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  • richardmitnick 10:00 pm on June 14, 2021 Permalink | Reply
    Tags: "Black holes help with star birth", Cosmic mass monsters clear the way for the formation of new suns in satellite galaxies., , , The IllustrisTNG Project, Women in STEM-Annalisa Pillepich   

    From MPG Institute for Astronomy [MPG Institut für Astronomie] (DE) : Women in STEM-Annalisa Pillepich “Black holes help with star birth” 

    Max Planck Institut für Astronomie (DE)

    From MPG Institute for Astronomy [MPG Institut für Astronomie] (DE)

    June 09, 2021

    Markus Pössel
    Head of press and public relations
    Max Planck Institute for Astronomy, Heidelberg
    +49 6221 528-261
    Annalisa Pillepich
    Max Planck Institute for Astronomy, Heidelberg
    +49 6221 528-395

    The cosmic mass monsters clear the way for the formation of new suns in satellite galaxies.

    Research combining systematic observations with cosmological simulations has found that, surprisingly, black holes can help certain galaxies form new stars. On scales of galaxies, the role of supermassive black holes for star formation had previously been seen as destructive – active black holes can strip galaxies of the gas that galaxies need to form new stars. The new results, published in the journal Nature, showcase situations where active black holes can, instead, “clear the way” for galaxies that orbit inside galaxy groups or clusters, keeping those galaxies from having their star formation disrupted as they fly through the surrounding intergalactic gas.

    Virtual milky way: Gas density around a massive central galaxy in a group in the virtual universe of the TNG50 simulation. Gas inside the galaxy corresponds to the bright vertical structure: a gaseous disk. To the left and right of that structure are bubbles – regions that look like circles in this image, with markedly reduced gas density inside. This geometry of the gas is due to the action of the super massive black hole that hides at the center of the galaxy and that pushes out gas preferably in directions perpendicular to the galaxy gaseous disk, carving regions of lower density. © Dylan Nelson/TNG Collaboration.

    Active black holes are primarily thought to have a destructive influence on their surroundings. As they blast energy into their host galaxy, they heat up and eject that galaxy’s gas, making it more difficult for the galaxy to produce new stars. But now, researchers have found that the same activity can actually help with star formation – at least for the satellite galaxies that orbit the host galaxy.

    The counter-intuitive result came out of a collaboration sparked by a lunchtime conversation between astronomers specializing in large-scale computer simulations and observers. As such, it is a good example for the kind of informal interaction that has become more difficult under pandemic conditions.

    Astronomical observations that include taking a distant galaxy’s spectrum – the rainbow-like separation of a galaxy’s light into different wavelengths – allow for fairly direct measurements of the rate at which that galaxy is forming new stars.

    Going by such measurements, some galaxies are forming stars at rather sedate rates. In our own Milky Way galaxy, only one or two new stars are born each year. Others undergo brief bursts of excessive star formation activity, called “star bursts”, with hundreds of stars born per year. In yet other galaxies, star formation appears to be suppressed, or “quenched,” as astronomers say: Such galaxies have virtually stopped forming new stars.

    A special kind of galaxy, specimens of which are frequently – almost half of the time – found to be in such a quenched state, are so-called satellite galaxies. These are part of a group or cluster of galaxies, their mass is comparatively low, and they orbit a much more massive central galaxy similar to the way satellites orbit the Earth.

    Such galaxies typically form very few new stars, if at all, and since the 1970s, astronomers have suspected that something very much akin to headwind might be to blame: Groups and clusters of galaxies not only contain galaxies, but also rather hot thin gas filling the intergalactic space.

    As a satellite galaxy orbits through the cluster at a speed of hundreds of kilometers per second, the thin gas would make it feel the same kind of “headwind” that someone riding a fast bike, or motor-bike, will feel. The satellite galaxy’s stars are much too compact to be affected by the steady stream of oncoming intergalactic gas.

    But the satellite galaxy’s own gas is not: It would be stripped away by the oncoming hot gas in a process known as “ram pressure stripping”. On the other hand, a fast-moving galaxy has no chance of pulling in a sufficient amount of intergalactic gas, to replenish its gas reservoir. The upshot is that such satellite galaxies lose their gas almost completely – and with it the raw material needed for star formation. As a result, star-formation activity would be quenched.

    The processes in question take place over millions or even billions of years, so we cannot watch them happening directly. But even so, there are ways for astronomers to learn more. They can utilize computer simulations of virtual universes, programmed so as to follow the relevant laws of physics – and compare the results with what we actually observe. And they can look for tell-tale clues in the comprehensive “snapshot” of cosmic evolution that is provided by astronomical observations.

    Annalisa Pillepich, a group leader at the MPG Institute for Astronomy [MPG Institut für Astronomie](DE), specializes in simulations of this kind. The IllustrisTNG suite of simulations, which Pillepich has co-led, provides the most detailed virtual universes to date – universes in which researchers can follow the movement of gas around on comparatively small scales.

    IllustrisTNG provides some extreme examples of satellite galaxies that have freshly been stripped by ram pressure: so-called “jellyfish galaxies,” that are trailing the remnants of their gas like jellyfish are trailing their tentacles. In fact, identifying all the jellyfish in the simulations is a recently launched citizen science project on the Zooniverse platform, where volunteers can help with the research into that kind of freshly quenched galaxy.

    But, while jellyfish galaxies are relevant, they are not where the present research project started. Over lunch in November 2019, Pillepich recounted a different one of her IllustrisTNG results to Ignacio Martín-Navarro, an astronomer specializing in observations, who was at MPIA on a Marie Curie fellowship. A result about the influence of supermassive black holes that reached beyond the host galaxy, into intergalactic space.

    Such supermassive black holes can be found in the center of all galaxies. Matter falling onto such a black hole typically becomes part of a rotating so-called accretion disk surrounding the black hole, before falling into the black hole itself. This fall onto the accretion disk liberates an enormous amount of energy in the form of radiation, and oftentimes also in the form of two jets of quickly moving particles, which accelerate away from the black hole at right angles to the accretion disk. A supermassive black hole that is emitting energy in this way is called an Active Galactic Nucleus, AGN for short.

    While IllustrisTNG is not detailed enough to include black hole jets, it does contain physical terms that simulate how an AGN is adding energy to the surrounding gas. And as the simulation showed, that energy injection will lead to gas outflows, which in turn will orient themselves along a path of least resistance: in the case of disk galaxies similar to our own Milky Way, perpendicular to the stellar disk; for so-called elliptical galaxies, perpendicular to a suitable preferred plane defined by the arrangement of the galaxy’s stars.

    Over time, the bipolar gas outflows, perpendicular to the disk or preferred plane, will go so far as to affect the intergalactic environment – the thin gas surrounding the galaxy. They will push the intergalactic gas away, each outflow creating a gigantic bubble. It was this account that got Pillepich and Martín-Navarro thinking: If a satellite galaxy were to pass through that bubble – would it be affected by the outflow, and would its star formation activity be quenched even further?

    Martín-Navarro took up this question within his own domain. He had extensive experience in working with data from one of the largest systematic surveys to date: the Sloan Digital Sky Survey (SDSS), which provides high-quality images of a large part of the Northern hemisphere. In the publicly available data from that survey’s 10th data, he examined 30,000 galaxy groups and clusters, each containing a central galaxy and on average 4 satellite galaxies.

    In a statistical analysis of those thousands of systems, he found a small, but marked difference between satellite galaxies that were close to the central galaxy’s preferred plane and satellites that were markedly above and below. But the difference was in the opposite direction the researchers had expected: Satellites above and below the plane, within the thinner bubbles, were on average not more likely, but about 5% less likely to have had their star formation activity quenched.

    With that surprising result, Martín-Navarro went back to Annalisa Pillepich, and the two performed the same kind of statistical analysis in the virtual universe of the IllustrisTNG simulations. In simulations of that kind, after all, cosmic evolution is not put in “by hand” by the researchers. Instead, the software includes rules that model the rules of physics for that virtual universe as naturally as possible, and which also include suitable initial conditions that correspond to the state of our own universe shortly after the Big Bang.

    That is why simulations like that leave room for the unexpected – in this particular case, for re-discovering the on-plane, off-plane distribution of quenched satellite galaxies: The virtual universe showed the same 5% deviation for the quenching of satellite galaxies! Evidently, the researchers were on to something.

    In time, Pillepich, Martín-Navarro and their colleagues came up with a hypothesis for the physical mechanism behind the quenching variation. Consider a satellite galaxy travelling through one of the thinned-out bubbles the central black hole has blown into the surrounding intergalactic medium. Due to the lower density, that satellite galaxy experiences less headwind, less ram pressure, and is thus less likely to have its gas stripped away.

    Then, it is down to statistics. For satellite galaxies that have orbited the same central galaxies several times already, traversing bubbles but also the higher-density regions in between, the effect will not be noticeable. Such galaxies will have lost their gas long ago.

    But for satellite galaxies that have joined the group, or cluster, rather recently, location will make a difference: If those satellites happen to land in a bubble first, they are less likely to lose their gas then if they happen to land outside a bubble. This effect could account for the statistical difference for the quenched satellite galaxies.

    With the excellent agreement between the statistical analyses of both the SDSS observations and the IllustrisTNG simulations, and with a plausible hypothesis for a mechanism, this is a highly promising result. In the context of galaxy evolution, it is particularly interesting because it confirms, indirectly, the role of active galactic nuclei not only heating intergalactic gas up, but actively “pushing it away”, to create lower-density regions. And as with all promising results, there are now a number of natural directions that either Martín-Navarro, Pillepich and their colleagues or other scientists can take in order to explore further.

    See the full article here .


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    Max Planck Institute for Astronomy, Heidelburg, GE

    The MPG Institute for Astronomy [MPG Institut für Astronomie] (DE), MPIA) is a research institute of the Max Planck Society (MPG). It is located in Heidelberg, Baden-Württemberg, Germany near the top of the Königstuhl, adjacent to the historic Landessternwarte Heidelberg-Königstuhl astronomical observatory. The institute primarily conducts basic research in the natural sciences in the field of astronomy.

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    MPG Society for the Advancement of Science [MPG Gesellschaft zur Förderung der Wissenschaften e. V.] 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.
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    The Max Planck Society and its predecessor Kaiser Wilhelm Society hosted several renowned scientists in their fields, including Otto Hahn, Werner Heisenberg, and Albert Einstein.
    The organization was established in 1911 as the Kaiser Wilhelm Society, or Kaiser-Wilhelm-Gesellschaft (KWG), a non-governmental research organization named for the then German emperor. The KWG was one of the world’s leading research organizations; its board of directors included scientists like Walther Bothe, Peter Debye, Albert Einstein, and Fritz Haber. In 1946, Otto Hahn assumed the position of President of KWG, and in 1948, the society was renamed the Max Planck Society (MPG) after its former President (1930–37) Max Planck, who died in 1947.
    The Max Planck Society has a world-leading reputation as a science and technology research organization. In 2006, the Times Higher Education Supplement rankings of non-university research institutions (based on international peer review by academics) placed the Max Planck Society as No.1 in the world for science research, and No.3 in technology research (behind AT&T Corporation and the DOE’s Argonne National Laboratory (US).
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    The Max Planck Society consists of over 80 research institutes. In addition, the society funds a number of Max Planck Research Groups (MPRG) and International Max Planck Research Schools (IMPRS). The purpose of establishing independent research groups at various universities is to strengthen the required networking between universities and institutes of the Max Planck Society.
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    International Max Planck Research Schools
    Together with the Association of Universities and other Education Institutions in Germany, the Max Planck Society established numerous International Max Planck Research Schools (IMPRS) to promote junior scientists:
    Cologne Graduate School of Ageing Research, Cologne
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    International Max Planck Research School on Adapting Behavior in a Fundamentally Uncertain World (Uncertainty School), at the Max Planck Institutes for Economics, for Human Development, and/or Research on Collective Goods
    International Max Planck Research School for Analysis, Design and Optimization in Chemical and Biochemical Process Engineering, Magdeburg
    International Max Planck Research School for Astronomy and Cosmic Physics, Heidelberg at the MPG for Astronomy
    International Max Planck Research School for Astrophysics, Garching at the MPG Institute for Astrophysics
    International Max Planck Research School for Complex Surfaces in Material Sciences, Berlin
    International Max Planck Research School for Computer Science, Saarbrücken
    International Max Planck Research School for Earth System Modeling, Hamburg
    International Max Planck Research School for Elementary Particle Physics, Munich, at the MPG Institute for Physics
    International Max Planck Research School for Environmental, Cellular and Molecular Microbiology, Marburg at the MPG Institute for Terrestrial Microbiology
    International Max Planck Research School for Evolutionary Biology, Plön at the Max Planck Institute for Evolutionary Biology
    International Max Planck Research School “From Molecules to Organisms”, Tübingen at the MPG Institute for Developmental Biology
    International Max Planck Research School for Global Biogeochemical Cycles, Jena at the Max Planck Institute for Biogeochemistry
    International Max Planck Research School on Gravitational Wave Astronomy, Hannover and Potsdam MPG Institute for Gravitational Physics
    International Max Planck Research School for Heart and Lung Research, Bad Nauheim at the MPG Institute for Heart and Lung Research
    International Max Planck Research School for Infectious Diseases and Immunity, Berlin at the Max Planck Institute for Infection Biology
    International Max Planck Research School for Language Sciences, Nijmegen
    International Max Planck Research School for Neurosciences, Göttingen
    International Max Planck Research School for Cognitive and Systems Neuroscience, Tübingen
    International Max Planck Research School for Marine Microbiology (MarMic), joint program of the MPG Institute for Marine Microbiology in Bremen, the University of Bremen (DE), the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, and the Jacobs University Bremen
    International Max Planck Research School for Maritime Affairs, Hamburg
    International Max Planck Research School for Molecular and Cellular Biology, Freiburg
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    International Max Planck Research School for Molecular Biology, Göttingen
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    International Max Planck Research School on Multiscale Bio-Systems, Potsdam
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    International Max Planck Research School on Reactive Structure Analysis for Chemical Reactions (IMPRS RECHARGE), Mülheim an der Ruhr, at the Max Planck Institute for Chemical Energy Conversion (DE)
    International Max Planck Research School for Science and Technology of Nano-Systems, Halle at MPG Institute of Microstructure Physics (DE)
    International Max Planck Research School for Solar System Science[49] at theUniversity of Göttingen – Georg-August-Universität Göttingen (DE) hosted by MPG Institute for Solar System Research [Max-Planck-Institut für Sonnensystemforschung] (DE)
    International Max Planck Research School for Astronomy and Astrophysics, Bonn, at the MPG Institute for Radio Astronomy [MPG Institut für Radioastronomie](DE) (formerly the International Max Planck Research School for Radio and Infrared Astronomy)
    International Max Planck Research School for the Social and Political Constitution of the Economy, Cologne
    International Max Planck Research School for Surface and Interface Engineering in Advanced Materials, Düsseldorf at MPG Institute for Iron Research [MPG Institut für Eisenforschung] (DE)
    International Max Planck Research School for Ultrafast Imaging and Structural Dynamics, Hamburg

  • richardmitnick 11:50 am on June 2, 2020 Permalink | Reply
    Tags: "Galactic Star Formation and Supermassive Black Hole Masses", , , , , , The IllustrisTNG Project   

    From Harvard-Smithsonian Center for Astrophysics: “Galactic Star Formation and Supermassive Black Hole Masses” 

    Harvard Smithsonian Center for Astrophysics

    From Harvard-Smithsonian Center for Astrophysics

    May 29, 2020

    A simulation of the stellar content of the universe today seen across one hundred million light-years. Astronomers used this simulation to investigate how accretion onto a supermassive black hole quenches galaxy star formation. Credit: The IllustrisTNG Project

    Astronomers studying how star formation evolved over cosmic time have discovered that quiescent galaxies (galaxies that are currently not making many new stars) frequently have active galactic nuclei. These AGN accrete material onto hot circumnuclear disks, and the resultant energy is released in bursts of radiation, or as jets of particles moving at close to the speed of light. The suspicion is that these outbursts drive gas outflows over thousands of light-years, disrupting and dispersing potential star forming material in a process called quenching. The quenching mechanism is in addition a self-limiting one since the dispersion ultimately suppresses the gas accretion onto the black hole itself. There are other proposed mechanisms for quenching however: supernovae produced during star formation could be responsible (or at least an important contributor) as could strong stellar winds. Verifying these various alternatives is hence a key goal of galactic research.

    CfA astronomers Bryan Terrazas, Rainer Weinberger and Lars Hernquist and their colleagues used the large-scale hydrodynamic simulation called IllustrisTNG to trace the development of galaxies and their black holes, in particular to investigate the correlations between black hole feedback and the suppression of star formation. Although the details of black hole accretion are still only sketchily understood, the simulation allows scientists to vary many input parameters of the simulation to test a range of alternatives.

    The astronomers find that galaxies in the local universe with more than about ten billion masses of stars will indeed tend to quench star production once the energy in the winds from black hole accretion becomes larger than the gravitational energy in the gas, and that this tends to happen when the mass of the supermassive black hole exceeds about one hundred and sixty million solar masses. This value appears to be quite sharply delineated: 90% of galaxies with smaller black holes are actively star forming and 90% of galaxies with larger black holes are quiescent. The team then compared the results of the simulations to observations of ninety one galaxies (although not a completely representative sample of objects) and finds generally good agreement; however, the observations show a much larger range of behavior.

    Science paper:
    “The Relationship between Black Hole Mass and Galaxy Properties: Examining the Black Hole Beedback Model in IllustrisTNG”

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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.

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