the range ∆Prad = 40 − 120 min! These timescales have been measured by both
F
Chandra and XMM-Newton X-ray Telescopes.15,16
14
3. GWs from Ultra Relativistic Acceleration of Jet Components in
AGN Dynamically Driven by B-P Effect
The mechanism driving the ejection of jet components from AGN is not settled yet.
Several possibilities have been suggested. Here we propose that the ejection process
could benefit of the existence of a Lagrange internal point (in the static limit of
the Kerr metric) created by the B-P effect at the transition radius. This is a place-
ment wherein a force-free blob of accreted, piled-up material can be readily ejected.
Among possible mechanisms driving the launching of superluminal components one
can quote the instability of the vertical epicyclic oscillation of velocity V31 at radius
r31 , i.e. the 3:1 resonance which can provide energy enough to seed an accretion-
driven outflow from the AGN core. Nonetheless, several other alternative sources of
energy to power the component ejection process are also gravitational. To quote one
of those, one can consider BH-torus systems exhibiting the Aschenbach effect.16 In
such systems, one could benefit of the ∼ 2% reduction in the disk orbital velocity
between radii rmin and rmax around the KBH, which could amount as much as 4.3
MeV/nucleon. However, here we do not discuss further long this issue since it is out
of the scope of this paper.
6. Gravitational Waves from Accretion Disks 487
Back to the mainstream of this section, to describe the emission of GWs during
the early acceleration phase of an ultra relativistic blob of matter ejected from the
AGN core, i.e. piled-up mass that was initially trapped at the transition B-P region,
one can start by linearizing Einstein’s equations (hereafter we follow Ref. 17)
Gµν = −kTµν , (3)
since we expect that the gravitational field produced by the ejection process at
the B-P radius must be weak. To this purpose we use the expansion of the metric
tensor: gµν ηµν +hµν where ηµν defines the Minkowsky metric, and hµν represents
the space-time perturbation produced by the launching of the mass blob. In what
follows we assume that the gµν metric has signature (− + ++), we use Cartesian
coordinates rλ = t, ri with ri = x1 = x, x2 = y, x3 = z, and we also use geometric
units in which G = c = 1, so though k = 8π. We stress in passing that this
GW signal is characterized by a gravitational wave memory, which means that the
amplitude of the GW strain does not go back to zero as far as there is still available
energy for the acceleration phase to go on. The GW signal will remain in that stage
until gravitational energy is available in the radiating source (the launched blob).
¯
Considering the harmonic (Lorenz) gauge hαν ν = 0, one obtains
hµν = hµν β = 16πTµν ,
¯ ¯
β (4)
¯
where hµν = hµν − 1 α
2 ηµν hα .
Notice that one can figure out hereafter the knot as a
“particle” of mass Mb moving along the world line rλ (τ ) (with τ the proper time)
and having an energy-stress tensor
Tµν (x) = Mb Vµ Vν δ (4) [x − r(τ )] dτ, (5)
where V α = drα /dτ is the particle 4-vector velocity.
Plugging this energy source into Eq. (4) leads to the retarded solution (a gener-
alization of the Lienard-Wiechert solution)
¯ Vµ (τ )Vν (τ )
hµν = 4 Mb . (6)
−Vλ · [x − r(τ )]λ
τ =τ0
This result is to be evaluated at the retarded time, which corresponds to the inter-
section time of rα (τ ) with the observer’s past light-cone. Notice that the term in the
denominator, −Vλ · [x − r(τ )]λ , containing the 4-velocity, is responsible for the non
vanishing amplitude (“memory”) of the GW signal emitted during the launching of
the blob from the AGN core.
This metric perturbation when transformed to the Lorenz gauge becomes hµν =
¯ ¯
hµν − 1 ηµν hα ; or equivalently
2 α
4 Mb 1
hµν = Vµ (τ )Vν (τ ) + ηµν . (7)
−Vλ · [x − r(τ )]λ 2
Equation (7) must be furtherly transformed into the transverse - traceless (T T )
gauge, i.e., hµν −→ hT T ; which is the best suited to discuss the GW detector
µν
7. 488 H. J. Mosquera Cuesta et al.
response to that signal. We invite the attentive reader to follow the detailed analysis
of the detector response as given in Ref. 17. Such analysis shows that the maximum
GW strain in the detector is obtained for a wave vector, n, orthogonal to the
detector’s arm. In this case, the GW amplitude then reads
γ Mb β 2 sin2 θ
hmax = , (8)
D 1 − β cos θ
where β = |v|/c, with |v| the particle’s 3-D velocity, θ the angle between v and n,
D the distance to the source and γ the Lorentz expansion factor.
This result, obtained first in Ref. 17, shows that the GW space-time perturbation
is not strongly beamed in the forward direction n, as opposed to the electromagnetic
radiation, for instance in gamma-ray bursts (GRBs). Instead, the metric perturba-
tion at the ultra-relativistic limit (which is the case of superluminal components of
AGN jets, but not for the run away galactic pulsars discussed in Ref. 18) has a direc-
tional dependence which scales as 1 + cos θ. Indeed, because of the strong beaming
effect, the electromagnetic radiation emitted from the source, over the same time
interval, is visible only over the very small solid angle (θ ∼ γ −1 )2 , whereas the GW
signal is observable over a wide solid angle; almost π radians. Besides, the observed
GW frequency is Doppler blueshifted in the forward direction, and therefore the
energy flux carried by the GWs is beamed in the forward direction, too.
Table 1. Physical properties of the C7 component
ejected from quasar 3C 345 for Julian Date 1992.05,
as given in Hirotani et al. (2000).19
N(e− ) Ang. Size Diameter Mass
cm−3 mas pc h−1 M h−3
0.5 - 11 0.20 ± 0.04 0.94 0.66 −→ 1
The two asymptotic forms of the GW amplitude read (always for γ 1)
4 γ Mb β 2 θ2
hmax (θ 1) , (9)
D γ −2 + θ2
2 γ Mb β 2
hmax (θ γ −1 ) (1 + cos θ) . (10)
D
Thus, if one applies this result to the information gathered from the quasar 3C 345
and for its C7 component (see Table 1 and Ref. 9), then the mass of the ejected
component is Mb 1 M . Besides, if one assumes a distance D = 150 Mpc,20
(instead of 2.5 Gpc quoted by earlier references cited by Ref. 9), the angle between
the line-of-sight vs. jet component axis Θl.o.s = 2◦ , the velocity ratio β ∼ 1, and
C7↔
8. Gravitational Waves from Accretion Disks 489
the Lorentz factor γ = 20,14 then one can see that the GW amplitude amounts
h3C 345 Mpc
D=150 1.3 × 10−20 . (11)
This is a GW amplitude which lies within the current strain sensitivity of LISA.b
Meanwhile, because of the invariant compactness of Kerr metric the azimuthal
frequency scales inversely proportional to the KBH mass. That is,
fGW
3C 345
MBH A∗
Sgr
= . (12)
MBH345
3C
fGW
Sgr A∗
In other words, it is consistent with the Rayleigh criterion: in Kerr space-time, the
energy per unit of angular momentum is small at large distances. Nonetheless, the
characteristic acceleration time scale for the vertical launch of a given jet component
during a flare is not properly known. A few AGN have such parameter reasonably
osc
estimated. For instance, Sgr A accretion disk has a period of < ∆Pvert > 500 s for
osc
the vertical oscillations, while the period for the radial oscillations is < ∆Pradial >
60 min. Thus, the rise time for flaring must be either half of, or a few (≤ 0.1) times
the period of vertical oscillations,14,15 while the total duration of a flare must be
a few (≤ 0.1) times the period of radial oscillations. In our studies we associate
this time scale with the interval over which the peak acceleration of (and thus the
maximum amplitude of the associated GW signal from) any ejected component is
reached.
In this respect, since the B-P transition radius can be figured out as a Lagrange
internal point from which each component is force-free ejected, then one can think
of that the characteristic time for such acceleration must be a “universal constant”,
except for some extra factors on the order of 1 (see below the discussion on equipar-
tition of energy between a mass inhomogeneity in the disk and the torus mass).
Indeed, regarding observations of most jets in the whole class of objects under anal-
ysis here, it appears that the distance from the host source that a given jet can
reach does not depend on the mass of the system, but rather on the conditions
in the circumjet medium, as density, for instance. That is, on ideal astrophysical
conditions, all jets might reach the same distance from their host source.c
Thus, based on the Kerr compactness [Eq. (12)], and on the observational fact
that the mass of the pc scale accretion torus in a number of AGN is, in average, les
than a factor of 10 smaller than the mass of the SMBH in their host system, one can
claim that the most likely astrophysical parameter playing some significant role in
a pc scale torus make up by 1 H1 plasma is the sound speed (which involves several
thermodynamical properties). It scales as the square root of the torus density, ρ, and
b Such GW signal would also be detected by Earth-based interferometers, but see next the dis-
cussion on the frequency of this signal.
c One can invoke the Equivalence Principle to assert the existence of a universal time scale, despite
that the KBH in 3C 345 weighs 103 (M ) times more than Sgr A .
9. 490 H. J. Mosquera Cuesta et al.
also dictates the angular frequency of the warps in the disk,21 which hereby fixes
the linear momentum to be delivered to a given jet component during its ejection.
Such parameter depends on both disk height scale and radial size, which in the B-P
effect scenario depends on both the spin parameter and the disk viscosity. (See the
astrophysical foundations of this discussion in Ref. 9.)
Under this premise, one can take the Sgr A flaring time scale as such “universal
constant”. In this way, one can estimate the GW frequency associated to the ejection
of the C7 jet component of 3C 345
1/2
1 1 ρd A∗
= 2 × 10−3 Hz
Sgr
fGW = osc . (13)
< ∆Pvert > 500 s ρd
3C345
This frequency is clearly within the band width of LISA (see Fig. 2). Thus, by
putting the information from both parameters into the strain spectral density dia-
gram of the LISA GW observatory one can claim that the GW signals from accel-
eration of ultra relativistic jet components in this AGN 3C 345 can be detected.
Hence, by extending this result to each process of ejection of components from
AGN; with the characteristic (typical) mass of any ejected component being about
Mb 1 M , one concludes that as far as the rise time (acceleration time scale) is
lower than 105 s, which corresponds to the lowest frequency limit of LISA, such GW
signals would be detectable for distances upto nearly the Hubble radius, i.e. 3 Gpc.
Indeed, to perform a more consistent analysis, or a better characterization, of the
GW signal produced during the early acceleration time of the ejected component,
one can model the growth with time of the GW amplitude through a power-law of
the sort h(t) = h0 (t − t0 )n , where t0 defines the time elapsed till the strain achieves
its “final” steady-state, where no more GW radiation is emitted. In this way, one
,
Fig. 2. Parameter space, fixed by X-ray observations and the compactness of Kerr space-time,
for the GW signals expected from acceleration of jet components in AGN 3C 345, and Sgr A ,
and its potential detectability by current GW observatories.
10. Gravitational Waves from Accretion Disks 491
can evolve the GW waveform (Fourier transform of h(t)) so as to compare it with
the strain-amplitude noise curve of LISA. This analysis will be performed elsewhere
(see the forthcoming paper in Ref. 9).
4. GWs from a Mass Orbiting the SMBH at the Transition Radius
in B-P Dominated AGN
In the case of AGN driven by the B-P effect and suspended accretion any intrinsic
mass-inhomogeneity Mb in the torus, say a lumpiness or blob of mass in a warp
trapped inside the B-P transition region, (which we assume to be eventually ejected
as a jet component), generates a continuous GW signal. The typical strain can be
estimated by using the Peters-Mathews weak field, quadrupole formula,22 which
has been successfully applied to describe the dynamics of the PSR 1913+16 binary
pulsar, and several other similar systems. Hence at the B-P radius a trapped mass
produces a luminosity in GWs given as23
5 5 2 2
MBH 10 Rg Mb 109 M
LGW = 2.5 × 1057 erg s−1 , (14)
109 M RB−P 1M MBH
Mb
where MBH is related to the chirp mass.
In this respect, the observations of the component C7, and the results of our
B-P modeling of 3C 345 shown in Fig. 1, together with the observational parameters
given in Table 1, lead to infer that Mb ∼ 0.66 M . Hereafter, we approximate this
mass inhomogeneity to 1 M in the computations below.
Thus, from this estimate and by recalling the relation between the GW ampli-
tude h and the GW luminosity LGW one can compute the average (modulated)
Fig. 3. Frequency-modulated waveform of the GW signal from accretion disks dominated by B-P
effect.
11. 492 H. J. Mosquera Cuesta et al.
amplitude of each of the GW polarization modes h+ and hx , which then reads9,10
< h+ >
max 6 × 10−22 and < h+ >
min 2 × 10−22 (15)
and
< hx >
max 4 × 10−22 and < hx >
min 2 × 10−22 , (16)
which were obtained for a distance D = 2.45 Gpc to quasar 3C 345. Meanwhile,
for the most quoted distance to 3C 345, D = 150 Mpc, the amplitudes given above
should be multiplied by a factor of 16.7. Be aware of, that in order to search for
this type of signals LISA should integrate it over several periods, which in the case
of 3C 345 amounts to several years.
By analyzing the amplitudes of these strains one can conclude that such GW
signals (see Fig.3) are broad-band and frequency-modulated.9 This feature is due
to the fact that both h+ , hx have the same minimum value of its strain, while the
corresponding maximum strain differs by a factor of 1.5.
Meanwhile, the angular frequency of this GW signal can be computed as the
Keplerian frequency at the Bardeen-Petterson radius, which in Ref. 3 we inferred
to be RB−P = 14Rg , with Rg = GMBH /c2 . In this way, one gets
M 1/2
fGW 3/2
1.25 × 10−7 Hz. (17)
RB−P
Therefore, with these characteristics in the case of 3C 345 such GW signals may not
be detectable by LISA. Nonetheless, the result is quite stimulating since observations
of AGN allow to infer that the masses for SMBHs range between 106 ≤ MBH ≤ 109
M , which means that for SMBHs with masses MBH ≤ 107 M the GW signal from
a typical mass inhomogeneity Mb 1 M orbiting around it, would be detectable
by LISA. As an example, the dynamics around the SMBH in Sgr A would clearly
strike within the amplitude and frequency range of sensitivity (strain-amplitude
noise curve) of the planned LISA space antenna. Certainly, a large sample of other
AGN with similar characteristics as those of Sgr A are relatively close-by to us
(D ≤ 100 Mpc). Thus, their continuous GW signals would be detectable with LISA.
5. Conclusions
From the above analysis one can conclude that any AGN for which the disk and/or
jet precession are driven by the Bardeen-Petterson effect becomes a natural envi-
rons for a suspended accretion state to develop. This B-P effect, in turn, drives
each AGN to become a powerful source of bursts of gravitational waves from the
ultrarelativistic acceleration of jet components, and of continuous broad-line grav-
itational radiation from both the orbiting of blobs of mass at the B-P radius; and
the precession of the distorted, turbulent accretion disk. All such GW signals could
be detected by GW observatories like LISA. One also notices that the prospective
coeval detection of gravitational and electromagnetic radiations from these AGN
12. Gravitational Waves from Accretion Disks 493
may decisively help in picturing a consistent scenario for understanding these cos-
mic sources.
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