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  • 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

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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
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    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.

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  • richardmitnick 1:30 pm on July 29, 2016 Permalink | Reply
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    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
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    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.

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  • richardmitnick 3:39 pm on July 18, 2016 Permalink | Reply
    Tags: , , Black Holes, , OJ 287   

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

    NewScientist

    New Scientist

    18 July 2016
    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.

    1
    OJ 287

    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.

    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.

    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.

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

    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 4:17 pm on July 12, 2016 Permalink | Reply
    Tags: , , Black Holes, Gravitational vortex, ,   

    From U Cambridge: “Gravitational vortex provides new way to study matter close to a black hole” 

    U Cambridge bloc

    Cambridge University

    12 Jul 2016
    No writer credit found

    1
    Illustration of gravitational vortex. Credit: ESA/ATG medialab

    An international team of astronomers has proved the existence of a ‘gravitational vortex’ around a black hole, solving a mystery that has eluded astronomers for more than 30 years. The discovery will allow astronomers to map the behaviour of matter very close to black holes. It could also open the door to future investigation of Albert Einstein’s general relativity.

    Matter falling into a black hole heats up as it plunges to its doom. Before it passes into the black hole and is lost from view forever, it can reach millions of degrees. At that temperature it shines x-rays into space.

    In the 1980s, astronomers discovered that the x-rays coming from black holes vary on a range of timescales and can even follow a repeating pattern with a dimming and re-brightening taking 10 seconds to complete. As the days, weeks and then months progress, the pattern’s period shortens until the oscillation takes place 10 times every second. Then it suddenly stops altogether.

    This phenomenon was dubbed a Quasi Periodic Oscillation (QPO). During the 1990s, astronomers began to suspect that the QPO was associated with a gravitational effect predicted by Einstein’s general relativity which suggested that a spinning object will create a kind of gravitational vortex. The effect is similar to twisting a spoon in honey: anything embedded in the honey will be ‘dragged’ around by the twisting spoon. In reality, this means that anything orbiting around a spinning object will have its motion affected. If an object is orbiting at an angle, its orbit will ‘precess’ – in other words, the whole orbit will change orientation around the central object. The time for the orbit to return to its initial condition is known as a precession cycle.

    In 2004, NASA launched Gravity Probe B to measure this so-called Lense-Thirring effect around Earth.

    NASA/Gravity Probe B
    NASA/Gravity Probe B

    By analysing the resulting data, scientists confirmed that the spacecraft would turn through a complete precession cycle once every 33 million years. Around a black hole, however, the effect would be much stronger because of the stronger gravitational field: the precession cycle would take just a matter of seconds to complete, close to the periods of the QPOs.

    An international team of researchers, including Dr Matt Middleton from the Institute of Astronomy at the University of Cambridge, has used the European Space Agency’s XMM-Newton and NASA’s NuSTAR, both x-ray observatories, to study the effect of black hole H1743-322 on a surrounding flat disc of matter known as an ‘accretion disk’.

    ESA/XMM Newton
    ESA/XMM Newton

    NASA/NuSTAR
    NASA/NuSTAR

    Close to a black hole, the accretion disc puffs up into a hot plasma, a state of matter in which electrons are stripped from their host atoms – the precession of this puffed up disc has been suspected to drive the QPO. This can also explain why the period changes – the place where the disc puffs up gets closer to the black hole over weeks and months, and, as it gets closer to the black hole, the faster its Lense-Thirring precession becomes.

    2

    The plasma releases high energy radiation that strikes the matter in the surrounding accretion disc, making the iron atoms in the disc shine like a fluorescent light tube. Instead of visible light, the iron releases X-rays of a single wavelength – referred to as ‘a line’. Because the accretion disc is rotating, the iron line has its wavelength distorted by the Doppler effect: line emission from the approaching side of the disc is squashed – blue shifted – and line emission from the receding disc material is stretched – red shifted. If the plasma really is precessing, it will sometimes shine on the approaching disc material and sometimes on the receding material, making the line wobble back and forth over the course of a precession cycle.

    It is this ‘wobble’ that has been observed by the researchers.

    “Just as general relativity predicts, we’ve seen the iron line wobble as the accretion disk orbits the black hole,” says Dr Middleton. “This is what we’d expect from matter moving in a strong gravitational field such as that produced by a black hole.”

    This is the first time that the Lense-Thirring effect has been measured in a strong gravitational field. The technique will allow astronomers to map matter in the inner regions of accretion discs around back holes. It also hints at a powerful new tool with which to test general relativity. Einstein’s theory is largely untested in such strong gravitational fields. If astronomers can understand the physics of the matter that is flowing into the black hole, they can use it to test the predictions of general relativity as never before – but only if the movement of the matter in the accretion disc can be completely understood.

    “We need to test Einstein’s general theory of relativity to breaking point,” adds Dr Adam Ingram, the lead author at the University of Amsterdam. “That’s the only way that we can tell whether it is correct or, as many physicists suspect, an approximation – albeit an extremely accurate one.”

    Larger X-ray telescopes in the future could help in the search because they could collect the X-rays faster. This would allow astronomers to investigate the QPO phenomenon in more detail. But for now, astronomers can be content with having seen Einstein’s gravity at play around a black hole.

    See the full article here .

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    U Cambridge Campus

    The University of Cambridge (abbreviated as Cantab in post-nominal letters) is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

    Cambridge is formed from a variety of institutions which include 31 constituent colleges and over 100 academic departments organised into six schools. The university occupies buildings throughout the town, many of which are of historical importance. The colleges are self-governing institutions founded as integral parts of the university. In the year ended 31 July 2014, the university had a total income of £1.51 billion, of which £371 million was from research grants and contracts. The central university and colleges have a combined endowment of around £4.9 billion, the largest of any university outside the United States. Cambridge is a member of many associations and forms part of the “golden triangle” of leading English universities and Cambridge University Health Partners, an academic health science centre. The university is closely linked with the development of the high-tech business cluster known as “Silicon Fen”.

     
  • richardmitnick 6:50 am on July 7, 2016 Permalink | Reply
    Tags: , , Black Holes, ,   

    From Stanford: “Stanford researchers help to explain how stars are born, cosmic structures evolve” 

    Stanford University Name
    Stanford University

    July 6, 2016
    Manuel Gnida

    An international team of scientists including Stanford researchers unveiled new findings on understanding the dynamic behavior of galaxy clusters and ties to cosmic evolution.

    Working with information sent from the Japanese Hitomi satellite, an international team of researchers that include Stanford scientists has obtained the first views of a supermassive black hole stirring hot gas at the heart of a galaxy cluster, like a spoon stirring cream into coffee.

    JAXA/Hitomi telescope

    2
    This image created by physicists at Stanford’s SLAC National Accelerator Laboratory illustrates how supermassive black holes at the center of galaxy clusters could heat intergalactic gas, preventing it from cooling and forming stars. (Image credit: SLAC National Accelerator Laboratory)

    These motions could explain why galaxy clusters form far fewer stars than expected – a puzzling property that affects the way cosmic structures evolve.

    The data, published today in Nature, were recorded with the X-ray satellite during its first month in space earlier this year, just before it spun out of control and disintegrated due to a chain of technical malfunctions.

    “Being able to measure gas motions is a major advance in understanding the dynamic behavior of galaxy clusters and its ties to cosmic evolution,” said study co-author Irina Zhuravleva, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC). “Although the Hitomi mission ended tragically after a very short period of time, it’s fair to say that it has opened a new chapter in X-ray astronomy.”

    KIPAC is a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

    Galaxy clusters, which consist of hundreds to thousands of individual galaxies held together by gravity, also contain large amounts of gas. Over time, the gas should cool down and clump together to form stars. Yet there is very little star formation in galaxy clusters, and until now scientists were not sure why.

    Norbert Werner, a research associate at KIPAC involved in the data analysis, said, “We already knew that supermassive black holes, which are found at the center of all galaxy clusters and are tens of billions of times more massive than the sun, could play a major role in keeping the gas from cooling by somehow injecting energy into it. Now we understand this mechanism better and see that there is just the right amount of stirring motion to produce enough heat.”

    Plasma bubbles stir

    About 15 percent of the mass of galaxy clusters is gas that is so hot – tens of millions of degrees Fahrenheit – that it shines in bright X-rays. In their study, the Hitomi researchers looked at the Perseus cluster, one of the most massive astronomical objects and the brightest in the X-ray sky.

    Other space missions before Hitomi, including NASA’s Chandra X-ray Observatory, had taken precise X-ray images of the Perseus cluster.

    3
    Perseus cluster. Chandra.

    These snapshots revealed how giant bubbles of ultra-hot, ionized gas, or plasma, rise from the central supermassive black hole as it catapults streams of particles tens of thousands of light-years into space.

    Additional images of visible light from the cluster showed streaks of cold gas that appear to get pulled away from the center of the galaxy. However, until now it has been unclear what effect the plasma bubbles have on this intergalactic gas.

    To find out, the researchers pointed one of Hitomi’s instruments – the soft X-ray spectrometer (SXS) – at the center of the Perseus cluster and analyzed its X-ray emissions.

    5
    Perseus cluster. Hitomi Collaboration / JAXA / NASA / ESA / SRON / CSA

    Steve Allen, a co-principal investigator and a professor of physics at Stanford and of particle physics and astrophysics at SLAC, said, “Since the SXS had 30 times better energy resolution than the instruments of previous missions, we were able to resolve details of the X-ray signals that weren’t accessible before. These new details resulted in the very first velocity map of the cluster center, showing the speed and turbulence of the hot gas.”

    By superimposing this map onto the other images, the researchers were able to link the observed motions to the plasma bubbles.

    Zhuravleva said, “From what we’ve seen in our data, the rising bubbles drag gas from the cluster center, which explains the filaments of stretched gas in the optical images. In this process, turbulence develops. In a way, the bubbles are like spoons that stir milk into a cup of coffee and cause eddies. The turbulence, in turn, heats the gas and suppresses star formation in the cluster.”

    Hitomi’s legacy

    Astrophysicists can use the new information to fine-tune models that describe how galaxy clusters change over time.

    One important factor in these models is the mass of galaxy clusters, which researchers typically calculate from the gas pressure in the cluster. However, motions cause additional pressure, and before this study it was unclear if the calculations need to be corrected for turbulent gas.

    “Although the motions heat the gas at the center of the Perseus cluster, their speed is only about 100 miles per second, which is surprisingly slow considering how disturbed the region looks in X-ray images,” said co-principal investigator Roger Blandford, the Luke Blossom Professor of Physics at Stanford and a professor of particle physics and astrophysics at SLAC. “One consequence is that corrections for these motions are only very small and don’t affect our mass calculations much.”

    Although the loss of Hitomi cut most of the planned science program short – it was supposed to run for at least three years – the researchers hope their results will convince the international community to plan another X-ray space mission.

    Werner said, “The data Hitomi sent back to Earth are just beautiful. They demonstrate what’s possible in the field and give us a taste of all the great science that should have come out of the mission over the years.”

    Hitomi is a joint project, with the Japan Aerospace Exploration Agency (JAXA) and NASA as the principal partners. Led by Japan, it is a large-scale international collaboration, boasting the participation of eight countries, including the United States, the Netherlands and Canada, with additional partnership by the European Space Agency (ESA). Other KIPAC researchers involved in the project are Tuneyoshi Kamae, Ashley King, Hirokazu Odaka and co-principal investigator Grzegorz Madejski.

    See the full article here .

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  • richardmitnick 6:59 am on July 6, 2016 Permalink | Reply
    Tags: , , Black Holes, ,   

    From RAS: “Earth-size telescope tracks the aftermath of a star being swallowed by a supermassive black hole” 

    Royal Astronomical Society

    Royal Astronomical Society

    05 July 2016
    Media contact

    Robert Cumming
    Communications Officer
    Onsala Space Observatory
    Chalmers University of Technology
    Sweden
    Tel: +46 70 493 3114 or +46 (0)31 772 5500
    robert.cumming@chalmers.se

    Science contact

    Jun Yang
    Onsala Space Observatory
    Chalmers University of Technology
    Sweden
    Tel: +46 (0)31 7725531
    jun.yang@chalmers.se

    Radio astronomers have used a radio telescope network the size of the Earth to zoom in on a unique phenomenon in a distant galaxy: a jet activated by a star being consumed by a supermassive black hole. The record-sharp observations reveal a compact and surprisingly slowly moving source of radio waves, with details published in a paper in the journal Monthly Notices of the Royal Astronomical Society. The results will also be presented at the European Week of Astronomy and Space Science in Athens, Greece, on Friday 8 July 2016.

    1
    This artist’s impression shows the remains of a star that came too close to a supermassive black hole. Extremely sharp observations of the event Swift J1644+57 with the radio telescope network EVN (European VLBI Network) have revealed a remarkably compact jet, shown here in yellow. Image credit: ESA/S. Komossa/Beabudai Design.

    The international team, led by Jun Yang (Onsala Space Observatory, Chalmers University of Technology, Sweden), studied the new-born jet in a source known as Swift J1644+57 with the European VLBI Network (EVN), an Earth-size radio telescope array.

    European VLBI
    European VLBI

    When a star moves close to a supermassive black hole it can be disrupted violently. About half of the gas in the star is drawn towards the black hole and forms a disc around it. During this process, large amounts of gravitational energy are converted into electromagnetic radiation, creating a bright source visible at many different wavelengths.

    One dramatic consequence is that some of the star’s material, stripped from the star and collected around the black hole, can be ejected in extremely narrow beams of particles at speeds approaching the speed of light. These so-called relativistic jets produce strong emission at radio wavelengths.

    The first known tidal disruption event that formed a relativistic jet was discovered in 2011 by the NASA satellite Swift. Initially identified by a bright flare in X-rays, the event was given the name Swift J1644+57. The source was traced to a distant galaxy, so far away that its light took around 3.9 billion years to reach Earth.

    Jun Yang and his colleagues used the technique of very long baseline interferometry (VLBI), where a network of detectors separated by thousands of kilometres are combined into a single observatory, to make extremely high-precision measurements of the jet from Swift J1644+57.

    2
    Three years of extremely precise EVN measurements of the jet from Swift J1644+5734 show a very compact source with no signs of motion. Lower panel: false colour contour image of the jet (the ellipse in the lower left corner shows the size of an unresolved source). Upper panel: position measurement with dates. One microarcsecond is one 3 600 000 000th part of a degree. Image credit: EVN/JIVE/J. Yang.

    “Using the EVN telescope network we were able to measure the jet’s position to a precision of 10 microarcseconds. That corresponds to the angular extent of a 2-Euro coin on the Moon as seen from Earth. These are some of the sharpest measurements ever made by radio telescopes”, says Jun Yang.

    Thanks to the amazing precision possible with the network of radio telescopes, the scientists were able to search for signs of motion in the jet, despite its huge distance.

    “We looked for motion close to the light speed in the jet, so-called superluminal motion. Over our three years of observations such movement should have been clearly detectable. But our images reveal instead very compact and steady emission – there is no apparent motion”, continues Jun Yang.

    The results give important insights into what happens when a star is destroyed by a supermassive black hole, but also how newly launched jets behave in a pristine environment. Zsolt Paragi, Head of User Support at the Joint Institute for VLBI ERIC (JIVE) in Dwingeloo, Netherlands, and member of the team, explains why the jet appears to be so compact and stationary.

    “Newly formed relativistic ejecta decelerate quickly as they interact with the interstellar medium in the galaxy. Besides, earlier studies suggest we may be seeing the jet at a very small angle. That could contribute to the apparent compactness”, he says.

    The record-sharp and extremely sensitive observations would not have been possible without the full power of the many radio telescopes of different sizes which together make up the EVN, explains Tao An from the Shanghai Astronomical Observatory, P.R. China.

    “While the largest radio telescopes in the network contribute to the great sensitivity, the larger field of view provided by telescopes like the 25-m radio telescopes in Sheshan and Nanshan (China), and in Onsala (Sweden) played a crucial role in the investigation, allowing us to simultaneously observe Swift J1644+57 and a faint reference source,” he says.

    Swift J1644+57 is one of the first tidal disruption events to be studied in detail, and it won’t be the last.

    “Observations with the next generation of radio telescopes will tell us more about what actually happens when a star is eaten by a black hole – and how powerful jets form and evolve right next to black holes”, explains Stefanie Komossa, astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany.

    “In the future, new, giant radio telescopes like FAST (Five hundred meter Aperture Spherical Telescope) and SKA (Square Kilometre Array) will allow us to make even more detailed observations of these extreme and exciting events,” concludes Jun Yang.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

     
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