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  • richardmitnick 7:17 pm on September 22, 2016 Permalink | Reply
    Tags: , , , Black Holes   

    From astrobites: “Black holes and populations” 

    Astrobites bloc

    Astrobites

    Sep 22, 2016
    Paddy Alton

    TITLE: Stellar populations across the black hole mass – velocity dispersion relation
    AUTHORS: Ignacio Martín-Navarro, Jean P. Brodie, Remco C. E. van den Bosch, Aaron J. Romanowsky, and Duncan J. Forbes
    FIRST AUTHOR INSTITUTION: University of California Observatories
    STATUS: Accepted for publication in the Astrophysical Journal Letters

    Introduction:

    A supermassive black hole is a kind of cosmic parasite that preys on galaxies. As the host galaxy grows larger, so too does the black hole, consuming gas that would otherwise be turned into stars. Worse, it guzzles gas so quickly that the gas surging down its gravity well gets superheated; the hot gas radiates strongly, heating up surrounding gas and driving it away from the black hole. This prevents it from being turned into stars, causing the galaxy to starve. This effect actually sets a limit on how fast a black hole can grow. To cap it off, it doesn’t always finish its meal, launching jets of material clear of the galaxy which expel yet more gas (there’s an obvious simile here, which I’m not going to employ for reasons of good taste).

    Naturally, all this has a profound effect on the host galaxy and its stellar population, ultimately shutting down star formation. The bigger the galaxy, the bigger the black hole – and the more aggressive it gets. A negative feedback loop is created which causes those galaxies that grow quickest to also fail quickest, a kind of cosmic ‘boom and bust‘. This leads to a tight correlation between the mass of a galaxy’s supermassive black hole and its total mass (more precisely with its velocity dispersion, which is just a stand-in for galaxy mass).

    In today’s paper, the authors search for clues as to how the presence of a supermassive black hole affected the formation of the stars that did make it before the gas supply was cut off.

    How it works:

    We know that just as there is a connection between galaxy mass and black hole mass, so too is there a connection between galaxy mass and the chemical makeup of stars. The most massive galaxies are ‘alpha-enhanced’ – a term that, like most technical language, packs in a lot of detail. Alpha elements are common elements created by sticking together a bunch of alpha particles (Helium nuclei). Their atoms therefore have atomic masses divisible by four: Oxygen, Neon, Magnesium, Silicon, Sulphur, Argon, Calcium, and Titanium, in case you haven’t got a periodic table to hand.

    (Carbon doesn’t count. It’s more like the seed to which you attach alpha particles in order to make the legitimate alpha elements. Making Carbon is hard, but once you’ve got some making alpha elements is easy. Sorry Carbon.)

    There’s another class of elements called ‘iron peak’ elements. Heavier elements tend to be rarer but there’s an exception for elements with atomic numbers similar to iron. When a galaxy is alpha-enhanced, it means that the alpha elements are more abundant relative to the iron peak elements than they are, for example, in the Sun. When this happens it’s actually telling us something interesting about the history of that galaxy. All these elements are formed in stars and released back into the wild via supernova explosions, which come in two types. Core-collapse supernovae are what you’re probably most familiar with: in these a massive star runs out of fuel, can no longer support itself against its own gravity and so collapses … before rebounding in a huge explosion. The massive stars that end in these explosions don’t last long in cosmic terms, sometimes only a few million years. By contrast, other supernovae occur when a white dwarf star (the kind of thing our Sun will eventually turn into) grows above a critical mass, probably due to wrenching material away from another star or merging with another white dwarf. These supernovae almost exclusively make iron peak elements but can’t possibly occur until you actually have some white dwarfs. That means there is a delay of several billion years while you wait for stars like the Sun to reach the end of their lives.

    This time delay is critical. If you grow a galaxy steadily, over billions of years, these late supernova start to go off. This seeds the galaxy with iron peak elements while it’s still making stars. If you grow your galaxy quickly, they still go off, but it’s too late: star formation is finished and those heavy elements sail off into the void. In either case the core-collapse supernovae go off quickly, so you make lots of alpha elements. In summary, alpha-enhancement means you formed your stars very quickly. It’s therefore significant that the most massive galaxies have massive black holes (which we think cut star formation off early on) and are also alpha-enhanced: the two effects are directly related.

    Today’s paper:

    In order to isolate the effect of the black hole, the authors look at the outliers – galaxies whose black holes are a bit more/less massive than expected given the size of the galaxy. This is shown in Figure 1. Their sample spans a wide range of masses and other galaxy properties, the idea being that the particular effect of the black hole can be isolated in this way.

    1
    The authors’ sample of galaxies. The usual relationship between black hole mass and galaxy mass (velocity dispersion, on the x-axis, is just an indirect measurement of this) is plotted as a thick black line. Galaxies with slightly overweight central black holes are in orange, whilst those with comparatively light black holes are in blue (galaxies represented by circles are more compact than those represented by stars, but that’s not very important here). Figure 1 from the paper.

    The authors find a clear correlation between underweight black holes and younger stellar populations, bearing out the idea that less massive central black holes are not so good at cutting off star formation. In the ‘blue’ galaxies in Fig. 1 black hole growth has lagged behind galaxy growth for some reason, which has meant those galaxies were able to form stars for longer.

    2
    Both central black hole mass and the production of alpha elements (see text) such as Magnesium, Mg, are related to galaxy mass. Here we see there is a more fundamental, direct connection between the two: those galaxies with slightly more massive central black holes than expected are also slightly more abundant in Mg than expected (and vice versa). The axes show the excess black hole mass and excess Mg enhancement respectively. Figure 3 from the paper.

    I said earlier that both central black hole mass and enhanced production of alpha elements are linked to total galaxy mass. What the authors are able to show is that there is a more fundamental direct link between the two (see Figure 2); this confirms that these correlations are no coincidence but really do arise from the theory I sketched out. The authors have shown us the direct effects of black hole feedback on the stellar populations of their host galaxies.

    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.

     
  • richardmitnick 4:34 pm on September 13, 2016 Permalink | Reply
    Tags: , , Black Holes, , , Star arrangement that hid for a decade spotted at galaxy’s heart   

    From New Scientist: “Star arrangement that hid for a decade spotted at galaxy’s heart” 

    NewScientist

    New Scientist

    13 September 2016
    Adam Mann

    1
    Part of our galaxy’s centre, as seen in near-infrared wavelengths. ESO/S. Gillessen et al.

    There’s a party in the galactic centre. We may have found the first solid evidence of a dense conference of stars around the Milky Way’s heart, which may one day help us observe the supermassive black hole living there.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    The structure is known as a stellar cusp, and it has played hide-and-seek with astronomers for more than a decade. It was first proposed in the 1970s, when models predicted that stars orbiting a supermassive black hole would jostle around every time one was devoured. Over the course of a galaxy’s lifetime, this should leave an arrangement with many stars near the black hole and exponentially fewer as you move farther away.

    But it has been hard to prove this happens. Other galaxies are too far away for us to see their centres as anything more than fuzzy blobs. Observations in the early 2000s seemed to support a cusp in the Milky Way, but better data showed that we had been tricked by obscuring dust.

    Now, Rainer Schödel at the Institute of Astrophysics of Andalusia in Granada, Spain, and his colleagues have combined images of the galactic centre to map faint old stars, which have been around long enough to settle into a cusp. They also studied the total light emitted by all stars at varying distances from our galaxy’s central black hole, and compared the results with simulations.

    Perfect probes

    These methods point to the same conclusion: the cusp exists. Around our galaxy’s central black hole, the density of stars is 10 million times that in our local area, says Schödel, who presented the work on 7 September at the LISA Symposium in Zurich, Switzerland.

    Many of those stars will eventually explode as supernovae, leaving behind black holes with masses comparable to that of our sun. If one of these merges with the black hole in the galactic centre, it will emit telltale gravitational waves that can be picked up by future observatories, like the proposed Laser Interferometer Space Antenna (LISA).

    ESA/eLISA
    ESA/eLISA

    Those waves will help figure out the mass, rotation rate and other properties of the black hole with extreme precision.

    “These stellar mass black holes would be absolutely perfect probes of spacetime around the supermassive black hole,” Schödel says.

    If the Milky Way has a cusp, then it’s likely that other galaxies do as well. That’s good news for an observatory like LISA, which may be able to pick up waves from dozens or even hundreds of interactions between stellar mass and supermassive black holes each year.

    The work is a significant advance over previous methods and seems to support the existence of a cusp, says Tuan Do at the University of California, Los Angeles. “The galactic centre is always surprising us though, so I think it would be great to take more observations to verify that there is a cusp of faint old stars,” he says.

    The next generation of enormous observatories, like the Thirty Meter Telescope and Giant Magellan Telescope, will see an order of magnitude more stars than current observatories can.

    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA
    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA

    Giant Magellan Telescope, Las Campanas Observatory, to be built  some 115 km (71 mi) north-northeast of La Serena, Chile
    Giant Magellan Telescope, Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile

    They will almost certainly observe the cusp if it’s there, Schödel says.

    See the full article here .

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  • richardmitnick 8:47 pm on September 12, 2016 Permalink | Reply
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    From New Scientist: “First glimpse of a black hole being born from a star’s remains” 

    NewScientist

    New Scientist

    12 September 2016
    Anna Nowogrodzki

    1
    Born phoenix-like from the ashes of a dying star? Science Photo Library/Getty

    We’ve received a birth announcement from 20 million light years away, in the form of our first ever glimpse of what seems to be the birth of a black hole.

    When massive stars run out of fuel, they die in a huge explosion, shooting out high-speed jets of matter and radiation. What’s left behind collapses into a black hole, which is so dense and has such strong gravity that not even light can escape it.

    Or so the theory goes, anyway. Now, a team led by Christopher Kochanek at Ohio State University in Columbus have glimpsed something very special in data from the Hubble Space Telescope, from when it was watching the red supergiant star N6946-BH1, which is about 20 million light years from Earth.

    Fading star

    This star, first observed in 2004, was once about 25 times the mass of our sun. Kochanek and his colleagues found that for some months in 2009, the star briefly flared a million times brighter than our sun, then steadily faded away. New Hubble images show that it has disappeared in visible wavelengths, but a fainter source in the same spot is detectable in the infrared, as a warm afterglow.

    These observations mesh with what theory predicts should happen when a star that size crumples into a black hole. First, the star spews out so many neutrinos that it loses mass. With less mass, the star lacks enough gravity to hold on to a cloud of hydrogen ions loosely bound around it. As this cloud of ions floats away, it cools off, allowing the detached electrons to reattach to the hydrogen. This causes a year-long bright flare – when it fades, only the black hole remains.

    There are two other potential explanations for the star’s disappearing act: it could have merged with another star, or be hidden by dust. But they don’t fit the data: a merger would shine more brightly than the original star for much longer than a few months, and dust wouldn’t hide it for so long.

    “It’s an exciting result and long anticipated,” says Stan Woosley at Lick Observatory in California.

    “This may be the first direct clue to how the collapse of a star can lead to the formation of a black hole,” says Avi Loeb at Harvard University.

    A dark life cycle

    The find needs further confirmation, but that may not be far off. Material falling into the black hole would emit X-rays in a particular spectrum, which could be spotted by the Chandra X-ray Observatory. Kochanek says his group will be getting new data from Chandra in the next two months or so.

    If Chandra sees nothing, that doesn’t mean it’s not a black hole. In any case, the team will continue to look with Hubble – the longer the star is not there, the more likely that it’s a black hole. “Patience proves it no matter what,” says Kochanek.

    This data will help describe the beginning of the life cycle of a black hole, and will inform simulations of how black holes form and what makes a massive star form a neutron star rather than a black hole.

    Despite calling himself a “nasty pessimist”, Kochanek thinks it’s quite likely this is indeed the formation of a black hole. “I’m not quite at ‘I’d bet my life on it’ yet,” he says, “but I’m willing to go for your life.”

    See the full article here .

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  • richardmitnick 11:07 am on September 5, 2016 Permalink | Reply
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    From Ethan Siegel: “What Is The Biggest Black Hole As Seen From Earth?” 

    From Ethan Siegel

    9.5.16

    1
    The supermassive black hole at the core of galaxy NGC 1277 weighs in at 17 billion solar masses. But it’s too distant to be resolved from Earth. Image credit: NASA / ESA / Andrew C. Fabian / Remco C. E. van den Bosch (MPIA).

    If you collapse a large enough mass into a small enough volume, you’ll create a black hole.

    2
    The anatomy of a very massive star throughout its life, culminating in a Type II Supernova. Image credit: Nicole Rager Fuller for the NSF.

    Every object has a gravitational field, and without enough speed, you can’t leave it; you can’t reach escape velocity.

    For black holes, where escape velocity is bigger than the speed of light at the event horizon, nothing can escape, not even light.

    3
    Black holes may still emit light from outside the event horizon, as accelerated matter either falls in or is funneled into jets, but nothing inside the event horizon can ever escape. Image credit: ESO/L. Calçada, of an illustration of the quasar SDSS J1106-1939.

    Black holes are formed from the collapse of incredibly massive objects: ultramassive stars imploding in supernovae at the end of their lives.

    But common, stellar mass black holes, at 1-100 times the Sun’s mass, are surpassed by rarer, supermassive ones.

    4
    The core of galaxy NGC 4261, like the core of a great many galaxies, show signs of a supermassive black hole in both infrared and X-ray observations. Image credit: NASA / Hubble and ESA.

    Almost every galaxy has one, including our Milky Way.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    4
    The largest flare ever observed from the supermassive black hole at our galaxy’s center. Image credit NASA/CXC/Stanford/I. Zhuravleva et al.

    At 4 million solar masses, our black hole is only 26,000 light years away.


    Andrea Ghez, UCLA

    Other, larger, more distant galaxies, like Messier 87, have even larger black holes, reaching into the billions of solar masses.

    5
    Three views of the center of Messier 87 and its central, 6.6 billion solar mass black hole. Images credit: Top, optical, Hubble Space Telescope / NASA / Wikisky, via Wikimedia Commons user Friendlystar; lower left, radio, NRAO / Very Large Array (VLA); lower right, X-ray, NASA / Chandra X-ray telescope.

    Later this decade, an array of radio telescopes — the Event Horizon Telescope — comes online.

    Event Horizon Telescope Array

    Event Horizon Telescope map

    The locations of the radio dishes that will be part of the Event Horizon Telescope array. Image credit: Event Horizon Telescope sites, via University of Arizona at https://www.as.arizona.edu/event-horizon-telescope.

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    With a resolution of 10 micro-arc-seconds (μas), it should see the Milky Way’s supermassive black hole’s event horizon.

    6
    The expected view of the Milky Way’s supermassive black hole through the Event Horizon Telescope. It should be the only one directly visible. Image credit: S. Doeleman et al., via http://www.eventhorizontelescope.org/docs/Doeleman_event_horizon_CGT_CFP.pdf.

    With an angular size of 19 μas, no other black hole appears larger from Earth.

    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 6:44 am on August 23, 2016 Permalink | Reply
    Tags: , , , Black Holes   

    From AAS NOVA: ” When Charged Black Holes Merge” 

    AASNOVA

    American Astronomical Society

    22 August 2016
    Susanna Kohler

    1
    Simulated image of the two merging black holes. New research examines what happens when one of the black holes in a merger is charged. [Cornell SXS Lensing]

    Most theoretical models assume that black holes aren’t charged. But a new study shows that mergers of charged black holes could explain a variety of astrophysical phenomena, from fast radio bursts to gamma-ray bursts.

    No Hair

    The black hole “no hair” theorem states that all black holes can be described by just three things: their mass, their spin, and their charge. Masses and spins have been observed and measured, but we’ve never measured the charge of a black hole — and it’s widely believed that real black holes don’t actually have any charge.

    That said, we’ve also never shown that black holes don’t have charge, or set any upper limits on the charge that they might have. So let’s suppose, for a moment, that it’s possible for a black hole to be charged. How might that affect what we know about the merger of two black holes? A recent theoretical study by Bing Zhang (University of Nevada, Las Vegas) examines this question.

    2
    Intensity profile of a fast radio burst, a sudden burst of radio emission that lasts only a few milliseconds. [Swinburne Astronomy Productions]

    Driving Transients

    Zhang’s work envisions a pair of black holes in a binary system. He argues that if just one of the black holes carries charge — possibly retained by a rotating magnetosphere — then it may be possible for the system to produce an electromagnetic signal that could accompany gravitational waves, such as a fast radio burst or a gamma-ray burst!

    In Zhang’s model, the inspiral of the two black holes generates a global magnetic dipole that’s perpendicular to the plane of the binary’s orbit. The magnetic flux increases rapidly as the separation between the black holes decreases, generating an increasingly powerful magnetic wind. This wind, in turn, can give rise to a fast radio burst or a gamma-ray burst, depending on the value of the black hole’s charge.

    Zhang calculates lower limits on the charge necessary to produce each phenomenon. For a 10-solar-mass black hole, he finds that the merger can generate a fast radio burst if the black hole’s charge is more than ~1012 Coulombs (roughly one billion times the charge that travels through a AA battery from full to empty). If its charge is more than ~1016 Coulombs, it can generate a gamma-ray burst.

    Limits on Charge

    Zhang’s calculations are not just useful in the hypothetical scenario where black holes are charged. They could, in fact, be a way of testing whether black holes are charged.

    As we accumulate future gravitational-wave observations (and with two observations by LIGO already announced, it seems likely that there will be many more), we will grow a larger sample of follow-up observations in radio through gamma-ray wavelengths. Our detections — or our lack of detections — of fast radio bursts or gamma-ray bursts associated with these black-hole mergers will allow us to set some of the first real limits on the charge of black holes.

    Citation

    Bing Zhang 2016 ApJ 827 L31. doi:10.3847/2041-8205/827/2/L31

    See the full article here .

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  • richardmitnick 3:53 pm on August 11, 2016 Permalink | Reply
    Tags: , Black Holes, , ,   

    From New Scientist: “Einstein’s clock: The doomed black hole to set your watch by” 

    NewScientist

    New Scientist

    18 July 2016 [Just appeared in social media.]
    Joshua Sokol

    1
    Caltech/NASA

    Ladies and gentlemen, your challenger. Meet a black hole new to the neighbourhood, weighing 140 million suns. That’s nothing to sneeze at: this plucky upstart is 35 times more massive than the black hole that holds court at the centre of our Milky Way.

    And now, make way for the current champion: a black hole with a mass of 18 billion suns.

    For front-row seats to this cosmic boxing match, you’ll want to (cautiously) approach OJ 287, the core region of a galaxy 3.5 billion light years away. Here, the smaller black hole orbits its larger rival. With every trip around, it falls closer, on track to be swallowed up in about 10,000 years. But in the meantime, it’s putting up an admirable fight.

    Even though the system is so far away, OJ 287 releases enough energy to appear about as bright in the sky as Pluto. We’ve been capturing it on photographic plates since the 1880s, but it first caught the eye of Mauri Valtonen at Finland’s Tuorla Observatory in Turku almost a century later. His team noticed that unlike other galactic centres, which brighten and dim sporadically, this one seemed to keep to a tight schedule. Every 12 years, it has an outburst.

    Well, not exactly every 12 years. Not only do the outbursts look different each time, but the gap between them seems to grow shorter by about 20 days each cycle. In the decades since we noticed the pattern, we’ve gone a long way towards figuring out why.

    2
    S. Zola & NASA/JPL

    Ancient enemies

    OJ 287’s situation is a window into what must have happened in galaxies all over the universe. Galaxies grow by eating their own kind, and almost all of them come with a supermassive black hole at the centre.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    Once two galaxies merge, their black holes – now forced to live in one new mega-galaxy – will either banish their rival with a gravitational kick that flings their opponent out of the galaxy, or eventually merge into an even bigger black hole.

    In OJ 287, the smaller black hole is en route to becoming a snack for the larger one. The larger one is also growing from a surrounding disc of gas and dust, the material from which slowly swirls down the drain. Each time the smaller black hole completes an orbit, it comes crashing through this disc at supersonic speeds.

    That violent impact blows bubbles of hot gas that expand, thin out, and then unleash a flood of ultraviolet radiation – releasing as much energy as 20,000 supernova explosions in the same spot. You could stand 36 light years away and tan faster than you would from the sun on Earth.

    The cymbal clash to come

    Even with all this thrashing, the smaller black hole has no chance of escape. Energy leaches away from the binary orbit, bringing the pair closer together and making each cycle around the behemoth a little shorter than the last.

    Although the outbursts may be impressive, the black holes’ orbital dance emits tens of thousands of times more energy as undulations in space time called gravitational waves.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    Last year, the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the US offered a preview of the endgame of OJ 287 in miniature.

    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Twice in 2015, LIGO heard gravitational waves from the final orbits of black-hole pairs in which each black hole was a few dozen times the size of the sun, and then the reverberations of the single one left behind.

    SXS, the Simulating eXtreme Spacetimes (SXS) project
    SXS, the Simulating eXtreme Spacetimes (SXS) project

    Because its black holes are so massive, the ultimate collision at the heart of OJ 287 will be too low-frequency for LIGO to hear. But the outcome will be much the same. Where once two black holes from two separate galaxies tussled, one black hole will remain, smug and secure at the centre.

    See the full article here .

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  • richardmitnick 11:09 am on August 7, 2016 Permalink | Reply
    Tags: , , , Black Holes   

    From Astronomy Now: “Do black holes have a back door?” 

    Astronomy Now bloc

    Astronomy Now

    6 August 2016
    No writer credit found

    1
    In the 2014 science fiction film Interstellar, a group of astronauts traverse a wormhole near a black hole called Gargantua. A recent study by researchers at the Institute of Corpuscular Physics in Valencia suggests that matter might indeed survive its foray into these space objects and come out the other side. Illustration: A realistic accretion disc gravitationally lensed by a rotating black hole. Credit: Double Negative artists/DNGR/TM & © Warner Bros. Entertainment Inc./ Creative Commons (CC BY-NC-ND 3.0) license.

    One of the biggest problems when studying black holes is that the laws of physics as we know them cease to apply in their deepest regions. Large quantities of matter and energy concentrate in an infinitely small space, the gravitational singularity, where space-time curves towards infinity and all matter is destroyed. Or is it?

    A recent study by researchers at the Institute of Corpuscular Physics (IFIC, CSIC-UV) in Valencia suggests that matter might in fact survive its foray into these space objects and come out the other side.

    Published in the journal Classical and Quantum Gravity, the Valencian physicists propose considering the singularity as if it were an imperfection in the geometric structure of space-time. And by doing so they resolve the problem of the infinite, space-deforming gravitational pull.

    “Black holes are a theoretical laboratory for trying out new ideas about gravity,” says Gonzalo Olmo, a Ramón y Cajal grant researcher at the Universitat de València (University of Valencia, UV). Alongside Diego Rubiera, from the University of Lisbon, and Antonio Sánchez, PhD student also at the UV, Olmo’s research sees him analysing black holes using theories besides general relativity (GR).

    Specifically, in this work he has applied geometric structures similar to those of a crystal or graphene layer, not typically used to describe black holes, since these geometries better match what happens inside a black hole: “Just as crystals have imperfections in their microscopic structure, the central region of a black hole can be interpreted as an anomaly in spacetime, which requires new geometric elements in order to be able to describe them more precisely. We explored all possible options, taking inspiration from facts observed in nature.”

    Using these new geometries, the researchers obtained a description of black holes whereby the centre point becomes a very small spherical surface. This surface is interpreted as the existence of a wormhole within the black hole. “Our theory naturally resolves several problems in the interpretation of electrically-charged black holes,” Olmo explains. “In the first instance we resolve the problem of the singularity, since there is a door at the centre of the black hole, the wormhole, through which space and time can continue.”

    This study is based on one of the simplest known types of black hole, rotationless and electrically-charged. The wormhole predicted by the equations is smaller than an atomic nucleus, but gets bigger the bigger the charge stored in the black hole. So, a hypothetical traveller entering a black hole of this kind would be stretched to the extreme, or “spaghettified,” and would be able to enter the wormhole. Upon exiting they would be compacted back to their normal size.

    Seen from outside, these forces of stretching and compaction would seem infinite, but the traveller himself, living it first-hand, would experience only extremely intense, and not infinite, forces. It is unlikely that the star of Interstellar would survive a journey like this, but the model proposed by IFIC researchers posits that matter would not be lost inside the singularity, but rather would be expelled out the other side through the wormhole at its centre to another region of the universe.

    Another problem that this interpretation resolves, according to Olmo, is the need to use exotic energy sources to generate wormholes. In Einstein’s theory of gravity, these “doors” only appear in the presence of matter with unusual properties (a negative energy pressure or density), something which has never been observed. “In our theory, the wormhole appears out of ordinary matter and energy, such as an electric field” (Olmo).

    The interest in wormholes for theoretical physics goes beyond generating tunnels or doors in spacetime to connect two points in the universe. They would also help explain phenomena such as quantum entanglement or the nature of elementary particles. Thanks to this new interpretation, the existence of these objects could be closer to science than fiction.

    See the full article here .

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  • richardmitnick 11:33 am on August 1, 2016 Permalink | Reply
    Tags: , , Black Holes,   

    From Sploid: “How Black Holes Can Kill Us From Light Years Away” 

    SPLOID bloc

    SPLOID

    8.1.16
    Bryan Menegus

    1
    No image caption. No image credit.

    The Earth isn’t particularly close to any black holes—the closest candidate, A0620-00, is around 2,800 light years away—so good on us for picking a nice cosmic neighborhood to live in. But besides the whole “nothing escapes from them” thing and the hugely destructive supernova preceding their birth, black holes are bad news. They could end life as we know it, even from far away.

    Right after a star collapses into a black hole (or two stars collide to do the same) a tremendous amount of energy is released as a gamma ray burst, Kurzgesagt explains. The ozone layer around Earth generally protects us from the gamma rays given off by our own sun, but a full-blown gamma ray burst is so much more powerful that it would cook the side of our planet that came in contact with it. Gamma rays are also capable of blowing apart the bonds in our DNA. Because these bursts are invisibly and move at the speed of light we probably wouldn’t know one was coming until it was too late. One minute the Eastern Hemisphere is going about its business; the next it’s a Mad Max wasteland.

    The good news is that gamma ray bursts don’t happen all that often, and one would have to be coming from within our own galaxy in order to be of serious danger. Between the timescale required, number of black hole candidates nearby, and likeliness of a direct hit, Earth has more pressing things to worry about—like climate change, a Trump presidency, or whether we’ll ever see a new season of Attack on Titan.

    See the full article here .

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  • richardmitnick 1:30 pm on July 29, 2016 Permalink | Reply
    Tags: , , Black Holes,   

    From CfA: “The Aligned Spin of a Black Hole” 

    Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory

    July 29, 2016
    No writer credit

    1
    An artist’s conception of an X-ray emitting black hole binary system. A new study has measured the spin of one notable example and confirmed, contrary to some earlier claims, that the spin is aligned with the spin of the accretion disk. NASA/ESA

    A black hole in traditional theory is characterized by having “no hair,” that is, it is so simple that it can be completely described by just three parameters, its mass, its spin, and its electric charge. Even though it may have formed out of a complex mix of matter and energy, all the specific details are lost when it collapses to a singular point. This is surrounded by a “horizon,” and once anything – matter or light (energy) – falls within that horizon, it cannot escape. Hence, the singularity appears black. Outside this horizon a rotating, accreting disk can radiate freely.

    Astronomers are able to measure the spins of black holes by closely modeling the X-ray radiation from the environment in one of two ways: fitting the continuum emission spectrum, or modeling the shape of an emission iron line from very highly ionized iron. So far the spins of ten stellar-mass black holes have been determined and the robustness of the continuum-fitting method has been well demonstrated. Recently one bright black hole, “Nova Muscae 1991,” was found to be rotating in a sense opposite to the spin of its disk, a very unusual and curious result since both might be expected to develop somewhat in concert. The spin of this black hole had previously determined to be small, about ten percent of the limit allowed by relativity.

    CfA astronomers Jeff McClintock, James Steiner and Jainfeng Wu and their colleagues have re-reduced archival data for this source, and obtained much improved measurements for the three key parameters needed in the continuum-fitting method: mass (11.0 solar-masses), disk inclination (43.2 degrees), and distance (16,300 light-years), each with a corresponding (and modest) uncertainty. Using the new numbers to reevaluate the model of the Nova Muscae 1991 spin, the scientists report that the spin is actually about five times larger than previously estimated. More significantly, that the spin is definitely prograde (aligned with the direction of the disk spin), and not retrograde. The new results resolve a potential mystery, and offer a confirmation of the general methods for modeling black holes.

    Reference(s):

    The Spin of The Black Hole in the X-ray Binary Nova Muscae 1991, Zihan Chen, Lijun Gou, Jeffrey E. McClintock, James F. Steiner, Jianfeng Wu, Weiwei Xu, Jerome A. Orosz, and Yanmei Xiang, ApJ 825, 45, 2016.

    See the full article here .

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    About CfA

    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. The long relationship between the two organizations, which began when the SAO moved its headquarters to Cambridge in 1955, was formalized by the establishment of a joint center in 1973. The CfA’s history of accomplishments in astronomy and astrophysics is reflected in a wide range of awards and prizes received by individual CfA scientists.

    Today, some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies. These scientific investigations, touching on almost all major topics in astronomy, are organized into the following divisions, scientific departments and service groups.

     
  • richardmitnick 9:23 am on July 26, 2016 Permalink | Reply
    Tags: , , Black Holes,   

    From Science Alert: “Astronomers just discovered a “stealth black hole” hiding inside our galaxy” 

    ScienceAlert

    Science Alert

    1
    Image: X-ray: NASA/CXC/Univ. of Alberta/B.Tetarenko et al; Optical: NASA/STScI; Radio: NSF/NRAO/VLA/Curtin Univ./J. Miller-Jones

    28 JUN 2016
    DAVID NIELD

    Scientists have just discovered a ‘hidden’ black hole, called VLA J2130+12, hiding inside the Milky Way. The reason it has eluded astronomers until now is that it hasn’t been acting the way black holes normally do.

    Simply put, this black hole is quieter than we might expect and is in many ways a “stealth black hole”, as one of the astronomers describes it. It’s pulling in nearby material, like all black holes do, but at a very slow rate – and that’s why it’s previously been missed.

    What’s more, the new discovery indicates there might be millions of these stealth black holes hidden across the Universe waiting to be discovered. Astronomers: recalibrate your telescopes.

    Spotting black holes isn’t quite as simple as pointing a telescope at the sky – we can only really ‘see’ them based on the effect they have on nearby matter, which means these celestial phenomena can go undetected for a very long time.

    “Usually, we find black holes when they are pulling in lots of material,” explained lead researcher Bailey Tetarenko from the University of Alberta in Canada. “Before falling into the black hole this material gets very hot and emits brightly in X-rays. This one is so quiet that it’s practically a stealth black hole.”

    A “peculiar” source of radio waves first tipped off experts to the presence of this black hole.

    These radio waves were being emitted as strongly as if they were coming from a black hole, but the researchers were only detecting faint pulses of X-rays, which doesn’t match up with our understanding of how black holes work. The team realised that these weak X-rays were a result of the black hole working so slowly.

    VLA J2130+12 has about one-tenth to one-fifth the mass of our own Sun and is 7,200 light-years away, which is well inside our own Milky Way. According to the researchers behind the new discovery, some of these hidden black holes could be even closer to Earth: thankfully though they’ll still be many light years away, so there’s no danger of us being sucked into a void just yet.

    2
    Astronomers used data from some serious bits of space kit to work out exactly what VLA J2130+12 is. They combined readings from NASA’s Chandra X-ray Observatory, the Hubble Space Telescope, and the Karl G. Jansky Very Large Array (VLA).

    Many more regions of the sky will need to be mapped in this kind of detail if we’re to spot other stealth black holes like this one.

    “Unless we were incredibly lucky to find one source like this in a small patch of the sky, there must be many more of these black hole binaries in our Galaxy than we used to think,” said one of the researchers, Arash Bahramian from the University of Alberta.

    The findings are published in The Astrophysical Journal.

    See the full article here .

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