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  • richardmitnick 2:53 pm on July 16, 2020 Permalink | Reply
    Tags: "In a first astronomers watch a black hole’s corona disappear then reappear", AGN's - Active galactic nuclei, , , , ,   

    From MIT News: “In a first, astronomers watch a black hole’s corona disappear, then reappear” 

    MIT News

    From MIT News

    July 15, 2020
    Jennifer Chu

    Astronomers at MIT and elsewhere watched a black hole’s corona disappear, then reappear, for first time. A colliding star may have triggered the drastic transformation. Image credit: NASA/JPL-Caltech

    A colliding star may have triggered the drastic transformation.

    It seems the universe has an odd sense of humor. While a crown-encrusted virus has run roughshod over the world, another entirely different corona about 100 million light years from Earth has mysteriously disappeared.

    For the first time, astronomers at MIT and elsewhere have watched as a supermassive black hole’s own corona, the ultrabright, billion-degree ring of high-energy particles that encircles a black hole’s event horizon, was abruptly destroyed.

    The cause of this dramatic transformation is unclear, though the researchers guess that the source of the calamity may have been a star caught in the black hole’s gravitational pull. Like a pebble tossed into a gearbox, the star may have ricocheted through the black hole’s disk of swirling material, causing everything in the vicinity, including the corona’s high-energy particles, to suddenly plummet into the black hole.

    The result, as the astronomers observed, was a precipitous and surprising drop in the black hole’s brightness, by a factor of 10,000, in under just one year.

    “We expect that luminosity changes this big should vary on timescales of many thousands to millions of years,” says Erin Kara, assistant professor of physics at MIT. “But in this object, we saw it change by 10,000 over a year, and it even changed by a factor of 100 in eight hours, which is just totally unheard of and really mind-boggling.”

    Following the corona’s disappearance, astronomers continued to watch as the black hole began to slowly pull together material from its outer edges to reform its swirling accretion disk, which in turn began to spin up high-energy X-rays close to the black hole’s event horizon. In this way, in just a few months, the black hole was able to generate a new corona, almost back to its original luminosity.

    “This seems to be the first time we’ve ever seen a corona first of all disappear, but then also rebuild itself, and we’re watching this in real-time,” Kara says. “This will be really important to understanding how a black hole’s corona is heated and powered in the first place.”

    Kara and her co-authors, including lead author Claudio Ricci of Universidad Diego Portales in Santiago, Chile, have published their findings today in The Astrophysical Journal Letters. Co-authors from MIT include Ron Remillard, and Dheeraj Pasham.

    A nimble washing machine

    In March 2018, an unexpected burst lit up the view of ASSASN, the All-Sky Automated Survey for Super-Novae, that surveys the entire night sky for supernova activity.

    All Sky Automated Survey for Supernovae located at Las Campanas Observatory in Chile, over 2,500 m (8,200 ft) high (since 1997) and the other on Haleakala, Maui (since 2006), Altitude 3,052 m (10,013 ft)

    The survey recorded a flash from 1ES 1927+654, an active galactic nucleus, or AGN, that is a type of supermassive black hole with higher-than-normal brightness at the center of a galaxy. ASSASN observed that the object’s brightness jumped to about 40 times its normal luminosity.

    “This was an AGN that we sort of knew about, but it wasn’t very special,” Kara says. “Then they noticed that this run-of-the-mill AGN became suddenly bright, which got our attention, and we started pointing lots of other telescopes in lots of other wavelengths to look at it.”

    The team used multiple telescopes to observe the black hole in the X-ray, optical, and ultraviolet wave bands. Most of these telescopes were pointed at the the black hole periodically, for example recording observations for an entire day, every six months. The team also watched the black hole daily with NASA’s NICER, a much smaller X-ray telescope, that is installed aboard the International Space Station, with detectors developed and built by researchers at MIT.

    NASA/NICER on the ISS

    “NICER is great because it’s so nimble,” Kara says. “It’s this little washing machine bouncing around the ISS, and it can collect a ton of X-ray photons. Every day, NICER could take a quick little look at this AGN, then go off and do something else.”

    With frequent observations, the researchers were able to catch the black hole as it precipitously dropped in brightness, in virtually all the wave bands they measured, and especially in the high-energy X-ray band — an observation that signaled that the black hole’s corona had completely and suddenly vaporized.

    “After ASSASN saw it go through this huge crazy outburst, we watched as the corona disappeared,” Kara recalls. “It became undetectable, which we have never seen before.”

    A jolting flash

    Physicists are unsure exactly what causes a corona to form, but they believe it has something to do with the configuration of magnetic field lines that run through a black hole’s accretion disk. At the outer regions of a black hole’s swirling disk of material, magnetic field lines are more or less in a straightforward configuration. Closer in, and especially near the event horizon, material circles with more energy, in a way that may cause magnetic field lines to twist and break, then reconnect. This tangle of magnetic energy could spin up particles swirling close to the black hole, to the level of high-energy X-rays, forming the crown-like corona that encircles the black hole.

    Kara and her colleagues believe that if a wayward star was indeed the culprit in the corona’s disappearance, it would have first been shredded apart by the black hole’s gravitational pull, scattering stellar debris across the accretion disk. This may have caused the temporary flash in brightness that ASSASN captured. This “tidal disruption,” as astronomers call such a jolting event, would have triggered much of the material in the disk to suddenly fall into the black hole. It also might have thrown the disk’s magnetic field lines out of whack in a way that it could no longer generate and support a high-energy corona.

    This last point is a potentially important one for understanding how coronas first form. Depending on the mass of a black hole, there is a certain radius within which a star will most certainly be pulled in by a black hole’s gravity.

    “What that tells us is that, if all the action is happening within that tidal disruption radius, that means the magnetic field configuration that’s supporting the corona must be within that radius,” Kara says. “Which means that, for any normal corona, the magnetic fields within that radius are what’s responsible for creating a corona.”

    The researchers calculated that if a star indeed was the cause of the black hole’s missing corona, and if a corona were to form in a supermassive black hole of similar size, it would do so within a radius of about 4 light minutes — a distance that roughly translates to about 75 million kilometers from the black hole’s center.

    “With the caveat that this event happened from a stellar tidal disruption, this would be some of the strictest constraints we have on where the corona must exist,” Kara says.

    The corona has since reformed, lighting up in high-energy X-rays which the team was also able to observe. It’s not as bright as it once was, but the researchers are continuing to monitor it, though less frequently, to see what more this system has in store.

    “We want to keep an eye on it,” Kara says. “It’s still in this unusual high-flux state, and maybe it’ll do something crazy again, so we don’t want to miss that.”

    See the full article here. .

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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 12:26 pm on December 1, 2019 Permalink | Reply
    Tags: "Massive Filaments Fuel the Growth of Galaxies and Supermassive Black Holes", AGN's - Active galactic nuclei, , , , , , SSA22- a massive proto-cluster of galaxies located about 12 billion light years away in the constellation of Aquarius.   

    From National Astronomical Observatory of Japan: “Massive Filaments Fuel the Growth of Galaxies and Supermassive Black Holes” 


    From National Astronomical Observatory of Japan

    October 3, 2019 [Just now in social media]

    An international group of scientists led by the RIKEN Cluster for Pioneering Research has used observations from the Multi Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope (VLT) in Chile and Suprime-Cam at the Subaru Telescope to make detailed observations of the filaments of gas connecting galaxies in a large proto-cluster in the early Universe.

    ESO MUSE on the VLT on Yepun (UT4)

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

    NAOJ Subaru Hyper Suprime-Cam

    Based on direct observations they found that, in accordance with predictions, the filaments are extensive, extending over more than 3 million light years and are providing the fuel for intense formation of stars and the growth of super massive black holes within the proto-cluster.

    It is found that there are extensive gaseous structures and cosmic web filaments (left); and that the filaments connect a number of starbursting galaxies (right). (Credit: RIKEN)
    Figure 1: Maps of gas filaments. For both panels, identified gas filaments are shown in blue color. The background maps are an optical image taken with the Subaru Telescope [below] (left) and a millimeter-wave image taken with ALMA (right).

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    The observations, which constitute a very detailed map of the filaments, were made on SSA22, a massive proto-cluster of galaxies located about 12 billion light years away in the constellation of Aquarius.

    The findings give key insight on the galaxy formation model. Now it is generally believed that filaments in the early universe fueled the formation of galaxies and super massive black holes at places where the filaments crossed, creating dense regions of matter. In accordance with this, the group found that the intersection between the enormous filaments they identified is home to active galactic nuclei—supermassive black holes—and “starbursting” galaxies that have very active star formation. They determined their locations from observations made with the Atacama Large Millimeter/submillimeter Array (ALMA) and the W. M. Keck Observatory.

    Keck Observatory, operated by Caltech and the University of California, Maunakea Hawaii USA, 4,207 m (13,802 ft)

    Their observations are based on the detection using the MUSE instrument of ultraviolet light that is produced by ionized hydrogen gas. The radiation was found to be intense. Their calculations indicated that the high radiation was likely triggered by star-forming galaxies and forming black holes.

    According to Hideki Umehata of the RIKEN Cluster for Pioneering Research and the University of Tokyo, the lead author of the paper, “This suggests very strongly that gas falling along the filaments under the force of gravity triggers the formation of starbursting galaxies and supermassive black holes, giving the universe the structure that we see today.”

    “Previous observations,” he continues, “had shown that there are emissions from blobs of gas extending beyond the galaxies, but now we have been able to clearly show that these filaments are extremely long, going even beyond the edge of the field that we viewed. This adds credence to the idea that these filaments are actually powering the intense activity that we see within the galaxies inside the filaments.”

    Co-author Michele Fumagalli from Durham University, UK, said: “It is very exciting to clearly see for the first time multiple and extended filaments in the early universe. We finally have a way to map these structures directly, and to understand in detail their role in regulating the formation of supermassive black holes and galaxies.”

    The work was done by the RIKEN Cluster for Pioneering Research along with collaborators from the University of Tokyo, Durham University in the UK, National Astronomical Observatory of Japan, Nagoya University, and other institutes.

    These results will be published online on October 3, 2019 in Science (H. Umehata, M. Fumagalli, I. Smail, Y. Matsuda, A. M. Swinbank, S. Cantalupo, C. Sykes, R. J. Ivison, C. C. Steidel, A. E. Shapley, J. Vernet, T. Yamada, Y. Tamura, M. Kubo, K. Nakanishi, M. Kajisawa, B. Hatsukade, and K. Kohno, “Gas filaments of the cosmic web located around active galaxies in a protocluster”). This research is supported by KAKENHI (Numbers JP17K14252, JP25287043, JP17H04831, JP17KK0098, JP19K03925, JP17H06130, JP17H06130) and NAOJ ALMA Scientific Research Grant Number 2018-09B.

    See the full article here .


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    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

  • richardmitnick 2:46 pm on October 2, 2019 Permalink | Reply
    Tags: AGN's - Active galactic nuclei, , The neutrino event IceCube 170922A and the distant BL Lac object active galaxy TXS 0506+056, This was the first neutrino from outer space whose origin could be confirmed.,   

    From Max Planck Institute for Radio Astronomy: “Neutrino produced in a cosmic collider far away” 

    From Max Planck Institute for Radio Astronomy

    October 02, 2019

    Priv.-Doz. Dr. Silke Britzen
    Phone:+49 228 525-280
    Max Planck Institute for Radio Astronomy,Bonn

    Prof. Dr. Christian Fendt
    Phone:+49 6221 528-387
    Max Planck Institute for Radio Astronomy,Heidelberg

    Max-Planck-Institut für Astronomie,
    Dr. Norbert Junkes
    Press and Public Outreach
    Phone:+49 228 525-399
    Max Planck Institute for Radio Astronomy,Bonn

    Link between IceCube neutrino event and distant radio galaxy resolved

    The neutrino event IceCube 170922A, detected at the IceCube Neutrino Observatory at the South Pole, appears to originate from the distant active galaxy TXS 0506+056, at a light travel distance of 3.8 billion light years. TXS 0506+056 is one of many active galaxies and it remained a mystery, why and how only this particular galaxy generated neutrinos so far.

    An international team of researchers led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, studied high-resolution radio observations of the source between 2009 and 2018, before and after the neutrino event. The team proposes that the enhanced neutrino activity during an earlier neutrino flare and the single neutrino could have been generated by a cosmic collision within TXS 0506+056. The clash of jet material close to a supermassive black hole seems to have produced the neutrinos.

    The results are published in Astronomy & Astrophysics, October 02, 2019.

    TXS 0506+056. The neutrino event IceCube 170922A appears to originate in the interaction zone of the two jets.
    © IceCube Collaboration, MOJAVE, S. Britzen, & M. Zajaček

    On July 12, 2018, the IceCube collaboration announced the detection of the first high-energy neutrino, IceCube-170922A, which could be traced back to a distant cosmic origin. While the cosmic origin of neutrinos had been suspected for quite some time, this was the first neutrino from outer space whose origin could be confirmed. The “home” of this neutrino is an Active Galactic Nucleus (AGN) – a galaxy with a supermassive black hole as central engine. An international team could now clarify the production mechanism of the neutrino and found an equivalent to a collider on Earth: a cosmic collision of jetted material.

    AGN are the most energetic objects in our Universe. Powered by a supermassive black hole, matter is being accreted and streams of plasma (so-called jets) are launched into intergalactic space. BL Lac objects form a special class of these AGN, where the jet is directly pointing at us and dominating the observed radiation. The neutrino event IceCube-170922A appears to originate from the BL Lac object TXS 0506+056, a galaxy at a redshift of z=0.34, corresponding to a light travel distance of 3.8 billion light years. An analysis of archival IceCube data by the IceCube Collaboration had revealed evidence of an enhanced neutrino acitvity earlier, between September 2014 and March 2015.

    Other BL Lac Objects show properties quite similar to those of TXS 0506+056. „It was a bit of a mystery, however, why only TXS 0506+056 has been identified as neutrino emitter“, explains Silke Britzen from the Max Planck Institute for Radio Astronomy (MPIfR), the lead author of the paper. „We wanted to unravel what makes TXS 0506+056 special, to understand the neutrino creation process and to localize the emission site and studied a series of high resolution radio images of the jet.“

    Much to their surprise, the researchers found an unexpected interaction between jet material in TXS 0506+056. While jet plasma is usually assumed to flow undisturbed in a kind of channel, the situation seems different in TXS 0506+056. The team proposes that the enhanced neutrino activity during the neutrino flare in 2014–2015 and the single EHE neutrino
    IceCube-170922A could have been generated by a cosmic collision within the source.

    This cosmic collision can be explained by new jet material clashing into older jet material. A strongly curved jet structure provides the proper set up for such a scenario. Another explanation involves the collision of two jets in the same source. In both scenarios, it is the collision of jetted material which generates the neutrino. Markus Böttcher from the North-West University in Potchefstroom (South Africa), a co-author of the paper, performed the calculations with regard to the radiation and particle emission. „This collision of jetted material is currently the only viable mechanism which can explain the neutrino detection from this source. It also provides us with important insight into the jet material and solves a long-standing question whether jets are leptonic, consisting of electrons and positrons, or hadronic, consisting of electrons and protons, or a combination of both. At least part of the jet material has to be hadronic – otherwise, we would not have detected the neutrino.“

    In the course of the cosmic evolution of our Universe, collisions of galaxies seem to be a frequent phenomenon. Assuming that both galaxies contain central supermassive black holes, the galactic collision can result in a black hole pair at the centre. This black hole pair might eventually merge and produce the supermassive equivalent to stellar black hole mergers as detected in gravitational waves by the LIGO/Virgo collaboration.

    AGN with double black holes at a small separation of only light years have been pursued for many years. However, they seem to be rare and difficult to identify. In addition to the collision of jetted material, the team also found evidence for a precession of the central jet of TXS 0506+056. According to Michal Zajaček from the Center for Theoretical Physics, Warsaw: „This precession can in general be explained by the presence of a supermassive black hole binary or the Lense-Thirring precession effect as predicted by Einstein’s theory of general relativity. The latter could also be triggered by a second, more distant black hole in the centre. Both scenarios lead to a wandering of the jet direction, which we observe.“

    Christian Fendt from the Max Planck Institute for Astronomy in Heidelberg is amazed: „The closer we look at the jet sources the more complicated the internal structure and jet dynamics appears. While binary black holes produce a more complex outflow structure, their existence is naturally expected from the cosmological models of galaxy formation by galaxy mergers.”

    Silke Britzen stresses the scientific potential of the findings: „It’s fantastic to understand the neutrino generation by studying the insides of jets. And it would be a breakthrough if our analysis had provided another candidate for a binary black hole jet source with two jets.“

    It seems to be the first time that a potential collision of two jets on scales of a few light years has been reported and that the detection of a cosmic neutrino might be traced back to a cosmic jet-collision.

    While TXS 0506+056 might not be representative of the class of BL Lac objects, this source could provide the proper setup for a repeated interaction of jetted material and the generation of neutrinos.

    Background Information:

    U Wisconsin ICECUBE neutrino detector at the South Pole

    The IceCube Neutrino Observatory is designed to observe the cosmos from deep within the South Pole ice.

    IceCube is a particle detector at the South Pole that records the interactions of a nearly massless sub-atomic particle called the neutrino. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma ray bursts, and cataclysmic phenomena involving black holes and neutron stars. The IceCube telescope is a powerful tool to search for dark matter, and could reveal the new physical processes associated with the enigmatic origin of the highest energy particles in nature. In addition, exploring the background of neutrinos produced in the atmosphere, IceCube studies the neutrinos themselves; their energies far exceed those produced by accelerator beams. IceCube is the world’s largest neutrino detector, encompassing a cubic kilometer of ice.

    IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration

    Lunar Icecube

    IceCube DeepCore annotated

    IceCube PINGU annotated

    DM-Ice II at IceCube annotated

    Encompassing a cubic kilometer of ice, IceCube searches for nearly massless subatomic particles called neutrinos. These high-energy astronomical messengers provide information to probe the most violent astrophysical sources: events like exploding stars, gamma-ray bursts, and cataclysmic phenomena involving black holes and neutron stars.

    MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) is a long-term program to monitor radio brightness and polarization variations in jets associated with active galaxies visible in the northern sky. The Very Long Baseline Array (VLBA) is a system of ten radio telescopes which are operated from Socorro, New Mexico. The ten radio antennas work together as an array using very long baseline interferometry.


    A BL Lac Object is a special subclass of an Active Galactic Nucleus (AGN). An AGN is a compact region at the center of a galaxy that has a much higher than normal luminosity over at least some portion of the electromagnetic spectrum. This luminosity is non-thermal and produced by accretion of matter close to a central black hole. The jet of a BL Lac Object is directed at the observer giving a unique radio emission spectrum.

    Authors of the original paper in “Astronomy & Astrophysics” are Silke Britzen, Christian Fendt, Markus Böttcher, Michal Zajaček, Frederic Jaron, Ilya Pashchenko, Anabella Araudo, Vladimir Karas, and Omar Kurtanidze. Silke Britzen, the first author, and also Michal Zajaček and Frederic Jaron are affiliated to the MPIfR.

    Besides MPIfR, affiliations of the authors include the Max-Planck-Institut für Astronomie (Heidelberg, Germany), the Centre for Space Research (North-West University, Potchefstroom, South Africa), the I. Physikalisches Institut, (Universität Köln, Germany), the Center for Theoretical Physics, (Polish Academy of Sciences, Warsaw, Poland), the Institute of Geodesy and Geoinformation (University of Bonn, Germany), the Astro Space Center, (Lebedev Physical Institute, Russian Academy of Sciences, Russia), the Astronomical Institute and the Institute of Physics (Czech Academy of Sciences, Prague, Czech Republic) and the Abastumani Observatory in Georgia.

    See the full article here .


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    MPIFR/Effelsberg Radio Telescope, Germany

    The Max Planck Institute for Radio Astronomy (German: Max-Planck-Institut für Radioastronomie) is located in Bonn, Germany. It is one of 80 institutes in the Max Planck Society (German: Max-Planck-Gesellschaft).

    By combining the already existing radio astronomy faculty of the University of Bonn led by Otto Hachenberg with the new Max Planck institute the Max Planck Institute for Radio Astronomy was formed. In 1972 the 100-m radio telescope in Effelsberg was opened. The institute building was enlarged in 1983 and 2002.

    The institute was founded in 1966 by the Max-Planck-Gesellschaft as the “Max-Planck-Institut für Radioastronomie” (MPIfR).

    The foundation of the institute was closely linked to plans in the German astronomical community to construct a competitive large radio telescope in (then) West Germany. In 1964, Professors Friedrich Becker, Wolfgang Priester and Otto Hachenberg of the Astronomische Institute der Universität Bonn submitted a proposal to the Stiftung Volkswagenwerk for the construction of a large fully steerable radio telescope.

    In the same year the Stiftung Volkswagenwerk approved the funding of the telescope project but with the condition that an organization should be found, which would guarantee the operations. It was clear that the operation of such a large instrument was well beyond the possibilities of a single university institute.

    Already in 1965 the Max-Planck-Gesellschaft (MPG) decided in principle to found the Max-Planck-Institut für Radioastronomie. Eventually, after a series of discussions, the institute was officially founded in 1966.

    The Max Planck Society for the Advancement of Science (German: Max-Planck-Gesellschaft zur Förderung der Wissenschaften e. V.; abbreviated MPG) is a formally independent non-governmental and non-profit association of German research institutes founded in 1911 as the Kaiser Wilhelm Society and renamed the Max Planck Society in 1948 in honor of its former president, theoretical physicist Max Planck. The society is funded by the federal and state governments of Germany as well as other sources.

    According to its primary goal, the Max Planck Society supports fundamental research in the natural, life and social sciences, the arts and humanities in its 83 (as of January 2014)[2] Max Planck Institutes. The society has a total staff of approximately 17,000 permanent employees, including 5,470 scientists, plus around 4,600 non-tenured scientists and guests. Society budget for 2015 was about €1.7 billion.

    The Max Planck Institutes focus on excellence in research. The Max Planck Society has a world-leading reputation as a science and technology research organization, with 33 Nobel Prizes awarded to their scientists, and is generally regarded as the foremost basic research organization in Europe and the world. In 2013, the Nature Publishing Index placed the Max Planck institutes fifth worldwide in terms of research published in Nature journals (after Harvard, MIT, Stanford and the US NIH). In terms of total research volume (unweighted by citations or impact), the Max Planck Society is only outranked by the Chinese Academy of Sciences, the Russian Academy of Sciences and Harvard University. The Thomson Reuters-Science Watch website placed the Max Planck Society as the second leading research organization worldwide following Harvard University, in terms of the impact of the produced research over science fields.

  • richardmitnick 11:50 am on March 19, 2019 Permalink | Reply
    Tags: , AGN's - Active galactic nuclei, , , “Missing Gamma-Ray Halos and the Need for New Physics in the Gamma-Ray Sky”, , , High-energy gamma-ray photons,   

    From AAS NOVA: ” Missing Halos in the High-Energy Sky” 


    From AAS NOVA

    18 March 2019
    Susanna Kohler

    This composite image reveals Centaurus A, a galaxy with an active nucleus spewing fast-moving jets into its surroundings. Active galactic nuclei like this one produce extremely high-energy photons. [ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray)]

    Wide Field Imager on the 2.2 meter MPG/ESO telescope at Cerro LaSilla

    MPG/ESO 2.2 meter telescope at Cerro La Silla, Chile, 600 km north of Santiago de Chile at an altitude of 2400 metres

    ESO/MPIfR APEX high on the Chajnantor plateau in Chile’s Atacama region, at an altitude of over 4,800 m (15,700 ft)

    NASA/Chandra X-ray Telescope

    What’s going on in our high-energy sky? Powerful phenomena abound in our universe, and they can produce photons with tremendous energies. A new study explores a high-energy mystery from one of these sources: active galactic nuclei, or AGN.

    Gamma rays span a broad range of energies in the most energetic part of the electromagnetic spectrum. Very high-energy gamma rays initially emitted from AGN have energies above 100 GeV, but these are reprocessed by interactions with background photons to energies of 1–100 GeV. [Ulflund]

    Where Are the Gamma Rays?

    Active galactic nuclei — the accreting supermassive black holes lurking at the centers of some galaxies — dot our universal landscape, spewing out very high-energy gamma-ray photons within jets moving at nearly the speed of light. These energetic photons speed across the sky — but they don’t travel unencumbered.

    Theory predicts that this energetic emission should be effectively reprocessed as it slams into the cosmic microwave background, generating a compact sheath of gamma-ray emission in the 1–100 GeV range, beamed forward in the direction of the jets emitted from each AGN. But there’s a problem: we don’t see this expected flux.

    Galactic coordinates of the sources used to generate the authors’ stacked analysis. Two types of AGN-containing galaxies are included: FR I and FR II galaxies. [Broderick et al. 2019]

    One possible explanation for the missing light is that these traveling photons could be deflected from their path by a strong, large-scale magnetic field threading through intergalactic space. This would convert the compact, forward-beamed sheath into a more diffuse, harder-to-spot gamma-ray halo around each AGN. In a new study, a team of scientists led by Avery Broderick (University of Waterloo and the Perimeter Institute for Theoretical Physics, Canada) has gone on the hunt for these missing gamma-ray halos.

    Perimeter Institute in Waterloo, Canada

    Stacks of Galaxies

    Though the proposed gamma-ray halos may be too faint to spot individually, Broderick and collaborators suggest that by stacking a bunch of gamma-ray observations of off-axis AGN on top of one another, we should easily be able to detect their combined halo — if it exists.

    The process of aligning the jets in two different radio images: an FR I galaxy (top) and an FR II galaxy (bottom). [Broderick et al. 2019]

    To do this, the AGN must first be oriented in the same direction. Broderick and collaborators use radio observations of AGN jets pointed off our line of sight to identify each jet’s orientation. They determine the transformations needed to align each of the radio jets, and then apply this transformation to corresponding Fermi-telescope gamma-ray observations of the active galaxies. The result is a sample of nearly 9,000 gamma-ray observations of AGN, all oriented in the same direction.

    Broderick and collaborators then stack these observations and compare their results to a model of what we would expect to see if an intergalactic magnetic field were deflecting the gamma-ray photons, generating a faint halo around the AGN.

    Still No Halos

    Top: the authors’ stacked gamma-ray observations for FR I (left) and FR II (right) galaxies. Bottom: the expected signals if gamma-ray halos were present. The observations clearly rule out the presence of faint halos. [Broderick et al. 2019]

    Intriguingly, the authors find no hint of a combined gamma-ray halo. Their non-detection places strict limits on the strength of the intergalactic magnetic field allowed in this picture, and it rules out magnetic fields as an explanation for why we don’t see the gamma rays we expect from AGN.

    What does this mean? Broderick and collaborators argue that this requires us to consider brand new physics in high-energy processes. There must be some unexpected mechanism that prevents the creation of the expected gamma-ray halos, either because the highest-energy emission is suppressed in gamma-ray bright AGN, or because some process affects this emission before it can lead to the generation of halos. The mystery deepens!


    “Missing Gamma-Ray Halos and the Need for New Physics in the Gamma-Ray Sky,” Avery E. Broderick et al 2018 ApJ 868 87.

    See the full article here .


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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

  • richardmitnick 5:15 pm on September 8, 2018 Permalink | Reply
    Tags: AGN's - Active galactic nuclei, , QUEST-La Silla AGN Variability Survey, ,   

    From Discover Magazine: “Black Holes Flicker as They Stop Gorging Themselves on Matter” 


    From Discover Magazine

    September 7, 2018
    Alison Klesman

    This artistically enhanced image shows a Hubble Space Telescope view of the active galaxy Arp 220, which houses a feeding supermassive black hole at its center. (Credit: NASA/JPL-Caltech)

    NASA/ESA Hubble Telescope

    Black holes are by nature difficult to study directly. Because even light cannot escape these massive objects, astronomers must turn to other methods to spot and study them. While information is lost once it crosses a black hole’s event horizon, outside that boundary, it can still escape. A recent study, led by a graduate student in the Department of Astronomy of the Universidad de Chile, has now found that the amount of light emitted from around a black hole is determined by one thing, and one thing only: the rate at which matter is falling into the black hole.

    The research, published September 4 in The Astrophysical Journal, was aimed at determining the physical mechanism behind the variability observed from the active black holes at the centers of galaxies (known as active galactic nuclei, or AGN), which are supermassive black holes currently sucking in matter.

    In astronomy, this process is known as accretion. Such black holes have accretion disks, which are disks of matter swirling around them as it is funneled inward, like water going down a drain. Outside the event horizon, these disks shine brightly as the material inside is heated by friction, giving off visible light and even more energetic light, such as X-rays. These disks are also variable — astronomers aren’t exactly sure why, but the current understanding is that as clumps of matter interact in the disk or fall into the black hole, it causes changes in the light the disk emits.

    The team combined data from the Sloan Digital Sky Survey and the QUEST-La Silla AGN Variability Survey to combine physical properties —the mass and the accretion rate, or the speed at which a black hole is eating — of about 2,000 AGN with information about their variability.

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    ESO/Cerro LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    What they found was surprising: “Contrary to what was believed, the only important physical property to explain the amplitude of the variability is the AGN accretion rate,” said Paula Sánchez-Sáez, the student who led the study and first author of the paper, in a press release.

    Out With The Old

    Why is this surprising? “The results obtained in this study challenge the old paradigm that the amplitude of the AGN variability depended mainly on the luminosity of the AGN,” Sánchez-Sáez said. What this means is that previously, astronomers assumed that more luminous (brighter) AGN varied more, while less luminous (dimmer) AGN varied less. This study instead discovered that the rate at which a black hole is eating is the only thing that affects the amount its light varies, regardless of whether it is bright or dim.

    But the challenge to previous thinking makes sense, Sánchez-Sáez said, because in the past, it’s been difficult to accurately measure a black hole’s mass, and thus its accretion rate. Only with newer data provided by large surveys can astronomers begin to build up the numbers they need to test their assumptions.

    With Black Holes, Less is More

    Furthermore, the study revealed a relationship that may seem backwards: “What we detect is that the less they [black holes] swallow, the more they vary,” said Paulina Lira of the Universidad de Chile and the CATA Center for Excellence in Astrophysics, and a co-author on the paper. In scientific terms, the amplitude (amount) of variability is inversely proportional to the accretion rate, or the amount of food a black hole is consuming at any given time.

    This initial study was based on variability information from the QUEST-La Silla AGN Variability Survey spanning about five years. Now, the researchers are looking to study the variability of these objects in greater detail, for which they’ll need more data. That means staring at these AGN for longer periods of time — at least 10 years or more. For that, they’ll need to wait for future surveys, such as those proposed with the Large Synoptic Survey Telescope, which is expected to reach full science operations by 2023. This will “extend our light curves to an order of 20 years,” said Lira, providing an even more accurate picture of the black hole’s behavior over longer periods of time.

    See the full article here .


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  • richardmitnick 2:42 pm on April 28, 2018 Permalink | Reply
    Tags: AGN's - Active galactic nuclei, , , , ,   

    From Center For Astrophysics: “Finding Galaxies with Active Nuclei” 

    Harvard Smithsonian Center for Astrophysics

    Center For Astrophysics

    The Hubble image of a galaxy spotted by Spitzer’s IRAC infrared camera to be variable, probably because it harbors an active galactic nucleus. IRAC infrared surveys taken over a decade have spotted about 800 previously unknown AGN. NASA/Hubble; Polimera et al. 2018

    The nuclei of most galaxies host supermassive black holes with millions or even billions of solar-masses of material. Material in the vicinity of such black holes can accrete onto a torus of dust and gas around the black hole, and when that happens the nuclei radiate powerfully across the full spectrum. These active galactic nuclei (AGN) are among the most dramatic and interesting phenomena in extragalactic astronomy, and puzzling as well.

    Inner Structure of an Active Galaxy. 8 February 2016. Author Original: Unknown; Vectorization: Wikipedia user-Rothwild

    Exactly what turns the accretion on or off is not understood, nor is how the associated processes produce the emission, generate jets of particles, or influence star formation in the galaxy.

    Because AGN play an important role in the evolution of galaxies, astronomers are studying galaxies with AGN at cosmological distances. It is in earlier epochs of the universe, about ten billion years after the big bang, when the most significant AGN fueling is thought to occur. But AGN at these distances are also faint and more difficult to find. Historically, they have been spotted by their having very red colors due to heavy dust obscuration, characteristic emission lines (signaling very hot gas), and/or their variability.

    CfA astronomers Matt Ashby, Steve Willner and Giovanni Fazio and two colleagues used deep infrared extragalactic surveys taken over 14 years by the IRAC instrument on the Spitzer Space Telescope to search for distant AGN. The various surveys in the archive repeatedly scanned different portions of the sky over as many as eleven epochs in their efforts to peer deeper and farther into the cosmos, and the multiple observations allow spotting variable sources. The astronomers found almost a thousand infrared-variable galaxies in these surveys, about one percent of all the galaxies recorded. They estimate that about eighty percent of these variable sources are AGN, the others being due either to supernovae or spurious data. The variability had not been seen in studies at other wavelengths because of the heavy obscuration around the nuclei and/or the weakness of X-ray emission; the infrared can peer through the obscuring dust. The team examined Hubble images of the sources and finds that a majority show indication of disruption, perhaps from a galaxy-galaxy collision. Their results suggest that mid-infrared variability identifies a unique population of galaxies with AGN.

    Science paper:
    Morphologies of mid-IR variability-selected AGN host galaxies . MNRAS

    See the full article here .

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

  • richardmitnick 9:02 am on February 14, 2018 Permalink | Reply
    Tags: AGN's - Active galactic nuclei, , , , , , , ,   

    From ALMA: “ALMA Observes a Rotating Dust and Gas Donut around a Supermassive Black Hole” 

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres


    14 February, 2018

    Nicolás Lira
    Education and Public Outreach Coordinator
    Joint ALMA Observatory, Santiago – Chile
    Phone: +56 2 2467 6519
    Cell phone: +56 9 9445 7726
    Email: nicolas.lira@alma.cl

    Masaaki Hiramatsu
    Education and Public Outreach Officer, NAOJ Chile
, Tokyo – Japan
    Phone: +81 422 34 3630
    Email: hiramatsu.masaaki@nao.ac.jp

    Charles E. Blue
    Public Information Officer
    National Radio Astronomy Observatory Charlottesville, Virginia – USA
    Phone: +1 434 296 0314
    Cell phone: +1 202 236 6324
    Email: cblue@nrao.edu

    Richard Hook
    Public Information Officer, ESO
    Garching bei München, Germany
    Phone: +49 89 3200 6655
    Cell phone: +49 151 1537 3591
    Email: rhook@eso.org

    Artist’s impression of the dusty gaseous torus around an active supermassive black hole. ALMA revealed the rotation of the torus very clearly for the first time. Credit: ALMA (ESO/NAOJ/NRAO)

    High resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) imaged a rotating dusty gas torus around an active supermassive black hole. The existence of such rotating donuts-shape structures was first suggested decades ago, but this is the first time one has been confirmed so clearly. This is an important step in understanding the co-evolution of supermassive black holes and their host galaxies.

    The central region of the spiral galaxy M77. The NASA/ESA Hubble Space Telescope imaged the distribution of stars. ALMA revealed the distribution of gas in the very center of the galaxy. ALMA imaged a horseshoe-like structure with a radius of 700 light-years and a central compact component with a radius of 20 light-years. The latter is the gaseous torus around the AGN. Red indicates emission from formyl ions (HCO+) and green indicates hydrogen cyanide emission. Credit: ALMA (ESO/NAOJ/NRAO), Imanishi et al., NASA/ESA Hubble Space Telescope and A. van der Hoeven

    NASA/ESA Hubble Telescope

    Almost all galaxies hold concealed monstrous black holes in their centers. Researchers have known for a long time that the more massive the galaxy is, the more massive the central black hole is. This sounds reasonable at first, but host galaxies are 10 billion times bigger than the central black holes; it should be difficult for two objects of such vastly different scales to directly affect each other. So how could such a relation develop?

    Aiming to solve this shadowy problem, a team of astronomers utilized the high resolution of ALMA to observe the center of spiral galaxy M77. The central region of M77 is an “active galactic nucleus,” or AGN, which means that matter is vigorously falling toward the central supermassive black hole and emitting intense light. AGNs can strongly affect the surrounding environment, therefore they are important objects for solving the mystery of the co-evolution of galaxies and black holes.

    The team imaged the area around the supermassive black hole in M77 and resolved a compact gaseous structure with a radius of 20 light-years. And, the astronomers found that the compact structure is rotating around the black hole, as expected.2
    Motion of gas around the supermassive black hole in the center of M77. The gas moving toward us is shown in blue and that moving away from us is in red. The gas’s rotation is centered around the black hole. Credit: ALMA (ESO/NAOJ/NRAO), Imanishi et al.

    “To interpret various observational features of AGNs, astronomers have assumed rotating donut-like structures of dusty gas around active supermassive black holes. This is called the ‘unified model’ of AGN,” explained Masatoshi Imanishi, from the National Astronomical Observatory of Japan (NAOJ), the lead author on a paper published in the Astrophysical Journal Letters. “However, the dusty gaseous donut is very tiny in appearance. With the high resolution of ALMA, now we can directly see the structure.”

    Many astronomers have observed the center of M77 before, but never has the rotation of the gas donut around the black hole been seen so clearly. Besides the superior resolution of ALMA, the selection of molecular emission lines to observe was key to revealing the structure. The team observed specific microwave emission from hydrogen cyanide molecules (HCN) and formyl ions (HCO+). These molecules emit microwaves only in dense gas, whereas the more frequently observed carbon monoxide (CO) emits microwaves under a variety of conditions [1]. The torus around the AGN is assumed to be very dense, and the team’s strategy was right on the mark.

    “Previous observations have revealed the east-west elongation of the dusty gaseous torus. The dynamics revealed from our ALMA data agrees exactly with the expected rotational orientation of the torus,” said Imanishi.

    Interestingly, the distribution of gas around the supermassive black hole is much more complicated than what a simple unified model suggests. The torus seems to have an asymmetry and the rotation is not just following the gravity of the black hole but also contains highly random motion. These facts could indicate the AGN had a violent history, possibly including a merger with a small galaxy [2]. Nevertheless, the identification of the rotating torus is an important step.

    The Milky Way Galaxy, where we live, also has a supermassive black hole at its center.

    Milky Way Galaxy Credits: NASA/JPL-Caltech/R. Hurt

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    This black hole is, however, in a very quiet state. Only a tiny amount of gas is accreting onto it. Therefore, to investigate an AGN in detail, astronomers need to observe the centers of distant galaxies. M77 is one of the nearest AGN and a suitable object for peering into the very center in detail.

    These observation results were published as Imanishi et al. ALMA Reveals an Inhomogeneous Compact Rotating Dense Molecular Torus at the NGC 1068 Nucleus in the Astrophysical Journal Letters (2018 February 1 issue, 853, L25).

    The research team members are:

    Masatoshi Imanishi (National Astronomical Observatory of Japan/SOKENDAI), Kouichiro Nakanishi (National Astronomical Observatory of Japan/SOKENDAI), Takuma Izumi (National Astronomical Observatory of Japan), and Keiichi Wada (Kagoshima University).


    [1] García-Burillo et al. (2016) observed the distribution and motion of CO with ALMA and did not find clear rotation along the east-west torus direction. Their interpretation is that the turbulent motion is so intense that the east-west oriented rotating motion is not clear. Gallimore et al. (2016) also observed CO emission and found gas motion in the north-south direction. They interpret this as outflowing gas from the black hole.

    [2] Recently, astronomers used the Subaru Telescope to observe M77 and revealed signatures of a merger with a small galaxy billions of years ago. For details, please read the press release Minor Merger Kicks Supermassive Black Hole into High Gear issued in October 2017 from the Subaru Telescope.

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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  • richardmitnick 8:45 am on February 8, 2018 Permalink | Reply
    Tags: A New Look at Speeding Outflows, , AGN's - Active galactic nuclei, , , , , , UFOs- ultra-fast outflows   

    From AAS NOVA: ” A New Look at Speeding Outflows” 



    7 February 2018
    Susanna Kohler

    Artist’s impression of a galaxy that is releasing material via two strongly collimated jets (shown in red/orange) as well as via wide-angle, ultra-fast outflows (shown in gray/blue). The inset shows a closeup of the accretion disk and central supermassive black hole at the galaxy’s core. [ESA/AOES Medialab].

    The compact centers of active galaxies — known as active galactic nuclei, or AGN — are known for the dynamic behavior they exhibit as the supermassive black holes at their centers accrete matter. New observations of outflows from a nearby AGN provide a more detailed look at what happens in these extreme environments.

    Outflows from Giants

    The powerful radio jets of Cygnus A, which extend far beyond the galaxy. [NRAO/AUI].

    AGN consist of a supermassive black hole of millions to tens of billions of solar masses surrounded by an accretion disk of in-falling matter. But not all the material falling toward the black hole accretes! Some of it is flung from the AGN via various types of outflows.

    The most well-known of these outflows are powerful radio jets — collimated and incredibly fast-moving streams of particles that blast their way out of the host galaxy and into space. Only around 10% of AGN are observed to host such jets, however — and there’s another outflow that’s more ubiquitous.

    Fast-Moving Absorbers

    Perhaps 30% of AGN — both those with and without observed radio jets — host wider-angle, highly ionized gaseous outflows known as ultra-fast outflows (UFOs). Ultraviolet and X-ray radiation emitted from the AGN is absorbed by the UFO, revealing the outflow’s presence: absorption lines appear in the ultraviolet and X-ray spectra of the AGN, blue-shifted due to the high speeds of the absorbing gas in the outflow.

    Quasar PG 1211+143, indicated by the crosshairs at the center of the image, in the color context of its surroundings. [SDSS/S. Karge]

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    But what is the nature of UFOs? Are they disk winds? Or are they somehow related to the radio jets? And what impact do they have on the AGN’s host galaxy?

    X-ray and Ultraviolet Cooperation

    New observations are now providing fresh information about one particular UFO. A team of scientists led by Ashkbiz Danehkar (Harvard-Smithsonian Center for Astrophysics [CfA]) recently used the Chandra and Hubble space telescopes to make the first simultaneous observations of the same outflow — a UFO in quasar PG 1211+143 — in both X-rays and in ultraviolet.

    Danehkar and collaborators found absorption lines in both sets of data revealing an outflow moving at ~17,000 km/s (for reference, that’s ~5.6% of the speed of light, and more than 1,500 times faster than Elon Musk’s roadster will be traveling at its maximum speed in the orbit it was launched onto yesterday by the Falcon Heavy). Having the information both from the X-ray and the ultraviolet data provides the opportunity to better asses the UFO’s physical characteristics.

    A Link Between Black Holes and Galaxies?

    The X-ray spectrum for PG 1211+143 was obtained by Chandra HETGS (top); the ultraviolet spectrum was obtained by HST-COS G130M (bottom). [Adapted from Danehkar et al. 2018]

    NASA/Chandra Telescope

    NASA/ESA Hubble Telescope

    The authors use models of the data to demonstrate the plausibility of a scenario in which a shock driven by the radio jet gives rise to the fast bulk outflows detected in the X-ray and ultraviolet spectra.

    They also estimate the impact that the outflows might have on the AGN’s host galaxy, demonstrating that the energy injected into the galaxy could be somewhere between 0.02% and 0.6% of the AGN’s total luminosity. At the higher end of this range, this could have an evolutionary impact on the host galaxy, suggesting a possible link between the black hole’s behavior and how its host galaxy evolves.

    In order to draw definitive conclusions, we will need higher-resolution observations that can determine the total size and extent of these outflows. For that, we may need to wait for 2023, when a proposed X-ray spectrometer that might fit the bill, Arcus, may be launched.


    Ashkbiz Danehkar et al 2018 ApJ http://iopscience.iop.org/article/10.3847/1538-4357/aaa427/meta

    See the full article here .

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    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

  • richardmitnick 5:09 pm on December 26, 2017 Permalink | Reply
    Tags: 'Direct Collapse' Black Holes May Explain Our Universe's Mysterious Quasars, AGN's - Active galactic nuclei, , , , , , , , , Star formation is a violent process, ,   

    From Ethan Siegel: “‘Direct Collapse’ Black Holes May Explain Our Universe’s Mysterious Quasars” 

    From Ethan Siegel
    Dec 26, 2017

    The most distant X-ray jet in the Universe, from quasar GB 1428, is approximately the same distance and age, as viewed from Earth, as quasar S5 0014+81; both are over 12 billion light years away. X-ray: NASA/CXC/NRC/C.Cheung et al; Optical: NASA/STScI; Radio: NSF/NRAO/VLA

    NASA/Chandra Telescope

    NASA/ESA Hubble Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    There’s a big problem when we look at the brightest, most energetic objects we can see in the early stages of the Universe. Shortly after the first stars and galaxies form, we find the first quasars: extremely luminous sources of radiation that span the electromagnetic spectrum, from radio up through the X-ray. Only a supermassive black hole could possibly serve as the engine for one of these cosmic behemoths, and the study of active objects like quasars, blazars, and AGNs all support this idea. But there’s a problem: it may not be possible to make a black hole so large, so quickly, to explain these young quasars that we see. Unless, that is, there’s a new way to make black holes beyond what we previously thought. This year, we found the first evidence for a direct collapse black hole, and it may lead to the solution we’ve sought for so long.

    While distant host galaxies for quasars and active galactic nuclei can often be imaged in visible/infrared light, the jets themselves and the surrounding emission is best viewed in both the X-ray and the radio, as illustrated here for the galaxy Hercules A. It takes a black hole to power an engine such as this. NASA, ESA, S. Baum and C. O’Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA).

    Generically known as ‘active galaxies,’ almost all galaxies posses supermassive black holes at their center, but only a few emit the intense radiation associated with quasars or AGNs. The leading idea is that supermassive black holes will feed on matter, accelerating and heating it, which causes it to ionize and give off light. Based on the light we observe, we can successfully infer the mass of the central black hole, which often reaches billions of times the mass of our Sun. Even for the earliest quasars, such as J1342+0928, we can get up to a mass of 800 million solar masses just 690 million years after the Big Bang: when the Universe was just 5% of its current age.

    This artist’s concept shows the most distant supermassive black hole ever discovered. It is part of a quasar from just 690 million years after the Big Bang. Robin Dienel/Carnegie Institution for Science.

    If you try to build a black hole in the conventional way, by having massive stars go supernova, form small black holes, and have them merge together, you run into problems. Star formation is a violent process, as when nuclear fusion ignites, the intense radiation burns off the remaining gas that would otherwise go into forming progressively more and more massive stars. From nearby star-forming regions to the most distant ones we’ve ever observed, this same process seems to be in place, preventing stars (and, hence, black holes) beyond a certain mass from ever forming.

    An artist’s conception of what the Universe might look like as it forms stars for the first time. While stars might reach many hundreds or even a thousand solar masses, it’s very difficult to see how you could get a black hole of the mass the earliest quasars are known to possess. NASA/JPL-Caltech/R. Hurt (SSC).

    We have a standard scenario that’s very powerful and compelling: of supernova explosions, gravitational interactions, and then growth by mergers and accretion. But the early quasars we see are too massive too quickly to be explained by this. Our other known pathway to create black holes, from merging neutron stars, provides no further help. Instead, a third scenario of direct collapse may be responsible. This idea has been helped along by three pieces of evidence in the past year:

    1.The discovery of ultra-young quasars like J1342+0928, in possession of black holes many hundred of millions of solar masses.
    2.Theoretical advances that show how, if the direct collapse scenario is true, we could form early “seed” black holes a thousand times as massive as the ones formed by supernova.
    3.And the discovery of the first stars that become black holes via direct collapse, validating the process.

    In addition to formation by supernovae and neutron star mergers, it should be possible for black holes to form via direct collapse. Simulations such as the one shown here demonstrate that, under the right condition, seed black holes of 100,000 to 1,000,000 solar masses could form in the very early stages of the Universe. Aaron Smith/TACC/UT-Austin.

    Normally, it’s the hottest, youngest, most massive, and newest stars in the Universe that will lead to a black hole. There are plenty of galaxies like this in the early stages of the Universe, but there are also plenty of proto-galaxies that are all gas, dust, and dark matter, with no stars in them yet. Out in the great cosmic abyss, we’ve even found an example of a pair of galaxies just like this: where one has furiously formed stars and the other one may not have formed any yet. The ultra-distant galaxy, known as CR7, has a massive population of young stars, and a nearby patch of light-emitting gas that may not have yet formed a single star in it.

    Illustration of the distant galaxy CR7, which last year was discovered to house a pristine population of stars formed from the material direct from the Big Bang. One of these galaxies definitely houses stars; the other may not have formed any yet. M. Kornmesser / ESO.

    In a theoretical study published in March [Nature Astronomy] of this year, a fascinating mechanism for producing direct collapse black holes from a mechanism like this was introduced. A young, luminous galaxy could irradiate a nearby partner, which prevents the gas within it from fragmenting to form tiny clumps. Normally, it’s the tiny clumps that collapse into individual stars, but if you fail to form those clumps, you instead can just get a monolithic collapse of a huge amount of gas into a single bound structure. Gravitation then does its thing, and your net result could be a black hole over 100,000 times as massive as our Sun, perhaps even all the way up to 1,000,000 solar masses.

    Distant, massive quasars show ultramassive black holes in their cores. It’s very difficult to form them without a large seed, but a direct collapse black hole could solve that puzzle quite elegantly. J. Wise/Georgia Institute of Technology and J. Regan/Dublin City University.

    There are many theoretical mechanisms that turn out to be intriguing, however, that aren’t borne out when it comes to real, physical environments. Is direct collapse possible? We can now definitively answer that question with a “yes,” as the first star that was massive enough to go supernova was seen to simply wink out of existence. No fireworks; no explosion; no increase in luminosity. Just a star that was there one moment, and replaces with a black hole the next. As spotted before-and-after with Hubble, there is no doubt that the direct collapse of matter to a black hole occurs in our Universe.

    The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation. NASA/ESA/C. Kochanek (OSU).

    Put all three of these pieces of information together, and you arrive at the following picture for how these supermassive black holes form so early.

    A region of space collapses to form stars, while a nearby region of space has also undergone gravitational collapse but hasn’t formed stars yet.
    The region with stars emits an intense amount of radiation, where the photon pressure keeps the gas in the other cloud from fragmenting into potential stars.
    The cloud itself continues to collapse, doing so in a monolithic fashion. It expels energy (radiation) as it does so, but without any stars inside.
    When a critical threshold is crossed, that huge amount of mass, perhaps hundreds of thousands or even millions of times the mass of our Sun, directly collapses to form a black hole.
    From this massive, early seed, it’s easy to get supermassive black holes simply by the physics of gravitation, merger, accretion, and time.

    It might not only be possible, but with the new array of radio telescopes coming online, as well as the James Webb Space Telescope, we may be able to witness the process in action.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    SKA Square Kilometer Array

    SKA/ASKAP radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid West region of Western Australia

    SKA Murchison Widefield Array, Boolardy station in outback Western Australia, at the Murchison Radio-astronomy Observatory (MRO)

    The galaxy CR7 is likely one example of many similar objects likely to be out there. As Volker Bromm, the theorist behind the direct collapse mechanism first said [RAS], a nearby, luminous galaxy could cause a nearby cloud of gas to directly collapse. All you need to do is begin with a

    “primordial cloud of hydrogen and helium, suffused in a sea of ultraviolet radiation. You crunch this cloud in the gravitational field of a dark-matter halo. Normally, the cloud would be able to cool, and fragment to form stars. However, the ultraviolet photons keep the gas hot, thus suppressing any star formation. These are the desired, near-miraculous conditions: collapse without fragmentation! As the gas gets more and more compact, eventually you have the conditions for a massive black hole.”

    The directly collapsing star we observed exhibited a brief brightening before having its luminosity drop to zero, an example of a failed supernova. For a large cloud of gas, the luminous emission of light is expected, but no stars are necessary to form a black hole this way.
    NASA/ESA/P. Jeffries (STScI)

    With a little luck, by time 2020 rolls around, this is one longstanding mystery that might finally be solved.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 2:01 pm on November 7, 2017 Permalink | Reply
    Tags: , AGN's - Active galactic nuclei, , , , , , Feeding Black Holes Through Galactic Bars   

    From astrobites via AAS NOVA: ” Feeding Black Holes Through Galactic Bars” 


    Astrobites bloc


    Hubble view of NGC 1300, a barred spiral galaxy. [NASA, ESA, and The Hubble Heritage Team (STScI/AURA)].AAS NOVA

    Title: Galaxy-Scale Bars in Late-Type Sloan Digital Sky Survey Galaxies Do Not Influence the Average Accretion Rates of Supermassive Black Holes
    Authors: A.D. Goulding, E. Matthaey, J.E. Greene, et al.
    First Author’s Institution: Princeton University

    Status: Accepted to ApJ, open access

    When it comes to picking their host galaxies, active galactic nuclei (or AGN) are rather promiscuous. They reside in all types of galaxies: ellipticals, irregulars, and spirals. AGN of the same feather tend to flock together — the more luminous and radio-loud ones are found in elliptical galaxies while the lower luminosity ones are more often found in spiral galaxies. This is a manifestation of the black hole mass-host galaxy luminosity correlation, where spiral galaxies like our Milky Way tend to have less massive black holes than elliptical galaxies. Besides spiral arms, spiral galaxies sometimes also boast of having bars, if the right mood strikes. How are bars related to their AGN? Could they trigger the central black holes to light up as AGN?

    Galactic bars are thought to contribute to the dynamical evolution of their host galaxies. Numerical studies show that they can funnel in gas from the outskirts to the central regions of the galaxies, triggering star formation and possibly AGN activity. It is still unclear whether bars actually help trigger AGN, as previous studies have produced conflicting results and tend to suffer from small number statistics and biased AGN diagnostics. In today’s paper, the authors bring better tools to bear on the problem, by utilizing the large wealth of information from the SDSS Galaxy Zoo citizen science project and X-ray stacking analyses.

    Fig. 1: Sample unbarred (blue borders), ambiguously barred (yellow borders), and barred (red borders) spiral galaxies from the Galaxy Zoo project, as determined by fbar, which is the fraction of votes by citizen scientists for the presence of bars. [Goulding et al. 2017]

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

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