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  • richardmitnick 11:13 am on May 5, 2016 Permalink | Reply
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    From ALMA: “ALMA Measures Mass of Black Hole with Extreme Precision” 

    ALMA Array

    ALMA

    05 May 2016

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

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

    Masaaki Hiramatsu

    Education and Public Outreach Officer, NAOJ Chile
    Observatory
Tokyo, Japan

    Tel: +81 422 34 3630

    E-mail: hiramatsu.masaaki@nao.ac.jp

    Richard Hook
    Public Information Officer, ESO

    Garching bei München, Germany

    Tel: +49 89 3200 6655

    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    1
    Combined image of NGC 1332 shows the central disk of gas surrounding the supermassive black hole at the center of the galaxy. New ALMA observations traced the motion of the disk, providing remarkably precise measurements of the black hole’s mass: 660 million times the mass of our Sun. The main image is from the Carnegie-Irvine Galaxy Survey. The box in the upper left is from the Hubble Space Telescope and shows the galaxy’s central region in infrared light and the dusty disk appears as a dark silhouette. The ALMA image, upper right box, shows the rotation of the disk, enabling astronomers to calculate its mass. The red region in the ALMA image represents emission that has been redshifted by gas rotating away from us; the blue represents blue-shifted gas rotating toward us. The range of colors represent rotational speeds up to 500 kilometers per second. Credit: A. Barth (UC Irvine), ALMA (NRAO/ESO/NAOJ); NASA/ESA Hubble; Carnegie-Irvine Galaxy Survey.

    3
    DSS image of lenticular galaxy NGC 1332 and part of elliptical galaxy NGC 1331. Celestial Atlas.

    Supermassive black holes, some weighing millions to billions of times the mass of the Sun, dominate the centers of their host galaxies. To determine the actual mass of a supermassive black hole, astronomers must measure the strength of its gravitational pull on the stars and clouds of gas that swarm around it.

    Using the Atacama Large Millimeter/submillimeter Array (ALMA), a team of astronomers has delved remarkably deep into the heart of a nearby elliptical galaxy to study the motion of a disk of cold interstellar gas encircling the supermassive black hole at its center. These observations provide one of the most accurate mass measurements to date for a black hole outside of our Galaxy, helping set the scale for these cosmic behemoths.

    To obtain this result, Aaron Barth, an astronomer at the University of California, Irvine (UCI), and lead author on a paper published* in the Astrophysical Journal Letters, and his team used ALMA to measure the speed of carbon monoxide gas in orbit around the black hole at the center of NGC 1332, a massive elliptical galaxy approximately 73 million light-years from Earth in the direction of the southern constellation Eridanus.

    “Measuring the mass of a black hole accurately is very challenging, even with the most powerful telescopes on Earth or in space,” Barth said. “ALMA has the revolutionary ability to observe disks of cold gas around supermassive black holes at small enough scales that we can clearly distinguish the black hole’s influence on the disk’s rotational speed.”

    The ALMA observations reveal details of the disk’s structure on the order of 16 light-years across. They also measure the disk’s rotation well within the estimated 80 light-year radius of the black hole’s “sphere of influence” – the region where the black hole’s gravity is dominant.

    Near the disk’s center, ALMA observed the gas traveling at more than 500 kilometers per second. By comparing these data with simulations, the astronomers calculated that the black hole at the center of NGC 1332 has a mass 660 million times greater than our Sun, plus or minus ten percent. This is about 150 times the mass of the black hole at the center of the Milky Way, yet still comparatively modest relative to the largest black holes known to exist, which can be many billions of solar masses.

    ALMA’s close-in observations were essential, the researchers note, to avoid confounding the black hole measurement with the gravitational influence of other material – stars, clouds of interstellar gas, and dark matter – that comprises most of the galaxy’s overall mass.

    “This black hole, though individually massive, accounts for less one percent of the mass of all the stars in the galaxy,” noted Barth. “Most of a galaxy’s mass is in the form of dark matter and stars, and on the scale of an entire galaxy, even a giant black hole is just a tiny speck in the center. The key to detecting the influence of the black hole is to observe orbital motion on such small scales that the black hole’s gravitational pull is the dominant force.” This observation is the first demonstration of this capability for ALMA.

    Astronomers use various techniques to measure the mass of black holes. All of them, however, rely on tracing the motion of objects as close to the black hole as possible. In the Milky Way, powerful ground-based telescopes using adaptive optics can image individual stars near the galactic center and precisely track their trajectories over time. Though remarkably accurate, this technique is feasible only within our own Galaxy; other galaxies are too distant to distinguish the motion of individual stars.

    To make similar measurements in other galaxies, astronomers either examine the aggregate motion of stars in a galaxy’s central region, or trace the motion of gas disks and mega-masers — natural cosmic radio sources.

    Previous studies of NGC 1332 with ground- and space-based telescopes gave wildly different estimates for the mass of this black hole, ranging from 500 million to 1.5 billion times the mass of the Sun.

    The new ALMA data confirm that the lower estimates are more accurate.

    Crucially, the new ALMA observations have higher resolution than any of the past observations. ALMA also detects the emission from the densest, coldest component of the disk, which is in a remarkably orderly circular motion around the black hole.

    Many past measurements made with optical telescopes, including the Hubble Space Telescope, focused on the emission from the hot, ionized gas orbiting in the central region of a galaxy. Ionized-gas disks tend to be much more turbulent than cold disks, which leads to lower precision when measuring a black hole’s mass.

    “ALMA can map out the rotation of gas disks in galaxy centers with even sharper resolution than the Hubble Space Telescope,” noted UCI graduate student Benjamin Boizelle, a co-author on the study. “This observation demonstrates a technique that can be applied to many other galaxies to measure the masses of supermassive black holes to remarkable precision.”

    Additional information

    These results were published* in the Astrophysical Journal Letters as Measurement of the black hole mass in NGC 1332 from ALMA observations at 0.044 arcsecond resolution, by Aaron Barth et al.

    The team is composed of Aaron Barth (University of California, Irvine), Benjamin D. Boizelle (University of California, Irvine), Jeremy Darling (University of Colorado, Boulder), Andrew J. Baker (Rutgers, the State University of New Jersey, Piscataway), David A. Buote (University of California, Irvine), Luis Ho (Kavli Institute of Astronomy and Astrophysics, Peking University, China), and Jonelle L. Walsh (Texas A&M University, College Station).

    See the full article here .

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

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

    NRAO Small

    ESO 50

    NAOJ

     
  • richardmitnick 7:06 pm on April 28, 2016 Permalink | Reply
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    From Nautilus: “Where Nature Hides the Darkest Mystery of All” 

    Nautilus

    Nautilus

    April 28, 2016
    Matthew Francis

    No known object in existence has as clear a division between “inside” and “outside” as a black hole. We live and see the outside, and no probe will bring us information about the inside. We can send radio messages or robotic spacecraft, but once they cross over into a black hole’s interior, we’ll never get back those emissaries … or any information about what happened to them.

    The boundary of a black hole is its event horizon. It’s not a surface in the usual sense—there’s no physical barrier—but it’s very much a real thing. Outside the horizon, an object can escape the black hole’s gravitational pull if it’s moving sufficiently fast; inside, it would need to move faster than light-speed, something forbidden by the laws of nature.

    In a meaningful sense, a black hole is its event horizon, since we can’t observe anything inside it by any method. The interior is nature’s biggest secret, enshrouded by a barrier that lets everything in but nothing out.

    1
    Simulating Space: A computer simulation of a gas cloud passing near the supermassive black hole at the center of the Milky Way, and the gravitational effects on the cloud. ESO/MPE/Marc Schartmann

    To make black holes even more enigmatic, they are also perfectly featureless, according to general relativity, our best explanation of how gravity works. They may be born from situations as different as the deaths of stars and the gravitational collapse of huge amounts of gas in the early universe, but the result is the same. Even the chemical composition of what gets sucked into and forms it is irrelevant. The only properties a black hole exhibits to the wider cosmos are its mass and how fast it’s rotating.

    This result is puckishly known as the “no-hair theorem”: Whatever is going on in the interior, no “hair” sticks out of the event horizon. (The name was coined by prominent physicist John Archibald Wheeler, obviously not a man sensitive about a receding hairline.) That theorem presents a challenging conundrum: We don’t know whether a black hole actually deletes its autobiography, “forgetting” its past and its progenitor’s composition, or preserves it somehow in a way we don’t know yet. If that information is destroyed, it’s a violation of one of the principles of quantum mechanics; if it’s preserved, it requires a theory beyond general relativity.

    The interior of a black hole isn’t merely an inaccessible region of the cosmos. It’s a laboratory for the most extreme physics: the strongest gravity and the most intense of quantum processes. For that reason, physicists are interested in understanding what goes on inside, even while they are frustrated by the lack of direct experiments or observations that could test their ideas.

    We can’t penetrate the bald event horizon, but that doesn’t mean we know nothing about a black hole’s interior. We’re pretty sure black holes don’t contain a portal to another region of space (a wormhole) or another reality, whatever sci-fi may have told us. Most physicists are also reasonably certain that a full description of the interior of black holes will require quantum gravity, a theory unifying quantum physics and general relativity—or possibly a modified version of our current model of gravity. The full structure of such a theory is unknown, but researchers have some thumbnail sketches about what it might look like.

    One hybrid approach was put together by Yakov Borisovich Zel’dovich, Jacob Bekenstein, and especially Stephen Hawking. Without a quantum theory of gravity, they used particle physics in combination with general relativity to show that the event horizon has a non-zero temperature and therefore glows, albeit very faintly. This glow is known as Hawking radiation; it arises when partnered particles—one electron and one positron, pairs of photons, etc.—are created in the intense gravitational field. One particle falls into the black hole, while the other escapes.

    Since the energy from the black hole was the source of the newly created particles’ mass (via E = mc2), the black hole’s mass shrinks slightly with every escaped particle. Unfortunately, the event horizon temperature is low for black holes like the ones we see, so Hawking radiation is correspondingly much fainter than other sources of light. However, if very low-mass black holes exist, they would shine brightly by Hawking radiation, and decay relatively quickly, evaporating away to nothing. Watching such a black hole vanish might help answer the question of whether information is truly lost or just hidden from us by the event horizon.

    Interestingly, Hawking himself thinks the problem has been solved, at least in principle: Black holes preserve the information they swallow, much as a hologram preserves information about three dimensions even though they are two-dimensional pictures. His hypothesis, based on an idea in string theory, doesn’t yet work in our four-dimensional cosmos (three spatial dimensions plus time), but rather for an abstract, higher-dimensional universe. As a result, not everyone is convinced by Hawking’s demonstration, even if they agree that black holes don’t forget their origins.

    Hawking radiation presumably consists of all sorts of things, including exotic particles like dark matter and gravitons, which we’ve never seen in the lab. That’s an intriguing notion, though again nature cruelly interferes with our best efforts to study it, by making tiny black holes rare or perhaps nonexistent. We might be able to see Hawking radiation from a larger black hole, but only if it’s not actively feeding on matter and if the hole is very close by. (Another option would be to create a tiny black hole in the lab, but without some new, exotic kind of physics, the necessary energy is beyond our reach.)

    The nearest known black hole to Earth, which carries the highly memorable name V404 Cygni, is about 8,000 light-years away. While that’s a mere hair’s breadth in cosmic terms, it’s far enough that we can’t study it up close. (For comparison, Voyager 1—the farthest human-built probe—is a little over 17 light-hours away at the time of writing.) The closest supermassive black hole (one that exceeds 100,000 times the mass of the sun) is even farther away: 26,000 light-years. That’s the monster at the center of the Milky Way, known as Sagittarius A* (pronounced “A star”).

    2
    V404 CYGNI, DSS Ultracam

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

    We see black holes like V404 Cygni by the matter surrounding them: Material stripped off companion stars, for example, heats up as it orbits the black hole, emitting strong X-ray and radio radiation. Thanks to high-resolution observations made last year, astronomers have measured swirling gas at very close orbits to the giant black hole in the galaxy M87. And the dance of stars and plasma near Sagittarius A* reveals the presence of the black hole that helps keep our galaxy together.

    With continued improvements, we’ll be able to get an even better view of black holes, drawing ever closer to the event horizon. Yet nature still hides the mystery of what lies inside a black hole, perhaps forever.

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 12:48 pm on April 26, 2016 Permalink | Reply
    Tags: , Black Holes,   

    From Science Alert: “Physicists have created a ‘black hole’ in the lab that could finally prove Hawking radiation exists” 

    ScienceAlert

    Science Alert

    26 APR 2016
    BEC CREW

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

    1
    Alain r/Wikimedia

    Will Stephen Hawking get his Nobel prize?

    Some 42 years ago, renowned theoretical physicist Stephen Hawking proposed that not everything that comes in contact with a black hole succumbs to its unfathomable nothingness. Tiny particles of light (photons) are sometimes ejected back out, robbing the black hole of an infinitesimal amount of energy, and this gradual loss of mass over time means every black hole eventually evaporates out of existence.

    Known as Hawking radiation, these escaping particles help us make sense of one of the greatest enigmas in the known Universe, but after more than four decades, no one’s been able to actually prove they exist, and Hawking’s proposal remained firmly in hypothesis territory.

    But all that could be about to change, with two independent groups of researchers reporting that they’ve found evidence to back up Hawking’s claims, and it could see one of the greatest living physicists finally win a Nobel Prize.

    So let’s go back to 1974, when all of this began. Hawking had gotten into an argument with Princeton University graduate student, Jacob Bekenstein, who suggested in his PhD thesis that a black hole’s entropy – the ‘disorder’ of a system, related to its volume, energy, pressure, and temperature – was proportional to the area of its event horizon.

    As Dennis Overbye explains for The New York Times, this was a problem, because according to the accepted understanding of physical laws at the time – including Hawking’s own work – the entropy and the volume of a black hole could never decrease.

    Hawking investigated the claims, and soon enough, realised that he had been proven wrong. “[D]r Hawking did a prodigious calculation including quantum theory, the strange rules that govern the subatomic world, and was shocked to find particles coming away from the black hole, indicating that it was not so black after all,” Overbye writes.

    Hawking proposed that the Universe is filled with ‘virtual particles’ that, according to what we know about how quantum mechanics works, blink in and out of existence and annihilate each other as soon as they come in contact – except if they happen to appear on either side of a black hole’s event horizon. Basically, one particle gets swallowed up by the black hole, and the other radiates away into space.

    The existence of Hawking radiation has answered a lot of questions about how black holes actually work, but in the process, raised a bunch of problems that physicists are still trying to reconcile.

    “No result in theoretical physics has been more fundamental or influential than his discovery that black holes have entropy proportional to their surface area,” says Lee Smolin, a theoretical physicist from the Perimeter Institute for Theoretical Physics in Canada.

    While Bekenstein received the Wolf Prize in 2012 and the American Physical Society’s Einstein prize in 2015 for his work, which The New York Times says are often precursors to the Nobel Prize, neither scientist has been awarded the most prestigious prize in science for the discovery. Bekenstein passed away last year, but Hawking is now closer than ever to seeing his hypothesis proven.

    The problem? Remember when I said the escaping photons were stealing an infinitesimal amount of energy from a black hole every time they escaped? Well, unfortunately for Hawking, this radiation is so delicate, it’s practically impossible to detect it from thousands of light-years away.

    But physicist Jeff Steinhauer from Technion University in Haifa, Israel, thinks he’s come up with a solution – if we can’t detect Hawking radiation in actual black holes thousands of light-years away from our best instruments, why not bring the black holes to our best instruments?

    As Oliver Moody reports for The Times, Steinhauer has managed to created a lab-sized ‘black hole’ made from sound, and when he kicked it into gear, he witnessed particles steal energy from its fringes.

    Reporting his experiment in a paper* posted to the physics pre-press website, arXiv.org, Steinhauer says he cooled helium to just above absolute zero, then churned it up so fast, it formed a ‘barrier’ through which sound should not be able to pass.

    “Steinhauer said he had found signs that phonons, the very small packets of energy that make up sound waves, were leaking out of his sonic black hole just as Hawking’s equations predict they should,” Moody reports.

    To be clear, the results of this experiment have not yet been peer-reviewed – that’s the point of putting everything up for the public to see on arXiv.org. They’re now being mulled over by physicists around the world, and they’re already proving controversial, but worthy of further investigation.

    “The experiments are beautiful,” physicist Silke Weinfurtner from the University of Nottingham in the UK, who is running his own Earth-based experiments to try and detect Hawking radiation, told The Telegraph. “Jeff has done an amazing job, but some of the claims he makes are open to debate. This is worth discussing.”

    Meanwhile, a paper published** in Physical Review Letters last month has found another way to strengthen the case for Hawking radiation. Physicists Chris Adami and Kamil Bradler from the University of Ottawa describe a new technique that allows them to follow a black hole’s life over time.

    That’s exciting stuff, because it means that whatever information or matter that passes over the event horizon doesn’t ‘disappear’ but is slowly leaking back out during the later stages of the black hole’s evaporation.

    “To perform this calculation, we had to guess how a black hole interacts with the Hawking radiation field that surrounds it,” Adami said in a press release. “This is because there currently is no theory of quantum gravity that could suggest such an interaction. However, it appears we made a well-educated guess because our model is equivalent to Hawking’s theory in the limit of fixed, unchanging black holes.”

    Both results will now need to be confirmed, but they suggest that we’re inching closer to figuring out a solution for how we can confirm or disprove the existence of Hawking radiation, and that’s good news for its namesake.

    As Moody points out, Peter Higgs, who predicted the existence of the Higgs boson, had to wait 49 years for his Nobel prize, we’ll have to wait and see if Hawking ends up with his own.

    *Science paper:
    Observation of thermal Hawking radiation and its entanglement in an analogue black hole

    **Science Paper:
    One-Shot Decoupling and Page Curves from a Dynamical Model for Black Hole Evaporation

    See the full article here .

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  • richardmitnick 12:58 pm on April 14, 2016 Permalink | Reply
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    From phys.org: “The hot problem of black hole firewalls” 

    physdotorg
    phys.org

    April 14, 2016
    Ross Lockwood

    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital
    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital

    For the last four years, physicists studying the mathematical underpinnings of black holes have been wrestling with a strange idea: that black holes contain a region known as a “firewall,” which utterly annihilates matter that dares to cross its boundaries. However, a new paper titled Naked Black Hole Firewalls*, co-authored by University of Alberta physics professor Don N. Page, aims to attack the fundamental tenets that give rise to this strange idea—with something much stranger.

    “The putative black hole firewall is one of the hottest problems in physics today, and we hope that our paper makes a significant contribution to the field,” says Page. “As part of the University of Alberta community, I’ve been privileged to be able to interact with many others in this field around the world.”

    Page’s contributors include Pisin Chen of the National Taiwan University and Stanford University, Yen Chin Ong of the Nordic Institute for Theoretical Physics (Nordita), Misao Sasaki of Kyoto University and Dong-han Yeom of the National Taiwan University.

    The classic picture of a black hole comes directly from Einstein’s theory of general relativity: a massive object warps the fabric of spacetime and, given sufficient material, this region of spacetime becomes so steep that not even light has sufficient speed to escape. Because no light can escape, these objects became known as black holes, entering our cultural consciousness as the universe’s most terrifying garbage disposals. A hapless space traveller entering the black hole’s event horizon, according to this model, would be completely destroyed inside the black hole.

    Despite their apparent simplicity, however, black holes have been devilishly difficult to describe, and in the 1970s, physicist Stephen Hawking proposed that some particles could in fact escape from a black hole through a process involving the creation of entangled particles, in a theory now known as Hawking radiation. Since then, the field of black hole physics has been a wellspring of interesting phenomena, requiring the mathematics of both quantum theory and general relativity for a complete description.

    In the intervening four decades, an outstanding problem—the black hole information paradox—has continued to stymie physicists as a direct result of introducing the mathematics of quantum theory into the mix. “At first, most scientists working on Einstein’s theory of gravity thought Hawking’s original suggestion was right, that information is lost when black holes form and evaporate,” says Page, who wrote the first paper objecting to Hawking’s suggestion. “Now most, though not all, gravitational physicists, including Hawking himself, believe that information is not lost. However, it is still mysterious how the information is preserved in detail.”

    In quantum mechanics, the two principles of quantum determinism and reversibility suggest that information must always be preserved. But since material falling into a black hole—along with the information describing that material—are apparently annihilated sometime after they cross the event horizon, physicists have been left scratching their heads about this seeming inconsistency.

    The paradox itself arises due to Hawking radiation, which demonstrates that matter can be emitted from a black hole, but initially it appeared that no information about the matter that once fell into the black hole is carried away. In 2012, a group of physicists studying this paradox found that three basic assumptions involved in this paradox cannot all be consistent.

    Namely, principles of unitarity and local quantum field theory contradicted the assumption of “no-drama”—meaning that nothing unusual should happen when an object falls through the event horizon. Instead, they proposed that the most conservative solution to this contradiction is that there would indeed be “drama” at the surface of the black hole in the form of a “firewall” that would destroy an infalling object. This seems rather surprising, because the curvature is negligibly small at the event horizon of a sufficiently large black hole, where general relativity should hold and one would expect nothing special when crossing the horizon.

    “So-called firewalls, or high-energy density regions that we would otherwise think of as the surface of the black hole, would destroy anything falling in,” explains collaborator Pisin Chen at the National Taiwan University.

    The putative position of the firewall is something that didn’t sit well with the authors of the paper, who began work on this project at a workshop at the Yukawa Institute for Theoretical Physics in Kyoto, Japan. Since the firewall was proposed to be hidden behind the event horizon, an observer travelling past the gently curved event horizon of a large black hole, hoping to glimpse its interior, would instead be instantly incinerated the moment they passed behind the veil. Attacking the fundamental tenets used to create the firewall, the authors demonstrate that this region of quantum-mechanical destruction can strangely migrate to a region outside of the black hole due to the quantum fluctuations of the Hawking radiation, allowing an observer a full-frontal view of a black hole’s “naked firewall.”

    “If a firewall exists, not only would an infalling object be destroyed by it, but the destruction could be visible, even from the outside,” says Misao Sasaki, a contributor from Kyoto University.

    Page emphasizes that such a “naked firewall” outside of the event horizon is problematic. If a firewall actually exists, the authors argue that it wouldn’t simply be confined to a region within the black hole, but its destructive power could reach beyond the limits of the event horizon, into a region of space that could be observed. This makes the notion of firewalls less conservative than previously thought, and suggests putting more effort into finding a better solution to the firewall paradox.

    Science paper
    *Naked Black Hole Firewalls.
    Science team:
    Pisin Chen, 1,2; Yen Chin Ong, 3 y; Don N. Page, 4, z; Misao Sasaki, 5, x; and Dong-han Yeom, 1

    Affiliations
    1 Leung Center for Cosmology and Particle Astrophysics,
    National Taiwan University, Taipei 10617, Taiwan
    2 Kavli Institute for Particle Astrophysics and Cosmology,
    SLAC National Accelerator Laboratory,
    Stanford University, CA 94305, U.S.A.
    3 Nordita, KTH Royal Institute of Technology & Stockholm University,
    Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden
    4 Theoretical Physics Institute, University of Alberta,
    Edmonton, Alberta T6G 2E1, Canada
    5 Yukawa Institute for Theoretical Physics,
    Kyoto University, Kyoto 606-8502, Japan

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 9:38 am on April 14, 2016 Permalink | Reply
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    From Science Alert: “Astronomers have discovered a region in space where black holes have mysteriously aligned” 

    ScienceAlert

    Science Alert

    12 APR 2016
    BEC CREW

    1

    What the hell’s going on out there?

    There’s a region in the distant Universe where a handful of supermassive black holes have mysteriously aligned, and as a result, they’re spewing out incredibly powerful radio jets in the same direction. This is the first time astronomers have seen such a phenomenon, and they say it could be the result of fluctuations of primordial mass that appeared in the early Universe.

    “Since these black holes don’t know about each other, or have any way of exchanging information or influencing each other directly over such vast scales, this spin alignment must have occurred during the formation of the galaxies in the early Universe,” explains one of the team, Andrew Russ Taylor, director of South Africa’s Institute for Data Intensive Astronomy.

    As with many discoveries that happen in outer space, no one was expecting to find a region where supermassive black holes had mysteriously managed to sync up their spins.

    Taylor and his team were actually on the hunt for the faintest radio sources in the Universe, using data from the Giant Metrewave Radio Telescope (GMRT) in India – one of the largest and most sensitive radio telescope arrays in the world.

    Giant Metrewave Radio Telescope near Pune in India
    Giant Metrewave Radio Telescope near Pune in India

    The GMRT had just completed a three-year deep radio imaging survey, detecting radio waves spewed forth by black holes in a distant region of the Universe called ELAIS, which encompasses several galaxies.

    By looking at the direction these radio waves were coming from, the researchers figured out that within ELAIS-N1, the supermassive black holes at the centre of each of these galaxies were all spinning in the same direction. But how?

    Taylor and his colleagues suggest that the black holes are too far apart to have influenced each other’s alignment in their current positions in space, so whatever forced them into the same spin must happened very early on in the formation of the Universe.

    “[T]he alignment of the black holes is probably caused by an overall spin in the structure of this region of space, triggered by fluctuations of primordial matter in the early Universe, way before galaxies even formed,” Yasmin Tayag reports for Inverse.

    But if we accept that, then something even greater must have given rise to the fluctuations of primordial matter that caused these supermassive black holes to align. In other words, what caused the fluctuations that forced these black holes into the same spin?

    It’s not yet clear, and a large-scale spin distribution has not been predicted by our current understanding of the physics that govern the Universe, but the researchers suggest that it could be anything from incredibly strong cosmic magnetic fields – possibly associated with exotic particles such as axions – to something called cosmic strings, which are theoretical fault lines in the Universe that exist between different regions of space.

    “This is not obviously expected based on our current understanding of cosmology. It’s a bizarre finding,” astronomer Romeel Dave from the University of Western Cape in South Africa, who was not involved in the discovery, said in a press statement.

    We’re going to need much more sensitive telescopes to figure that out, and with the South African MeerKAT radio telescope and the Square Kilometre Array (SKA) – the world’s most powerful radio telescope and one of the biggest scientific instruments ever devised – currently under construction, we might not have to wait too long.

    SKA Meerkat telescope
    SKA Meerkat telescope

    “[We really need MeerKAT to make the very sensitive maps, over a very large area and with great detail, that will be necessary to differentiate between possible explanations,” says Taylor. “It opens up a whole new research area for these instruments, which will probe as deeply into the and as far back as we can go – it’s going to be an exciting time to be an astronomer.”

    The discovery has been reported* in the Monthly Notices of the Royal Astronomical Society.

    *Science paper:
    Alignments of radio galaxies in deep radio imaging of ELAIS N1

    Science team:
    A. R. Taylor 1,2,★ and P. Jagannathan 1,3

    Affiliations:
    1 Department of Astronomy, University of Cape Town, Rondebosch 7701, South Africa
    2 Department of Physic and Astronomy, University of the Western Cape, Bellville 7535, South Africa
    3 National Radio Astronomy Observatory, Socorro, NM, USA

    See the full article here .

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  • richardmitnick 4:50 pm on April 8, 2016 Permalink | Reply
    Tags: , Black Holes, ,   

    From New Scientist: “Physics adventures down the superfluid supersonic black hole” 

    NewScientist

    New Scientist

    9 April 2016
    Anil Ananthaswamy

    1
    What happens to the stuff a black hole sucks in? Jan Kornstaedt/Gallerystock

    IMAGINE lying in a giant bathtub when someone pulls the plug. Sliding towards a watery exit from this world, it gets worse. The fluid gathers pace to supersonic speed and you realise no one can even hear you scream. Your sounds are transported with you down the drain, lost to the bathtub for all time.

    It is the stuff of surrealist nightmares – and a pretty fair description of what happens to an atom or a photon of light as it crosses a black hole’s event horizon. Black holes famously devour anything that comes too close: light, matter, information. In doing so, they cause some almighty headaches for our best theories of physical reality.

    Or do they? Although we are pretty certain black holes exist, we’ve never observed one directly, let alone got up close and personal. That’s where the bathtub analogy is now coming into serious play. Get fully to grips with it, and we could have a new way not just to fathom black holes, but also to crack some of cosmology’s other toughest nuts – from why the expansion of the universe is accelerating to how it all began.

    There’s a catch, naturally. To make the analogy real, we can’t use any old water from the tap. It takes a fluid so extreme and bizarre that it was fabricated for the first time just 20 years ago, and only exists within a whisker of absolute zero, the lowest temperature there is. With that magic ingredient, you can begin to make a superfluid sonic black hole.

    Black holes are the most mysterious of the many predictions made by general relativity, Einstein’s theory of gravity that he formulated just over a century ago. General relativity is a peerless guide to the workings of gravity, but puts gravity at odds with the other known forces of nature. Unlike them, gravity is not caused by the exchange of quantum particles; instead, massive bodies bend space and time around them, creating dents in the fabric of the universe that dictate how other bodies move.

    The world according to general relativity contains some shady spectres – invisible dark matter to explain why galaxies whirl at the speeds they do, and dark energy to explain why the expansion of the universe is accelerating. The theory also fails completely when you wind the universe back to its first instants and the big bang. Here, it predicts a seemingly nonsensical “singularity” of infinite temperature and density.

    Still, black holes take the biscuit. We now think these impossibly dense scrunchings of mass exist across the cosmos – where massive stars have collapsed in on themselves, and at the heart of galaxies including our own.

    For all their heft, however, black holes seem strangely tenuous, at least in theory. In 1974, physicist Stephen Hawking used quantum rules to show that all black holes must eventually evaporate, apparently destroying any information they might have swallowed, a physical no-no.

    According to quantum physics, space-time is a roiling broth of particles and their antiparticles that pop up spontaneously in pairs, disappearing again almost instantaneously. But when such a pair pops up at the edge of a black hole’s event horizon – the point beyond which nothing can escape its gravity – sometimes one will have the energy to whizz away, while the other falls in. By the law of conservation of energy, this second particle must have negative energy, causing the black hole to slowly lose its oomph and evaporate. The signal this is happening is a faint stream of escaping partner particles – Hawking radiation.

    In theory at least, Hawking radiation has a temperature: the smaller the black hole, the warmer it is. For a black hole 30 times the mass of our sun, it is a titchy nanokelvin or so, impossible to measure in the chaotic surroundings of an astrophysical black hole. Hopes were high that the Large Hadron Collider at CERN near Geneva, Switzerland, might produce mini black holes with measurable Hawking radiation – but not a peep.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    CERN/LHC

    “This is a pity, because if they had, I would have got a Nobel prize,” Hawking said in a BBC lecture this February.

    2
    Bose-Einstein condensates arise when supercooled gases of atoms all enter the same quantum state. Pascal Goetgheluck/Science Photo Library

    Wind back to 1981, however, and physicist William Unruh of the University of British Columbia in Vancouver, Canada, was thinking of ways to study Hawking radiation. It led him to some strange parallels between the “metric” – a mathematical construction in general relativity that expresses the geometry of space-time – and equations used to describe superfluid flow.

    Unruh showed that the equations governing such flow at supersonic speed mimicked the metric of space-time around a black hole. This implied a superfluid could create a black hole that would trap “phonons” of sound, just as an astrophysical black hole traps photons of light. It’s the surrealist nightmare, with an added twist. Just as with an astrophysical black hole, quantum fluctuations would make a sonic black hole emit Hawking radiation – but made of phonons, not photons.

    Unruh realised this could be just the thing to test Hawking’s idea. Prove the radiation exists in one situation, and the mathematical mirror provides a pretty good indication that it does in the other.

    He was rather ahead of the times. Although the first superfluid state was created in liquid helium in the late 1930s, for a sonic black hole the fluid had to be flowing faster than the speed of sound in that fluid – in superfluid helium, that’s hundreds of metres a second. Experimental verification of Unruh’s idea would have to wait.

    Then, in 1995, came a Nobel-prizewinning development: the creation of the first Bose-Einstein condensates (BECs). This is an entirely different state of matter beyond solid, liquid and gas, made up of collections of atoms cooled down to temperatures so low, sometimes a few nanokelvin above absolute zero, that the individual atoms lose their identity. They occupy the same quantum state, and behave and flow as one.

    Sonic event horizon

    Creating this extreme, bizarre form of superfluid was an experimental tour de force, and came with an important detail as far as the black hole story was concerned: in a BEC, the speed of sound is just millimetres a second. Sonic black holes suddenly looked feasible.

    Iacopo Carusotto, a theorist at the BEC Center in Trento, Italy, was initially a sceptic. But returning from holiday in 2005, he found himself sitting next to a college friend on a train who turned out to be a gravitational physicist, and the two got talking shop. The friend introduced Carusotto to Roberto Balbinot, an expert on general relativity at the University of Bologna. These two started to build computer models of sonic black holes that took into account factors such as how the speed of sound varies according to how a fluid is moving, its temperature, the wavelength of the phonons and so on.

    Carusotto still has the first image spewed out by the simulation in 2008 hanging on the wall in his office. “I jumped off my chair,” he says. It shows that as a Bose-Einstein condensate starts flowing at supersonic speeds, a sonic event horizon forms and phonons of Hawking radiation spontaneously appear. “To see it so precisely in agreement with theory was a great surprise, and a great success,” says Carusotto.

    Jeff Steinhauer, an atomic physicist at the Technion-Israel Institute of Technology in Haifa, was the man who could make the analogy an experimental reality. He had developed some crucial tools: a way of measuring a condensate’s temperature to an accuracy of a nanokelvin, and complex systems of adjustable magnetic fields to stop condensates sagging and being disrupted under the effect of real gravity. By 2009, he was able to use lasers to accelerate a long, thin stretch of condensate to supersonic speed. The result was the first sonic black hole with an event horizon (Physical Review Letters*, vol 105, p 240401).

    Measuring individual phonons to verify the existence of Hawking radiation proved more tricky. In 2014, Steinhauer reached a halfway house by accelerating a thin condensate stream to supersonic speed and then allowing it to slow again. This created the equivalent of two event horizons – a black-hole horizon from which no sound could escape, and a “white-hole” horizon into which no sound could enter. In such a situation, Hawking phonons produced by the black hole bounce between the two horizons, producing more and more Hawking radiation in a similar way to how light is amplified in a laser.

    3
    Bose-Einstein condensates may hold the answer. National Institute of Syandards and ethnology/Science Photo Library

    And amplified radiation is certainly what Steinhauer saw. “It was very exciting to suddenly see this effect,” he says. “It was very gratifying to think that the physics Hawking predicted was creating it.” The question raised by Carusotto and others since is how to tell for certain whether the initial phonon was created by spontaneous, random quantum fluctuation rather than some classical process. Final confirmation could be coming soon: Steinhauer currently has a paper** under peer review in which he reports seeing unadorned Hawking radiation from a single sonic horizon (arxiv.org/abs/1510.00621).

    Steinhauer himself wouldn’t discuss this work further, but theorist Stefano Liberati of the International School for Advanced Studies in Trieste, Italy, is excited. “If this result is confirmed, it’s definitely a major breakthrough,” he says. “It would be the first experimental detection of Hawking radiation.”

    Whether it’s enough for Hawking to get his Nobel prize remains to be seen, but Liberati thinks this work is just the beginning. Not only might sonic black holes illuminate further mysteries of the real thing (see “What are black holes made of?“), but get superfluids flowing in different ways and you can create other space-time geometries that equate to other cosmological problems. One is the exponential expansion of the universe in the period known as inflation, thought to have occurred immediately after the big bang. Current cosmological theories predict that during this phase, the quantum fluctuations of space-time also got stretched, eventually giving rise to the particles we see everywhere today. We can’t test this idea directly, but Liberati and his colleagues have shown how a similar situation implemented using a condensate should give rise to phonons. “You should be able to reproduce the salient features of cosmological particle creation,” he says.

    One way of doing this involves using lasers or magnetic fields to suddenly compress a condensate, thus changing the speed of sound within it. This creates an analogy to the change in light’s travel time between two points in space as the universe expands. In 2012, Christoph Westbrook and his colleagues at the Charles Fabry Laboratory at the University of Paris-Sud in France did just that and saw indirect effects of phonon creation – although the experimental temperature of 200 nanokelvin was still too high to rule out thermal fluctuations as the source.

    Liberati suggests that a similar analogy could provide clues to another huge cosmological conundrum, dark energy. The peculiar problem of dark energy is not so much that it exists. General relativity allows for a “cosmological constant” that represents the energy of empty space and whose effect would be to expand space ever faster, just as dark energy is thought to do. But calculating the value of this constant from observations gives a number 10120 times smaller than the value you get from quantum field theory.

    Again, Bose-Einstein condensates could hold the answer. In a condensate, not all the atoms that you cool down end up in the lowest-energy condensate state: you never get a perfect condensate. What’s more, these stragglers “backreact” with the condensate, an interaction that appears in the equations in a similar way to the cosmological constant.

    “The superfluid analogy might provide clues to the cosmic conundrum of dark energy“

    To Liberati, this is suggestive of the real nature of dark energy, and space-time itself. What if the fabric of the universe, and hence gravity, emerge from some as-yet-unknown “atoms” of space-time, just as a superfluid state emerges from normal atoms when they are cooled? If some of these atoms are left over and do not form the basis of space-time, then their backreaction with those that do could reduce the value of the cosmological constant to match what astronomers find.

    In this view, the equations of general relativity might just be a high-level picture that emerges from a more fundamental description. In fluid dynamics, the set of equations known as Euler’s equations similarly describes the flow as a whole, but not the molecular interactions that underlie it. “It’s teaching you a very important lesson,” says Liberati. “If gravity is emergent, the only way you can calculate the cosmological constant is by knowing the fundamental system from which gravity emerges.”

    The quest for a more fundamental picture of gravity is central to the search for a “theory of everything” that will finally unite all the forces of nature, gravity included. So far, convincing answers have been thin on the ground – in part because we have lacked any way to test ideas experimentally. In that sense, listening carefully to sounds swirling through superfluids could be the stuff of physicists’ dreams, rather than their nightmares. “It’s a success story,” says Liberati. “It’s a case in which theoretical physics finally made connection with experiments.”

    _____________________________________________________________________________________________

    What are black holes made of?

    For all we know, it could be snails and puppy-dog tails. There is no microscopic theory of a black hole’s innards, but Georgi Dvali of the Ludwig Maximilian University of Munich, Germany, thinks we might find clues in parallels between how black holes and Bose-Einstein condensates process information.

    Black holes are careless stewards of information, apparently dribbling it away as they evaporate (see main story), but they are efficient stores of it. It would take about 10-5 electronvolts of energy to stuff one quantum bit of information into a cubic-centimetre box. To stuff that qubit into a black hole of the same size – which would have the mass of Earth – would take 1066 times less energy, says Dvali.

    Intriguingly, Dvali and his colleagues have shown that Bose-Einstein condensates seem to process information similarly to black holes. “There is a one-to-one correspondence,” he says. “In particular, the system delivers very cheap qubits for storing information.”

    Bose-Einstein condensates exist in a so-called quantum-critical state, transitioning from a normal state to one in which all the atoms act as a coherent quantum whole. Dvali speculates that the parallels indicate that black holes are quantum-critical states too – albeit not of atoms, but of quantum particles of gravity known as gravitons.

    _____________________________________________________________________________________________

    *Realization of a sonic black hole analogue in a Bose-Einstein condensate
    Oren Lahav, Amir Itah, Alex Blumkin, Carmit Gordon, Shahar Rinott,
    Alona Zayats, and Jeff Steinhauer
    Technion – Israel Institute of Technology, Haifa, Israel

    **Observation of thermal Hawking radiation and its entanglement in an analogue black hole
    Jeff Steinhauer
    Department of Physics, Technion—Israel Institute of Technology, Technion City, Haifa 32000, Israel

    See the full article here .

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  • richardmitnick 3:31 pm on April 6, 2016 Permalink | Reply
    Tags: , , Black Holes,   

    From Hubble: “Behemoth Black Hole Found in an Unlikely Place” 

    NASA Hubble Banner

    NASA Hubble Telescope

    Hubble

    April 6, 2016
    Donna Weaver / Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4493 / 410-338-4514
    dweaver@stsci.edu / villard@stsci.edu

    Chung-Pei Ma
    University of California, Berkeley, California
    510-301-3780
    cpma@berkeley.edu

    Jens Thomas
    Max Planck Institute for Extraterrestrial Physics, Garching, Germany
    011-49-89-3000-3714
    jthomas@mpe.mpg.de

    1

    2

    Credit: NASA, ESA, C.-P. Ma (University of California, Berkeley), and J. Thomas (Max Planck Institute for Extraterrestrial Physics, Garching, Germany)
    Release Date: April 6, 2016

    3

    Fast Facts:
    Data Description: The HST data were taken from proposal 7886 PI: A. Quillen (University of Rochester), G. Bower (CSC/STScI), and G. Rieke (Steward Observatory/University of Arizona). The science team comprises J. Thomas (Max Planck Institute for Extraterrestrial Physics, Garching, Germany), C.-P. Ma (University of California, Berkeley), N. McConnell (Dominion Astrophysical Observatory), J. Greene (Princeton University), J. Blakeslee (Dominion Astrophysical Observatory), and R. Janish (University of California, Berkeley).
    Instrument: NICMOS
    Exposure Date: November 10, 1998

    Science paper

    Astronomers have uncovered a near-record-breaking supermassive black hole, weighing 17 billion suns, in an unlikely place: in the center of a galaxy in a sparsely populated area of the universe. The observations, made by NASA’s Hubble Space Telescope and the Gemini telescope in Hawaii, could indicate that these monster objects may be more common than once thought.

    Gemini/North telescope
    Gemini North Interior
    Gemini/North telescope

    Until now, the biggest supermassive black holes — those roughly 10 billion times the mass of our sun — have been found at the cores of very large galaxies in regions of the universe packed with other large galaxies. In fact, the current record holder tips the scale at 21 billion suns and resides in the crowded Coma galaxy cluster, which consists of over 1,000 galaxies.

    Coma cluster
    Coma cluster. Hubble

    “The newly discovered supersized black hole resides in the center of a massive elliptical galaxy, NGC 1600, located in a cosmic backwater, a small grouping of 20 or so galaxies,” said lead discoverer Chung-Pei Ma, a University of California-Berkeley astronomer and head of the MASSIVE Survey, a study of the most massive galaxies and supermassive black holes in the local universe. While finding a gigantic black hole in a massive galaxy in a crowded area of the universe is to be expected — like running across a skyscraper in Manhattan — it seemed less likely they could be found in the universe’s small towns.

    4
    Image: NGC 1600 – DSS

    “There are quite a few galaxies the size of NGC 1600 that reside in average-size galaxy groups,” Ma said. “We estimate that these smaller groups are about 50 times more abundant than spectacular galaxy clusters like the Coma cluster. So the question now is, ‘Is this the tip of an iceberg?’ Maybe there are more monster black holes out there that don’t live in a skyscraper in Manhattan, but in a tall building somewhere in the Midwestern plains.”

    The researchers also were surprised to discover that the black hole is 10 times more massive than they had predicted for a galaxy of this mass. Based on previous Hubble surveys of black holes, astronomers had developed a correlation between a black hole’s mass and the mass of its host galaxy’s central bulge of stars — the larger the galaxy bulge, the proportionally more massive the black hole. But for galaxy NGC 1600, the giant black hole’s mass far overshadows the mass of its relatively sparse bulge. “It appears that that relation does not work very well with extremely massive black holes; they are a larger fraction of the host galaxy’s mass,” Ma said.

    Ma and her colleagues are reporting the discovery of the black hole, which is located about 200 million light-years from Earth in the direction of the constellation Eridanus, in the April 6 issue of the journal Nature. Jens Thomas of the Max Planck Institute for Extraterrestrial Physics, Garching, Germany, is the paper’s lead author.

    One idea to explain the black hole’s monster size is that it merged with another black hole long ago when galaxy interactions were more frequent. When two galaxies merge, their central black holes settle into the core of the new galaxy and orbit each other. Stars falling near the binary black hole, depending on their speed and trajectory, can actually rob momentum from the whirling pair and pick up enough velocity to escape from the galaxy’s core. This gravitational interaction causes the black holes to slowly move closer together, eventually merging to form an even larger black hole. The supermassive black hole then continues to grow by gobbling up gas funneled to the core by galaxy collisions. “To become this massive, the black hole would have had a very voracious phase during which it devoured lots of gas,” Ma said.

    The frequent meals consumed by NGC 1600 may also be the reason why the galaxy resides in a small town, with few galactic neighbors. NGC 1600 is the most dominant galaxy in its galactic group, at least three times brighter than its neighbors. “Other groups like this rarely have such a large luminosity gap between the brightest and the second brightest galaxies,” Ma said.

    Most of the galaxy’s gas was consumed long ago when the black hole blazed as a brilliant quasar from material streaming into it that was heated into a glowing plasma.

    Quasar. ESO/M. Kornmesser
    Quasar. ESO/M. Kornmesser

    “Now, the black hole is a sleeping giant,” Ma said. “The only way we found it was by measuring the velocities of stars near it, which are strongly influenced by the gravity of the black hole. The velocity measurements give us an estimate of the black hole’s mass.”

    The velocity measurements were made by the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North 8-meter telescope on Mauna Kea in Hawaii.

    GEMINI/North GMOS
    GEMINI/North GMOS

    GMOS spectroscopically dissected the light from the galaxy’s center, revealing stars within 3,000 light-years of the core. Some of these stars are circling around the black hole and avoiding close encounters. However, stars moving on a straighter path away from the core suggest that they had ventured closer to the center and had been slung away, most likely by the twin black holes.

    Archival Hubble images, taken by the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), support the idea of twin black holes pushing stars away.

    NASA/Hubble NICMOS
    NASA/Hubble NICMOS

    The NICMOS images revealed that the galaxy’s core was unusually faint, indicating a lack of stars close to the galactic center. A star-depleted core distinguishes massive galaxies from standard elliptical galaxies, which are much brighter in their centers. Ma and her colleagues estimated that the amount of stars tossed out of the central region equals 40 billion suns, comparable to ejecting the entire disk of our Milky Way galaxy.

    See the full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 1:02 pm on March 23, 2016 Permalink | Reply
    Tags: , , , Black Holes   

    From AAS NOVA: ” Dance of Two Monster Black Holes” 

    AASNOVA

    Amercan Astronomical Society

    23 March 2016
    Susanna Kohler

    Binary black hole system in quasar OJ 287. Credit Gary Poyner
    Binary black hole system in quasar OJ 287. Credit Gary Poyner

    This past December, researchers all over the world watched an outburst from the enormous black hole in OJ 287 — an outburst that had been predicted years ago using the general theory of relativity.

    OJ 287 is one of the largest supermassive black holes known, weighing in at 18 billion solar masses. Located about 3.5 billion light-years away, this monster quasar is bright enough that it was first observed as early as the 1890s. What makes OJ 287 especially interesting, however, is that its light curve exhibits prominent outbursts roughly every 12 years.

    What causes the outbursts? Astronomers think that there is a second supermassive black hole, ~100 times smaller, inspiraling as it orbits the central monster and set to merge within the next 10,000 years. In this model, the primary black hole of OJ 287 is surrounded by a hot accretion disk. As the secondary black hole orbits the primary, it regularly punches through this accretion disk, heating the material and causing the release of expanding bubbles of hot gas pulled from the disk. This gas then radiates thermally, causing the outbursts we see.

    Attempts to model this scenario using Newtonian orbits all fail; the timing of the secondary black hole’s crossings through the accretion disk (as measured by when we see the outbursts) can only be explained by a model incorporating general-relativistic effects on the orbit. Careful observations and precise timing of these outbursts therefore provide an excellent test of general relativity.

    Watching a Predicted Crossing

    The model of OJ 287 predicted another disk crossing in December 2015, so professional and amateur astronomers around the world readied more than two dozen ground-based optical telescopes and the Swift/XRT satellite to observe OJ 287 in this time frame.

    NASA/SWIFT Telescope
    NASA/SWIFT

    The outburst occurred right on schedule, peaking on 5 December 2015, and the results of the observing campaign are now presented in a study led by Mauri Valtonen (University of Turku).

    Because the secondary black hole’s orbit is affected by the spin of the primary black hole, Valtonen and collaborators were able to use the timing of the outburst to measure the spin of OJ 287’s primary black hole to remarkably high precision. They find that its Kerr parameter is 0.313 ± 0.01 — which means it’s spinning at about a third of the maximum rate allowed by general relativity.

    The outburst timing also confirmed several general relativistic properties of the system, including its loss of energy to gravitational waves. Remarkably, the energy lost as the secondary black hole punches through the accretion disk is still ten thousand times smaller than the amount of energy it loses through gravitational waves!

    The observations from this outburst have provided important black-hole measurements and tests of general relativity — which are especially relevant in this new era of gravitational wave detections. And we may be able to perform still more tests on the secondary’s next pass through the disk, which should occur in 2019.

    Bonus

    Check out this awesome animation of the orbits in a system similar to OJ 287! The secondary’s orbit precesses around the primary due to general relativistic effects. The sound with the video is an audio representation of the increasing frequency as the two black holes inspiral. You can find more information about this animation here. [Steve Drasco & Curt Cutler]

    Access mp4 video here .

    Science team:

    M. J. Valtonen1,2, S. Zola3,4, S. Ciprini5,6, A. Gopakumar7, K. Matsumoto8, K. Sadakane8,
    M. Kidger9, K. Gazeas10, K. Nilsson1, A. Berdyugin2, V. Piirola1,2, H. Jermak11,
    K. S. Baliyan12, F. Alicavus13, D. Boyd14, M. Campas Torrent15, F. Campos16, J. Carrillo
    G´omez17, D. B. Caton18, V. Chavushyan19, J. Dalessio20, B. Debski3, D. Dimitrov21,
    M. Drozdz4, H. Er22, A. Erdem13, A. Escartin P´erez23, V. Fallah Ramazani2,
    A. V. Filippenko24, S. Ganesh12, F. Garcia25, F. G´omez Pinilla26, M. Gopinathan27,
    J. B. Haislip28, R. Hudec29, G. Hurst30, K. M. Ivarsen28, M. Jelinek29, A. Joshi27,
    M. Kagitani31, N. Kaur12, W. C. Keel32, A. P. LaCluyze28, B. C. Lee33, E. Lindfors2,
    J. Lozano de Haro34, J. P. Moore28, M. Mugrauer35, R. Naves Nogues15, A. W. Neely36,
    R. H. Nelson37, W. Ogloza4, S. Okano31, J. C. Pandey27, M. Perri5,38, P. Pihajoki39,
    G. Poyner40, J. Provencal20, T. Pursimo41, A. Raj33, D. E. Reichart28, R. Reinthal2,
    S. Sadegi2, T. Sakanoi31, J.-L. Salto Gonz´alez42, Sameer12, T. Schweyer43, M. Siwak4,
    F. C. Sold´an Alfaro44, E. Sonbas45, I. Steele11, J. T. Stocke46, J. Strobl29, L. O. Takalo2,
    T. Tomov47, L. Tremosa Espasa48, J. R. Valdes19, J. Valero P´erez49, F. Verrecchia5,38,
    J. R. Webb50, M. Yoneda51, M. Zejmo52, W. Zheng24, J. Telting41, J. Saario41,
    T. Reynolds41, A. Kvammen41, E. Gafton41, R. Karjalainen53, J. Harmanen2 and P. Blay54

    Institutions
    1Finnish Centre for Astronomy with ESO, University of
    Turku, Finland
    2Tuorla Observatory, Department of Physics and Astronomy,
    University of Turku, Finland
    3Astronomical Observatory, Jagiellonian University, ul.
    Orla 171, Cracow PL-30-244, Poland
    4Mt. Suhora Astronomical Observatory, Pedagogical
    University, ul. Podchorazych 2, PL30-084 Cracow, Poland
    5Agenzia Spaziale Italiana (ASI) Science Data Center,
    I-00133 Roma, Italy
    6Istituto Nazionale di Fisica Nucleare, Sezione di Perugia,
    I-06123 Perugia, Italy
    7Department of Astronomy and Astrophysics, Tata Institute
    of Fundamental Research, Mumbai 400005, India
    8Astronomical Institute, Osaka Kyoiku University, 4-
    698 Asahigaoka, Kashiwara, Osaka 582-8582, Japan
    9Herschel Science Centre, ESAC, European Space
    Agency, 28691 Villanueva de la Ca˜nada, Madrid, Spain
    10Department of Astrophysics, Astronomy and Mechanics,
    National & Kapodistrian University of Athens, Zografos
    GR-15784, Athens, Greece
    11Astrophysics Research Institute, Liverpool John
    Moores University, IC2, Liverpool Science Park, Brownlow
    Hill, L3 5RF, UK
    12Physical Research Laboratory, Ahmedabad 380009, India
    13Department of Physics, Faculty of Arts and Sciences,
    Canakkale Onsekiz Mart University, TR-17100 Canakkale,
    Turkey; Astrophysics Research Center and Ulupinar Observatory,
    Canakkale Onsekiz Mart University, TR-17100,
    Canakkale, Turkey
    145, Silver Lane, West Challow, Wantage, Oxon, OX12
    9TX, UK
    15C/ Jaume Balmes No 24 08348 Cabrils, Barcelona,
    Spain
    16C/.Riera, 1, 1o 3a Barcelona, Spain
    17Carretera deMartos 28 primero Fuensanta, Jaen, Spain
    18Dark Sky Observatory, Dept. of Physics and Astronomy,
    Appalachian State University, Boone, NC 28608, USA
    19Instituto Nacional de Astrofisica, ´Optica y Electr´onica,
    Apartado Postal 51-216, 72000 Puebla, M´exico
    20University of Delaware, Department of Physics and Astronomy,
    Newark, DE, 19716, USA
    21Institute of Astronomy and NAO, Bulg. Acad. Sc., 72
    Tsarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
    22Department of Astronomy and Astrophysics, Ataturk
    University, Erzurum, 25240, Turkey
    23Aritz Bidea No 8 4B (48100) Mungia Bizkaia, Spain
    24Department of Astronomy, University of California,
    Berkeley, CA 94720-3411, USA
    25Mu˜nas de Arriba La Vara, Vald´es (MPC J38) 33780
    Vald´es, Asturias – Spain
    26C/ Concejo de Teverga 9, 1C 28053 Madrid, Spain
    27Aryabhatta Research Institute of Observational Sciences
    (ARIES), Nainital, 263002 India
    28University of North Carolina at Chapel Hill, Chapel
    Hill, North Carolina NC 27599, USA
    29Astronomical Institute, The Czech Academy of Sciences,
    25165 Ondˇrejov, Czech Republic; Czech Technical
    University in Prague, Faculty of Electrical Engineering,
    Prague, Czech Republic
    3016 Westminster Close Basingstoke Hampshire RG22
    4PP, UK
    31Planetary Plasma and Atmospheric Research Center,
    Tohoku University, Sendai, Japan
    32Department of Physics and Astronomy and SARA Observatory,
    University of Alabama, Box 870324, Tuscaloosa,
    AL 35487, USA
    33Korea Astronomy and Space Science Institute, 776,
    Daedeokdae-Ro, Youseong-Gu, 305-348 Daejeon, KoreaRo Yuseong-Gu, 305-333 Daejeon,Korea
    34Partida de Maitino, pol. 2 num. 163 (03206) Elche,
    Alicante, Spain
    35Astrophysikalisches Institut und Universit¨ats-
    Sternwarte, Schillerg¨aßchen 2-3, D-07745 Jena, Germany
    36NF/Observatory, Silver City, NM 88041, USA
    371393 Garvin Street, Prince George, BC V2M 3Z1,
    Canada
    38INAF–Osservatorio Astronomico di Roma, via Frascati
    33, I-00040 Monteporzio Catone, Italy
    39Department of Physics, University of Helsinki, P.O.
    Box 64, FI-00014 Helsinki, Finland
    40BAA Variable Star Section, 67 Ellerton Road, Kingstanding,
    Birmingham B44 0QE, UK
    41Nordic Optical Telescope, Apartado 474, E-38700
    Santa Cruz de La Palma, Spain
    42Observatori Cal Maciarol m`odul 8. Masia Cal Maciarol,
    cam´ı de l’Observatori s/n 25691 `Ager, Spain
    43Max Planck Institute for Extraterrestrial Physics,
    Giessenbachstrasse, D-85748 Garching, Germany; Technische
    Universit¨at M¨unchen, Physik Department, James-
    Franck-Str., D-85748 Garching, Germany
    44C/Petrarca 6 1a 41006 Sevilla, Spain
    45University of Adiyaman, Department of Physics, 02040
    Adiyaman, Turkey
    46Center for Astrophysics and Space Astronomy, Department
    of Astrophysical and Planetary Sciences, Box 389,
    University of Colorado, Boulder, CO 80309, USA
    47Centre for Astronomy, Faculty of Physics, Astronomy
    and Informatics, Nicolaus Copernicus University, ul.
    Grudziadzka 5, 87-100 Torun, Poland
    48C/Cardenal Vidal i Barraquee No 3 43850 Cambrils,
    Tarragona, Spain
    49C/Matarrasa, 16 24411 Ponferrada, Le´on, Spain
    50Florida International University and SARA Observatory,
    University Park Campus, Miami, FL 33199, USA
    51Kiepenheuer-Institut fur Sonnenphysic, D-79104,
    Freiburg, Germany
    52Janusz Gil Institute of Astronomy, University of
    Zielona G´ora, Szafrana 2, PL-65-516 Zielona G´ora, Poland
    53Isaac Newton Group of Telescopes, Apartado 321, E-
    38700 Santa Cruz de La Palma, Spain
    54IAC-NOT, C/Via Lactea, S/N, E38205, La Laguna,
    Spain
    and Korea University of Science and Technology, Gajeong-

    Observatories:
    Tuorla Observatory in
    Finland,

    4
    Tuorla Observatory

    Mount Suhora Observatory of the Pedagogical
    University and Astronomical Observatory
    of the Jagiellonian University in Poland,

    4
    Mount Suhora Observatory

    University of Athens in Greece,

    Mount Abu Infrared Observatory in India,
    5
    Mount Abu Infrared Observatory in India

    Liverpool Telescope,

    Liverpool Telescope
    Liverpool Telescope

    Kungliga Vetenskapliga Akademien Telescope,

    Nordic Optical Telescope
    Nordic Optical telescope (NOT),
    Nordic Optical telescope

    William Herschel Telescope using ACAM instrument, in La
    Palma, Canary Islands, Spain (see Pihajoki et al.
    (2013) for details).

    ING William Herschel Telescope
    ING William Herschel Telescope

    Other telescopes participating
    were

    0.41 m CTIO/PROMPT5 telescope in Chile
    (Reichart et al. 2005),
    6
    CTIO/PROMPT5 telescope

    the 0.6 m SARA telescope
    at the Cerro Tololo InterAmerican Observatory,
    7
    SARA telescope

    the 0.51 m reflector in Osaka Kyoiku University,
    Japan,

    the 0.25 m Cassegrain and 0.9/0.6 m
    Schmidt telescopes of the University ObservatoryJena, Germany (Mugrauer & Berthold 2010;Mugrauer 2016),
    8
    University Observatory Jena

    the 0.77 m Schmidt Camera ofTonantzintla in Mexico,
    9
    The 77 cm Schmidt-telescope from 1966 at Brorfelde Observatory

    the 0.60 m and 1.22 m reflectors
    of the Canakkale Onsekiz Mart University
    Observatory,

    the 0.60 m telescope of the Universityof Adiyaman

    and the 0.60 m telescope at the
    TUBITAK National Observatory, Turkey
    10
    TÜBİTAK National Observatory at Bakırtepe, Antalya Province, Turkey

    and the
    0.50 m robotic telescope at the Ondrejov Observatory,
    Czech Republic.

    In the continental US the
    photometric data were gathered with the 0.9 m
    SARA telescope at Kitt Peak (above)

    the 0.40 m telescope
    of Florida International University,

    the 0.76 m
    Katzman Automatic Imaging Telescope (KAIT)
    at the Lick Observatory, UC Santa Cruz (Filippenko et al. 2001),
    UC Berkeley KAIT telescope
    UC Berkeley KAIT telescope at Lick Observatory, UC Santa Cruz

    the 0.40 m University of Alabama campus telescope
    11
    .40 meter Ritchey telescope

    and the 0.40 m Arizona State University
    campus telescope.

    OJ 287 was measured through
    the wide band R filter in most sites. Only the
    KAIT data were taken without any filter and
    transformed into the R band. We performed differential
    photometry on images calibrated for bias,
    dark and flatfield with the aperture method. We
    used GSC 1400-222 (R = 13.74 mag) as the comparison
    star and GSC 1400-444 as the check star.
    Measurements with the DIPOL-2 polarimeter
    (Piirola et al. 2014) installed on the remotely
    controlled, 0.60 m telescope at the Haleakala observatory
    (Tohoku University) were carried out on
    13 nights in the interval 2015 Nov 30 – Dec 15 (UT

    See the full article here .

    Please help promote STEM in your local schools.

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  • richardmitnick 12:56 pm on March 18, 2016 Permalink | Reply
    Tags: , , Black Holes, ,   

    From Ethan Siegel: “Could the Large Hadron Collider make an Earth-killing black hole?” 

    Starts with a bang
    Starts with a Bang

    3.18.16
    Ethan Siegel

    No. Not even if you violate the laws of physics in two fundamental ways.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    John Oliver: So, roughly speaking, what are the chances that the world is going to be destroyed? One-in-a-million? One-in-a-billion?
    Walter Wagner: Well, the best we can say right now is a one-in-two chance.
    John: 50–50?
    Walter: Yeah, 50–50… It’s a chance, it’s a 50–50 chance.
    John: You come back to this 50–50 thing, what is it Walter?
    Walter: Well, if you have something that can happen and something that won’t necessarily happen, it’s going to either happen or it’s gonna not happen. And, so, it’s kind of… best guess at this point.
    John: I’m… not sure that’s how probability works, Walter. –The Daily Show

    Every time we push the frontiers of knowledge, it comes with a risk, and it comes with the prospect of a reward. The risks are many: failure to find anything new, futility of the experiment to function as designed, and even the possibility of damage and destruction if things go awry. But the rewards can be tremendous, including the unlocking of new knowledge, the development of new technologies, and the advancement of the entire human enterprise of science.

    One of the places that personifies all of this is the Large Hadron Collider (LHC) at CERN, where we’ve begun colliding protons at the highest energies ever achieved in a particle accelerator. A few years ago, we broke the old record — 2 TeV (tera-electron-Volts, or 10¹² eV), which was set at Fermilab — by accelerating each particle up to 3.5 TeV and smashing them into one another, achieving 7 TeV of total energy. This discovery enabled us to not only create huge numbers of a great many elusive, fundamental particles (like the top quark [found at FNAL by the Tevatron], as well as the W-and-Z bosons), but enabled us to discover a brand new fundamental particle and last undiscovered particle in the standard model: the Higgs boson.

    CERN ATLAS Higgs Event
    Higgs event at LHC/ATLAS
    CERN ATLAS New
    ATLAS

    Higgs Boson Event
    Higgs Event at CERN/CMS
    CERN CMS New
    CMS

    FNAL Tevatron
    FNAL CDF
    FNAL DZero
    Tevatron at FNAL, and its two experiments, CDF and D0

    Standard model with Higgs New
    Standard Model of Particle Physics

    Upgrades to the LHC now enable us to reach somewhere between (depending on whom you ask) 13-and-14 TeV of total energy. If we’re really lucky, the sheer number of collisions at these tremendous energies, combined with the incredible detectors we have in place, may allow us to create and discover never-before-seen particles in this laboratory. Of course, that hasn’t stopped the usual suspects from making incredible (and completely non-credible) claims, such as:

    Scientists at Large Hadron Collider hope to make contact with PARALLEL UNIVERSE in days,
    Big Bang theory could be debunked by Large Hadron Collider, and
    That poking at the Universe may wind up destroying it by creating a black hole that swallows us.

    While the first two are just bad science reporting, the third one is a common fear that’s reared its ugly head time and time again, and has no basis in reality.

    So what’s the big idea, and how do we know it’s wrong? Let’s find out.

    There are a number of theories that predict the existence of extra dimensions. Not merely the three spatial and one time dimension we know to be present in our four-dimensional spacetime, but at least one additional spatial dimension that exists in our Universe. While we can’t quite access those dimensions at the energies we’ve probed, it’s conceivable that at scales that are smaller than those we’ve examined — which corresponds to higher energies — these extra dimensions exist.

    And if these extra dimensions exist, one theoretical possibility is that it might be possible to create tiny, miniature, microscopic black holes!

    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital
    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital

    If we could do this, this would be an incredible feat of technology, of science, and an amazing piece of evidence that would change our understanding of the Universe forever. Of course, however, you say the words “black holes” and people immediately get this catastrophic picture of something sucking in all sorts of matter, progressively eating the protons, neutrons and electrons that make up our world, and eventually destroying the entire thing.

    This is not possible. In fact, there are three reasons we know this is not possible. Let’s go over them one at a time.

    1.) If these miniature black holes exist, the Earth has been getting hit by them for billions of years, and it’s still here.

    Sure, we’ve never created particles of this energy in a laboratory setting before. But at the very highest of energies — energies more than a hundred million (100,000,000) times greater than what we create at the LHC — particles smack into Earth constantly: the great cosmic rays that bombard us from all directions in space.

    These black holes, if they exist, would have been bombarding Earth (and all the planets) for the entire history of our Solar System, as well as the Sun, and there is absolutely no evidence that any body in our Solar System ever became a black hole or got eaten by one.

    But maybe, you’ll object, these objects were moving too quickly, and so they’ll simply pass through the Earth, eating too little matter to remain inside, and pass through to intergalactic space. Well, if that’s your objection, perhaps this second reason-why-this-is-impossible will help you out.

    2.) If you do create a miniature black hole, they will decay, via Hawking Radiation, on ridiculously small timescales.

    If there are extra dimensions, it is conceivable that they could be of a specific type allowing the (again, very rare, but plausible) formation of a microscopic black hole. This black hole will have, at most, a mass equal to the energy of the proton-proton collision, or up to 13-to-14 TeV. That corresponds, via E=mc^2, to a mass of just 5 x 10^-20 grams, and most likely less.

    But, even if you have extra dimensions of the right scale, and of the right type,and you make this black hole, you still have a problem: it’s unstable. Due to the laws of quantum mechanics, this black hole is going to decay by a process known as Hawking radiation. For a black hole of mass 5 x 10^-20 grams, the decay time in three dimensions would be about 10^-83 seconds, which is not even enough time to exist! For physics to be meaningful, we need a time of about 10^-43 seconds or longer. Translated into black hole mass, we’d need it to be at least 0.00002 grams to have even a chance of existing.

    3.) You can compute the rate at which a black hole eats matter, and it’s not even close to being as small as the lifetime of our planet.

    We like to think of black holes as “sucking” in matter, but the truth of the matter is, they can only interact with it gravitationally. At a mass of ~5 x 10^-20 grams, that gravitational force it exerts is incredibly weak: all it can manage to do is pass into the Earth’s center and out again, hoping for a collision with an elementary particle as it does so. While the black hole’s cross-section is tiny, the cross-section of a proton (or neutron) is pretty large, and so we can assume — for the sake of argument — that every time the black hole strikes a proton or neutron, it absorbs it.

    Assuming it eats every proton, neutron, or electron that it comes in contact with — and also taking into account its gravity, to see what it attracts — it will eat about 66,000 protons and neutrons per second. Of course, 66,000 protons-and-neutrons is a tiny amount in terms of mass: 1.1 x 10^-25 grams. That rate-of-growth will be constant until the black hole becomes quite large; only at about one billion metric tonnes will the black hole will start to grow faster than this rate, as it takes that long for its cross-section to increase. Capturing 66,000 nucleons per second, how long will it take to get the black hole up to even one kilogram? Three trillion years, which is much longer than the lifetime of the Sun or even the age of the Universe.

    Inflationary Universe. NASA/WMAP
    NASA/WMAP

    So even if you make a black hole, and even if the laws of physics that we know are wrong and it lives forever, it is still harmless. No matter how many of the laws of physics you throw out, revise or tweak, the Earth will still be okay.

    So take heart! We’re all set to probe the frontiers of physics, to increase our knowledge and understanding of the Universe, and to do it in a totally safe way. Any fears you may have concerning our planet getting eaten by a black hole are completely irrational, and now — armed with the scientific knowledge of why — you can rest easy. The world is safe. At least, from physics.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “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 8:03 pm on March 16, 2016 Permalink | Reply
    Tags: , , Black Holes, ,   

    From NOVA: “Are Black Holes Real?” This is a MUST READ 

    PBS NOVA

    NOVA

    10 Mar 2016
    Kate Becker

    Not so long ago, black holes were like unicorns: fantastical creatures that flourished on paper, not in life. Today, there is wide scientific consensus that black holes are real. Even though they can’t be observed directly—by definition, they give off no light—astronomers can infer their hidden presence by watching how stars, gas, and dust swirl and glow around them.

    But what if they’re wrong? Could something else—massive, dense, all-but-invisible—be concealed in the darkness?

    While black holes have gone mainstream, a handful of researchers are investigating exotic ultra-compact stars that, they argue, would look exactly like black holes from afar. Well, almost exactly. Though their ideas have been around for many years, researchers are now putting them to the most stringent tests ever, looking to show once and for all that what looks and quacks like a black hole really is a black hole. And if not? Well, it could just spark the next revolution in physics.

    The game-changer is a new experiment called the Event Horizon Telescope (EHT).

    Event Horizon Telescope map
    EHT map

    The EHT is a network of telescopes that are sensitive to radio waves about a millimeter long and linked together using a technique called very long baseline interferometry. Baseline refers to the distance between the networked telescopes: the longer the distance, the finer the details the telescope can pick out. It’s impossible—or at least impractical—to build a single telescope as big as planet Earth, but astronomers can achieve the same “zoom” factor by linking telescopes on opposite continents. Just like that, the universe goes from standard-definition to HD: a switch powerful enough to tell a black hole from an exotic imposter.

    Meanwhile, scientists have directly detected gravitational waves for the first time using the Laser Interferometer Gravitational-Wave Observatory, also known as LIGO.

    MIT Caltech  Advanced aLIGO Hanford Washington USA installation
    MIT Caltech Advanced aLIGO, Hanford, Washington, USA installation

    Gravitational waves—ripples in the fabric of space-time that [Albert] Einstein predicted should radiate out from the site of any gravitational disturbance—represent an entirely new way to see the cosmos, and with enough data, they could finally confirm—or contradict—the existence of black holes.

    Black Hole Anatomy

    On its own, a black hole looks like nothing: black-on-black, indistinguishable from the empty space that surrounds it. But supermassive black holes, which are believed to sit at the core of almost every galaxy in the universe, surrounded by stars and other galactic detritus that accumulates around the edge like soap suds circling the bathtub drain. By studying those “suds,” astronomers can answer questions about the central black hole.

    The best-studied black hole candidate in the universe is the one called Sagittarius A* [Sag A*], which lives at the center of our very own Milky Way galaxy.

    Sag A prime
    Sag A*

    By tracking the orbits of stars circling around Sagittarius A*, they have deduced that Sagittarius A* packs some 4 million times the mass of the Sun into a region of space much smaller than the solar system. Their conclusion: it could only be a supermassive black hole.

    To confirm that suspicion, they would like to see up to the edge of the black hole—the event horizon, a sort of line in the sand that separates the “inside” of the black hole from the “outside” and beyond which nothing can escape. From the perspective of a telescope on Earth, the event horizon should look like a dark shadow surrounded by a bright ring of light. The exact shape of this ring and shadow are predicted by the equations of general relativity, plus the properties of the black hole and its surroundings.

    An Earth-Sized Telescope

    That’s where the EHT comes in. Since the EHT first started taking data, it has been building its telescope roster, and with each new member, it gets closer to making the first true image of a black hole shadow.

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

    Atacama Pathfinder EXperiment (APEX)

    ESO APEX

    Atacama Submillimeter Telescope Experiment (ASTE)

    Atacama Submillimeter Telescope Experiment (ASTE) (ASTE)

    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    CARMA Array

    Caltech Submillimeter Observatory (CSO)

    Caltech Submillimeter Observatory

    Institut de Radioastronomie Millimetrique (IRAM) 30m

    IRAM 30m Radio telescope

    James Clerk Maxwell Telescope (JCMT)

    East Asia Observatory James Clerk Maxwell telescope

    The Large Millimeter Telescope (LMT) Alfonso Serrano

    Large Millimeter Telescope Alfonso Serrano

    The Submillimeter Array (SMA)

    CfA Submillimeter Array Hawaii SAO

    Future Array/Telescopes

    Atacama Large Millimeter/submillimeter Array (ALMA)

    ALMA Array

    Plateau de Bure interferometer

    Plateau de Bure interferometer

    The EHT is like an all-star team of telescopes: Most days, its millimeter-wave dishes run their own experiments independently, but for one or two weeks a year, they team up to become the EHT, taking new data and running tests during the brief window when astronomers can expect clear weather at sites from Hawaii to Europe to the South Pole.

    “It sounds too good to be true that you just drop telescopes around the world and ‘poof!’ you have an Earth-sized telescope,” says Avery Broderick, a theoretical astrophysicist at University of Waterloo and the Perimeter Institute. And in a way, it is. The EHT doesn’t make pictures. Instead, it turns out a kind of mathematical cipher called a Fourier transform, which is like the graphic equalizer on your stereo: it divvies up the incoming signal, whether its an image of space or a piece of music, into the different frequencies that make it up and tells you how much power is stored in each frequency. So far, the EHT has only given astronomers a look at a few scattered pixels of the Fourier transform. When they compare those pixels to what they expect to see in the case of a true black hole, they find a good match. But the job is like trying to figure out whether you’re listening to Beethoven or the Beastie Boys based only on a few slivers of the graphic equalizer curve.

    Now, the EHT is about to add a superstar player: the [ESO/NRAO/NAOJ]Atacama Large Millimeter Array, a telescope made up of 66 high-precision dishes sited 16,000 feet above sea level in Chile’s clear, dry Atacama desert. With ALMA on board, the EHT will finally be able to make the leap from fitting models to seeing a complete picture of the black hole’s shadow. EHT astronomers are now rounding up time at all of the telescopes so that they can take new data and assemble that first coveted image in 2017.

    And if they don’t see what they expect? It could mean that the black hole isn’t really a black hole at all.

    That would come as a relief to many theorists. Black holes are mothers of cosmic paradox, keeping physicists up at night with the puzzles they present: Do black holes really destroy information? Do they really contain infinitely dense points called singularities? Black holes are also the battlefield on which general relativity and quantum mechanics clash most dramatically. If it turns out that they don’t actually exist, some physicists might sleep a little better.

    But if they’re not black holes, then what could they be? One possibility is that they are dark stars made up of bosons, subatomic particles that, unlike more familiar electrons and protons, obey strange rules that allow more than one of them to be in the same place at the same time. Boson stars are highly speculative—astronomers have never seen one, as far as they know—but theorists like Vitor Cardoso, a professor of physics at Técnico in Lisbon and a distinguished visiting researcher at Sapienza University of Rome, hypothesize that some or all of the objects we think are supermassive black holes could actually be boson stars in disguise.

    Physicists classify particles into two different categories: fermions, which include protons, electrons, neutrons, and their components; and bosons, like photons (light particles), gluons, and Higgs particles. Every star that we’ve ever seen shining is dominated by fermions. But, Cardoso says, given a starting environment rich in bosons, bosons could “clump” together gravitationally to form stars, just as fermions do. The early universe might have had a high enough density of bosons for boson stars to form.

    But not every boson is a suitable building block for a boson star. Gravity won’t hold together a clump of massless photons, for instance. Higgs particles are massive enough to be bound together by gravity, but they aren’t stable—they only exist for tiny fraction of a second before decaying away. Theorists have speculated about ways to stabilize Higgs particles, but Cardoso is more intrigued by the prospect that other, yet-undiscovered heavy bosons, like axions, could make up boson stars. In fact, some physicists hypothesize that massive bosons like these could be responsible for dark matter—meaning that boson stars wouldn’t just be a solution to the riddle of black holes, they could also tell us what, exactly, dark matter is.

    Gravastars

    Boson stars aren’t the only black hole doppelgänger that theorists have dreamed up. In 2001, researchers proposed an even more speculative oddity called a gravastar. In the gravastar model, as a would-be black hole collapses under its own weight, extreme gravity combines with quantum fluctuations that are constantly jiggling through space to create a bubble of exotic spacetime that halts the cave-in.

    Theorists don’t really know what’s inside that bubble, which is both good and bad news for gravastars: Good news because it gives theorists the flexibility to revise the model as new observations come in, bad news because scientists are rightly skeptical of any model that can be patched up to match the data.

    When the data does come in, physicists have a checklist of sorts that should help them know which of the three—black hole, boson star, or gravastar—they’re looking at. A gravastar should have a bright surface that’s distinguishable from the glowing ring predicted to loop around a black hole. Meanwhile, if the object at the center of the Milky Way is actually a boson star, Cardoso predicts, it will look more like a “normal” star. “Black holes are black all the way through,” Cardoso says. “If really the object is a boson star, then the luminous material can in principle pile up at its center. A bright spot should be detected right at the center of the object.”

    A New View

    Most physicists have placed their bets on Saggitarius A* and other candidates being black holes, though. Boson stars and gravastars already have a few strikes against them. First, when it comes to scientific credibility, black holes have a major head start. Astronomers have a solid understanding of the process by which black holes form and have direct evidence that other ultra-dense objects, like white dwarfs and neutron stars, which could merge to form black holes, really do exist. The alternatives are more speculative on every count.

    Furthermore, Broderick says, astronomers have looked for the telltale signature of boson stars and gravastars at the center of the Milky Way—and haven’t found it. “The stuff raining down on the object will give up all its kinetic energy—all the gravitational binding energy tied up in the kinetic energy of its fall—resulting in a thermal bump in the spectrum,” Broderick says —that is, a signature spike in infrared emission. In 2009, astrophysicists reported that they had found no such bump coming from Sagittarius A*, and in 2015, they announced that it was missing from the nearby massive galaxy [Messier]87, too.

    Cardoso doesn’t see this as a death-knell for the boson star model, though. “The field that makes up the boson star hardly interacts with matter,” he says. To ordinary matter, the surface of a boson star would feel like frothed milk. “We do not yet have a complete model of how these objects accrete luminous matter,” Cardoso says, “so I think that it’s fair to say that this is still an open question.” He is less optimistic about gravastars, which he describes as “artificial constructs” that are likely ruled out by the latest observations.

    As the LIGO experiment gathers more data, theorists will get more opportunities to test their exotic hypotheses with gravitational waves. As two massive objects—say, a supermassive black hole and a star—spiral toward each other on the way toward a collision, gravitational waves carry away the energy of their motion. If one member of the spiraling pair is a black hole, the gravitational wave signal will cut off abruptly as the star passes through the black hole’s event horizon. “It gives rise to a very characteristic ringdown in the final stages of the inspiral,” Cardoso says. Because the alternative models have no such horizon, the gravitational wave signal would keep on reverberating.

    Most astronomers believe that the waves LIGO detected were given off by the collision of two black holes, but Cardoso thinks that boson stars shouldn’t be ruled out just yet. “The data is, in principle, compatible with the two colliding objects being each a boson star,” he says. The end result, though, is probably a black hole “because it rings down very fast.”

    LIGO is not designed to pick up signals at the frequency at which supermassive objects like Sagittarius A* are expected to “ring.” (LIGO is tuned to recognize gravitational waves from smaller black holes and dense stars like neutron stars.) But supermassive black holes and boson stars are in the sweet spot for the planned space-based gravitational wave telescope ESA/LISA (the Evolved Laser Interferometer Space Antenna), slated for launch in 2034.

    ESA LISA Pathfinder
    ESA/LISA

    “To confirm or rule out boson stars entirely, we need ‘louder’ observations,” Cardoso says. “EHT or eLISA are probably our best bet.”

    Taking the Pulse

    In the meantime, astronomers could measure waves from these extremely massive objects by precisely clocking the arrival times of radio pulses from a special class of dead stars called pulsars. If astronomers spot pulses arriving systematically off-beat, that could be a sign that the space they’ve been traveling across is being stretched and squeezed by gravitational waves. Three collaborations—NANOGrav in North America, the European Pulsar Timing Array, and the Parkes Pulsar Timing Array in Australia—are already scanning for these signals using radio telescopes scattered around the globe.

    To Broderick, though, the big question isn’t which model will win out, it’s whether these new experiments can find a flaw in general relativity. “For 100 years, general relativity has been enormously successful, and there’s no hint of where it breaks,” he says. Yet general relativity and quantum mechanics, which appears equally shatterproof, are fundamentally incompatible. Somewhere, one or both must break down. But where? Boson stars and gravastars might not be the answer. Still, exploring these exotic possibilities forces physicists to ask the questions that might lead them to something even more profound.

    “We expect that general relativity will pass the EHT’s tests with flying colors,” Broderick says. “But the great hope is that it won’t, that we’ll finally find the loose thread to pull on that will unravel the next great revolution in physics.”

    See the full article here .

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

     
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