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  • richardmitnick 12:56 pm on October 15, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , , , ,   

    From The Guardian: “Black holes and soft hair: why Stephen Hawking’s final work is important” 

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    From The Guardian

    Malcolm Perry, who worked with Hawking on his final paper, explains how it improves our understanding of one of universe’s enduring mysteries.

    10 Oct 2018
    Ian Sample

    Black Hole Entropy and Soft Hair was completed in the days before the physicist’s death in March.

    1
    An artist’s impression of a star being torn apart by a black hole. Photograph: NASA’s Goddard Space Flight Center.

    Stephen Hawking by Jason Bye/REX/Shutterstock

    The information paradox is perhaps the most puzzling problem in fundamental theoretical physics today. It was discovered by Stephen Hawking 43 years ago, and until recently has puzzled many.

    Starting in 2015, Stephen, Andrew Strominger and I started to wonder if we could understand a way out of this difficulty by questioning the basic assumptions that underlie the difficulties. We published our first paper on the subject in 2016 and have been working hard on this problem ever since.

    The most recent work, and perhaps the last paper that Stephen was involved in, has just come out. While we have not solved the information paradox, we hope that we have paved the way, and we are continuing our intensive work in this area.

    Physics is really about being able to predict the future given how things are now. For example, if you throw a ball, once you know its initial position and velocity, then you can figure out where it will be in the future. That kind of reasoning is fine for what we call classical physics but for small things, like atoms and electrons, the rules need some modifications, as described by quantum mechanics. In quantum mechanics, instead of describing precise outcomes, one finds that one can only calculate the probabilities for various things to happen. In the case of a ball being thrown, one would not know its precise trajectory, but only the probability that it would be in some particular place given its initial conditions.

    What Hawking discovered was that in black hole physics, there seemed to be even greater uncertainty than in quantum mechanics. However, this kind of uncertainty seemed to be completely unacceptable in that it resulted in many of the laws of physics appearing to break down. It would deprive us of the ability to predict anything about the future of a black hole.

    That might not have mattered – except that black holes are real physical objects. There are huge black holes at the centres of many galaxies. We know this because observations of the centre of our galaxy show that there is a compact object with a mass of a few million times that of our sun there; such a huge concentration of mass could only be a black hole. Quasars, extremely luminous objects at the centres of very distant galaxies, are powered by matter falling onto black holes. The observatory Ligo has recently discovered ripples in spacetime, gravitational waves, produced by the collision of black holes.

    The root of the problem is that it was once thought that black holes were completely described by their mass and their spin. If you threw something into a black hole, once it was inside you would be unable to tell what it was that was thrown in.

    These ideas were encapsulated in the phrase “a black hole has no hair”. We can often tell people apart by looking their hair, but black holes seemed to be completely bald. Back in 1974, Stephen discovered that black holes, rather than being perfect absorbers, behave more like what we call “black bodies”. A black body is characterised by a temperature, and all bodies with a temperature produce thermal radiation.

    If you go to a doctor, it is quite likely your temperature will be measured by having a device pointed at you. This is an infrared sensor and it measures your temperature by detecting the thermal radiation you produce. A piece of metal heated up in a fire will glow because it produces thermal radiation.

    Black holes are no different. They have a temperature and produce thermal radiation. The formula for this temperature, universally known as the Hawking temperature, is inscribed on the memorial to Stephen’s life in Westminster Abbey. Any object that has a temperature also has an entropy. The entropy is a measure of how many different ways an object could be made from its microscopic ingredients and still look the same. So, for a particular piece of red hot metal, it would be the number of ways the atoms that make it up could be arranged so as to look like the lump of metal you were observing. Stephen’s formula for the temperature of a black hole allowed him to find the entropy of a black hole.

    The problem then was: how did this entropy arise? Since all black holes appear to be the same, the origin of the entropy was at the centre of the information paradox.

    What we have done recently is to discover a gap in the mathematics that led to the idea that black holes are totally bald. In 2016, Stephen, Andy and I found that black holes have an infinite collection of what we call “soft hair”. This discovery allows us to question the idea that black holes lead to a breakdown in the laws of physics.

    Stephen kept working with us up to the end of his life, and we have now published a paper that describes our current thoughts on the matter. In this paper, we describe a way of calculating the entropy of black holes. The entropy is basically a quantitative measure of what one knows about a black hole apart from its mass or spin.
    While this is not a resolution of the information paradox, we believe it provides some considerable insight into it. Further work is needed but we feel greatly encouraged to continue our research in this area. The information paradox is intimately tied up with our quest to find a theory of gravity that is compatible with quantum mechanics.

    Einstein’s general theory of relativity is extremely successful at describing spacetime and gravitation on large scales, but to see how the world works on small scales requires quantum theory. There are spectacularly successful theories of the non-gravitational forces of nature as explained by the “standard model” of particle physics. Such theories have been exhaustively tested and the recent discovery of the Higgs particle at Cern by the Large Hadron Collider is a marvellous confirmation of these ideas.

    Yet the incorporation of gravitation into this picture is still something that eludes us. As well as his work on black holes, Stephen was pursuing ideas that he hoped would lead to a unification of gravitation with the other forces of nature in a way that would unite Einstein’s ideas with those of quantum theory. Our work on black holes does indeed shed light on this other puzzle. Sadly, Stephen is no longer with us to share our excitement about the possibility of resolving these issues, which have now been around for half a century.

    The origins of the puzzle can be traced back to Albert Einstein. In 1915, Einstein published his theory of general relativity, a tour-de-force that described how gravity arises from the spacetime-bending effects of matter, and so why the planets circle the sun. But Einstein’s theory made important predictions about black holes too, notably that a black hole can be completely defined by only three features: its mass, charge, and spin.

    Nearly 60 years later, Hawking added to the picture. He argued that black holes also have a temperature. And because hot objects lose heat into space, the ultimate fate of a black hole is to evaporate out of existence. But this throws up a problem. The rules of the quantum world demand that information is never lost. So what happens to all the information contained in an object – the nature of a moon’s atoms, for instance – when it tumbles into a black hole?

    “The difficulty is that if you throw something into a black hole it looks like it disappears,” said Perry. “How could the information in that object ever be recovered if the black hole then disappears itself?”

    In the latest paper, Hawking and his colleagues show how some information at least may be preserved. Toss an object into a black hole and the black hole’s temperature ought to change. So too will a property called entropy, a measure of an object’s internal disorder, which rises the hotter it gets.

    The physicists, including Sasha Haco at Cambridge and Andrew Strominger at Harvard, show that a black hole’s entropy may be recorded by photons that surround the black hole’s event horizon, the point at which light cannot escape the intense gravitational pull. They call this sheen of photons “soft hair”.

    “What this paper does is show that ‘soft hair’ can account for the entropy,” said Perry. “It’s telling you that soft hair really is doing the right stuff.”

    It is not the end of the information paradox though. “We don’t know that Hawking entropy accounts for everything you could possibly throw at a black hole, so this is really a step along the way,” said Perry. “We think it’s a pretty good step, but there is a lot more work to be done.”

    Days before Hawking died, Perry was at Harvard working on the paper with Strominger. He was not aware how ill Hawking was and called to give the physicist an update. It may have been the last scientific exchange Hawking had. “It was very difficult for Stephen to communicate and I was put on a loudspeaker to explain where we had got to. When I explained it, he simply produced an enormous smile. I told him we’d got somewhere. He knew the final result.”

    Among the unknowns that Perry and his colleagues must now explore are how information associated with entropy is physically stored in soft hair and how that information comes out of a black hole when it evaporates.

    “If I throw something in, is all of the information about what it is stored on the black hole’s horizon?” said Perry. “That is what is required to solve the information paradox. If it’s only half of it, or 99%, that is not enough, you have not solved the information paradox problem.

    “It’s a step on the way, but it is definitely not the entire answer. We have slightly fewer puzzles than we had before, but there are definitely some perplexing issues left.”

    Marika Taylor, professor of theoretical physics at Southampton University and a former student of Hawking’s, said: “Understanding the microscopic origin of this entropy – what are the underlying quantum states that the entropy counts? – has been one of the great challenges of the last 40 years.

    “This paper proposes a way to understand entropy for astrophysical black holes based on symmetries of the event horizon. The authors have to make several non-trivial assumptions so the next steps will be to show that these assumptions are valid.”

    Juan Maldacena, a theoretical physicist at Einstein’s alma mater, the Institute for Advanced Studies in Princeton, said: “Hawking found that black holes have a temperature. For ordinary objects we understand temperature as due to the motion of the microscopic constituents of the system. For example, the temperature of air is due to the motion of the molecules: the faster they move, the hotter it is.

    “For black holes, it is unclear what those constituents are, and whether they can be associated to the horizon of a black hole. In some physical systems that have special symmetries, the thermal properties can be calculated in terms of these symmetries. This paper shows that near the black hole horizon we have one of these special symmetries.”

    See the full article here .

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  • richardmitnick 8:15 am on September 5, 2018 Permalink | Reply
    Tags: A Type IV civilization would be undetectable to us, A Type V master race that would function like gods able to harness energy not only from this universe but all universes in all dimensions, , At 100000 times the energy usage we have now we’d have access to 10¹⁷ watts of energy as a Type I civilization, , Black Holes, , Dyson ring and Dyson bubble, , Micro-scale developed by John D. Barrow, , Physicist Michio Kaku, The Kardashev scale designed by astrophysicist Nikolai Kardashev, The trick for a galactic species would be the constraints of the laws of physics, These feats are very sci-fi and as far as we know impossible to accomplish. But then again we’re a lowly Type 0 civilization with no idea what may lie ahead, To colonize all the stars we could use self-replicating robots that would assemble and maintain the Dyson swarms, We’re a Type Zero Civilization   

    From Medium: “We’re a Type Zero Civilization” 

    From Medium

    Aug 11, 2018
    Updated 9.5.18
    Ella Alderson

    When will we move up the scale?

    1
    Image: Juanmrgt/iStock/Getty Images Plus

    The Kardashev scale, designed by astrophysicist Nikolai Kardashev, was created to assess how advanced a civilization is by taking into consideration multiple factors, including population growth, technology, and energy demands. The idea is that the more advanced the people are, the higher and more complex their energy usage will be. When we first appeared on Earth 200,000 years ago, for example, our species was few in number, and the extent of our energy source was, really, just fire. We now number in the billions and use a combination of wind, solar, and nuclear energy sources, though our main energy supply comes from fossil fuels (it really seems like we just moved on to burning bigger and badder things). The International Energy Agency estimates that each year our societies use an estimated 17.37 terrawatt-hours.

    All of this may sound fairly advanced — we’ve come a long way from just using logs to fuel our everyday lives. Yet in reality, we’re really quite primitive compared to where we could be. We still get the majority of our energy from dead plants and animals, a source that will eventually run out sooner or later, and which is helping destroy our planet in the process.

    So where do we place on the Kardashev scale? We’re a zero: 0.72, to be more exact. Here’s what we need to move forward.

    Type I

    To become a Type I civilization we would have to harness all the available energy of our home planet at 100% efficiency. This means capturing the energy of every wave, every beam of sunlight, and every bit of fossil fuel we can dig up. To do that without rendering the entire planet uninhabitable, we’d have to use nuclear fusion. And to create all the energy we need via this method, we would require 280 k/s of hydrogen and helium every second, or 89 billion grams of hydrogen per year. You can gather more than that from one square km of ocean water.

    With this ability to harness all energy from Earth also comes the ability to control all of the planet’s natural forces, including volcanoes, geothermal vents, earthquakes, and climate. At 100,000 times the energy usage we have now, we’d have access to 10¹⁷ watts of energy as a Type I civilization. Consider, for example, the ability to control a hurricane. One such storm can release the power of hundreds of hydrogen bombs.

    While controlling the weather may sound very fantastical, physicist Michio Kaku theorizes that we’ll reach Type I status in the next 100–200 years, as we continue to grow in population at about 3% per year.

    2
    Dyson ring concept drawing (Source: Vedexent/Wikipedia)
    3
    Dyson bubble concept drawing (Source: PNG Crusade Bot/Wikipedia)/CC BY 2.5

    After we’ve been able to harness all the energy from our home planet, we’ll move on to harnessing all the energy of our home star, the sun. One way of doing this is to build a Dyson swarm around the star, or a group of panels capable of reflecting light into small solar power plants which could then send those light beams to Earth for our use. Similar to the work of controlling the forces here on Earth, we’d be able to control the star as well, including the manipulation of solar flares. Another way to get enough energy for a Type II civilization would be to build a fusion reactor on a huge scale or to use a reactor to essentially drain the hydrogen from a nearby gas giant, like Jupiter.

    At this point we’re a few thousand years into the future and using 10²⁶ watts of energy. A stellar civilization capable of gathering energy on this scale has become immune to extinction.

    Type III

    We’ve gone from controlling all the energy of our home planet to our home star and, now, our galaxy. Take the Dyson swarm proposed above and extend it to cover all 100 billion stars of the Milky Way. A civilization this advanced, and with access to this many resources, would truly be a master race, having at their disposal 10³⁶ watts of energy. Hundreds of thousands, even millions of years of evolution would mean that we as a race would look very different, both biologically and in terms of merging with our technology in becoming cyborgs or even fully robotic.

    To colonize all the stars we could use self-replicating robots that would assemble and maintain the Dyson swarms, though it’s likely we’ll have found a new energy source by then. This could include tapping into the energy of the black hole at the center of the Milky Way, or even using gamma ray bursts. Another possibility, though they have been yet undetected, would be to find a white hole and to use the energy that emanates from it.

    The trick for a galactic species would be the constraints of the laws of physics — how can they be united when their colonies are light years away? They’d have to find a way to move at the speed of light or, even better, create wormholes to other locations.

    Kardashev ended the scale here because he didn’t believe it could go any further, stating that any civilizations beyond Type III would be too advanced to even fathom. But other astronomers have since extended the scale to include Type IV and Type V.

    Type IV and V

    A Type IV civilization would be undetectable to us. It would be able to harness the entire energy of the universe and move across all of space, appearing as nothing more than a work of nature. Some speculate that giant voids in space, like the one 1.8 billion light years across and missing 90% of its galaxies, could be proof of a civilization making use of the universe. But a civilization this advanced might not even harness energy as we know it anymore, choosing instead to move into more exotic substances, like dark energy. They might also live inside black holes, controlling 10⁴⁶ watts of energy. These feats are very sci-fi and, as far as we know, impossible to accomplish. But then again we’re a lowly Type 0 civilization with no idea what may lie ahead.

    It gets even more fantastical when one considers a Type V master race that would function like gods, able to harness energy not only from this universe, but all universes in all dimensions. Its energy usage and access to knowledge would be incomprehensible.

    Micro-scale

    The micro-dimensional mastery extension to the Kardashev scale was proposed by John D. Barrow, a scientist who decided to take civilization ranking in the opposite direction, choosing instead to base his scale on how small a people’s control could reach. This scale is outlined differently:

    Type I-minus: controlling matter at the observable level, that is, being to manipulate things we can see and touch.

    Type II-minus: controlling genes

    Type III-minus: controlling molecules

    Type IV-minus: controlling atoms

    Type V-minus: controlling protons

    Type VI-minus: controlling elementary particles, like quarks

    Type Omega-minus: controlling fundamental elements of spacetime

    Whether using the original or micro version, the beautiful thing about the Kardashev scale is that it’s not just full of fascinating and alien concepts; it’s also a blueprint for where we could go if our species could just make it the next 100 years. Will the human race emerge from our planet and thrive in the universe just as we emerged from Africa and grew to thrive around the world?

    See the full article here .

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  • richardmitnick 6:37 am on August 30, 2018 Permalink | Reply
    Tags: , , , Black Hole Firewalls Could Be Too Tepid to Burn, Black Holes, , , ,   

    From Nautilus: “Black Hole Firewalls Could Be Too Tepid to Burn” 

    Nautilus

    From Nautilus

    Aug 29, 2018
    Charlie Wood

    Artist’s conception of two merging black holes similar to those detected by LIGO Credit LIGO-Caltech/MIT/Sonoma State /Aurore Simonnet

    1
    String theorists elide a paradox about black holes by extinguishing the walls of fire feared to surround them. NASA

    Despite its ability to bend both minds and space, an Einsteinian black hole looks so simple a child could draw it. There’s a point in the center, a perfectly spherical boundary a bit farther out, and that’s it

    The point is the singularity, an infinitely dense, unimaginably small dot contorting space so radically that anything nearby falls straight in, leaving behind a vacuum. The spherical boundary marks the event horizon, the point of no return between the vacuum and the rest of the universe. But according to Einstein’s theory of gravity, the event horizon isn’t anything that an unlucky astronaut would immediately notice if she were to cross it. “It’s like the horizon outside your window,” said Samir Mathur, a physicist at Ohio State University. “If you actually walked over there, there’s nothing.”

    In 2012, however, this placid picture went up in flames. A team of four physicists took a puzzle first put forward by Stephen Hawking about what happens to all the information that falls into the black hole, and turned it on its head. Rather than insisting that an astronaut (often named Alice) pass smoothly over the event horizon, they prioritized a key postulate of quantum mechanics: Information, like matter and energy, must never be destroyed. That change ended up promoting the event horizon from mathematical boundary to physical object, one they colorfully named the wall of fire.

    “It can’t be empty, and it turns out it has to be full of a lot of stuff, a lot of hot stuff,” said Donald Marolf, a physicist at the University of California, Santa Barbara, and one of the four co-authors [no cited paper]. The argument caused an uproar in the theoretical physics community, much as if cartographers suggested that instead of an imaginary line on their maps, Earth’s equator was actually a wall of bright red bricks.

    The news of a structure at the boundary didn’t shock Mathur, however. For more than a decade he had been arguing that black holes are really balls of strings (from string theory) with hot, fuzzy surfaces. “As you come closer and closer it gets hotter and hotter, and that’s what causes the burning,” he explained.

    In recent years, Mathur has been refining his “fuzzball” description, and his most recent calculations bring marginally good news for Alice. While she wouldn’t live a long and healthy life, the horizon’s heat might not be what does her in.

    Fuzzballs are what you get when you apply string theory, a description of nature that replaces particles with strings, to extremely dense objects. Energize a particle and it can only speed up, but strings stretch and swell as well. That ability to expand, combined with additional flexibility from postulated extra dimensions, makes strings fluff up when enough of them are packed into a small space. They form a fuzzy ball that looks from afar like an ordinary black hole—it has the same size (for a given mass) and emits the same kind of “Hawking radiation” that all black holes emit. As a bonus, the slightly bumpy surface changes the way it emits particles and declaws Hawking’s information puzzle, according to Mathur. “It’s more like a planet,” he said, “and it radiates from that surface just like anything else.”

    33
    Olena Shmahalo / Quanta Magazine

    His new work extends arguments from 2014, which asked what would happen to Alice if she were to fall onto a supermassive fuzzball akin to the one at the heart of our galaxy—one with the mass of millions of suns. In such situations, the force of gravity dominates all others. Assuming this constraint, Mathur and his collaborator found that an incoming Alice particle had almost no chance of smashing into an outgoing particle of Hawking radiation. The surface might be hot, he said, but the way the fuzzball expands to swallow new material prevents anything from getting close enough to burn, so Alice should make it to the surface.


    In response, Marolf suggested that a medium-size fuzzball might still be able to barbecue Alice in other ways. It wouldn’t drag her in as fast, and in a collision at lower energies, forces other than gravity could singe her, too.

    Mathur’s team recently took a more detailed look at Alice’s experience with new calculations published in the Journal of High Energy Physics. They concluded that for a modest fuzzball—one as massive as our sun—the overall chance of an Alice particle hitting a radiation particle was slightly higher than they had found before, but still very close to zero. Their work suggested that you’d have to shrink a fuzzball down to a thousand times smaller than the nanoscale before burning would become likely.

    By allowing Alice to reach the surface more or less intact (she would still undergo an uncontroversial and likely fatal stretching), the theory might even end up restoring the Einsteinian picture of smooth passage across the boundary, albeit in a twisted form. There might be a scenario in which Alice went splat on the surface while simultaneously feeling as if she were falling through open space, whatever that might mean.

    “If you jump onto [fuzzballs] in one description, you break up into little strings. That’s the splat picture,” Mathur said. We typically assume that once her particles start breaking up, Alice ceases to be Alice. A bizarre duality in string theory, however, allows her strings to spread out across the fuzzball in an orderly way that preserves their connections, and, perhaps, her sense of self. “If you look carefully at what [the strings] are doing,” Mathur continued, “they’re actually spreading in a very coherent ball.”

    The details of Mathur’s picture remain rough. And the model rests entirely on the machinery of string theory, a mathematical framework with no experimental evidence. What’s more, not even string theory can handle the messiness of realistic fuzzballs. Instead, physicists focus on contrived examples such as highly organized, extra-frigid bodies with extreme features, said Marika Taylor, a string theorist at the University of Southampton in the U.K.

    Mathur’s calculations are exploratory, she said, approximate generalizations from the common features of the simple models. The next step is a theory that can describe the fuzzball’s surface at the quantum level, from the point of view of the string. Nevertheless, she agreed that the hot firewall idea has always smelled fishy from a string-theory perspective. “You suddenly transition from ‘I’m falling perfectly happily’ to ‘Oh my God, I’m completely destroyed’? That’s unsatisfactory,” she said.

    Marolf refrained from commenting on the latest results until he finished discussing them with Mathur, but said that he was interested in learning more about how the other forces had been accounted for and how the fuzzball surface would react to Alice’s visit. He also pointed out that Mathur’s black hole model was just one of many tactics for resolving Hawking’s puzzle, and there was no guarantee that anyone had hit on the right one. “Maybe the real world is crazier than even the things we’ve thought of yet,” he said, “and we’re just not being clever enough.”

    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 3:05 pm on August 17, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , ,   

    From Discover Magazine: “Astronomers Find New Way to Supersize Baby Black Holes” 

    DiscoverMag

    From Discover Magazine

    August 16, 2018
    Jake Parks

    1
    This artist’s concept depicts a supermassive black hole surrounded by a dense disk of gas and dust in the center of a galaxy. (Credit: NASA/JPL-Caltech)

    Just last year, three American physicists shared the Nobel Prize in Physics for their role in the historic detection of gravitational waves. The signals came from cosmic ripples in space-time created by some of the most violent events in the universe: colliding black holes.

    Scientists have now detected six gravitational-wave signals — five from merging pairs of stellar-mass black holes, and one from a merging pair of neutron stars. But strangely, most of the stellar-mass black holes involved were more than 20 times as massive as the Sun. The find perplexed astronomers. Stellar-mass black holes, which form when massive stars collapse, typically top out at about 10 to 15 times the mass of the Sun.

    Bulking Up Black Holes

    So, how did these relatively small black holes bulk up before merging?

    In the past, scientists suspected these black holes grew larger because they started their lives as giant stars with very few metals — or elements besides hydrogen and helium. Since low-metallicity stars produce weak solar winds, they keep most of their mass before collapsing into black holes.

    But according to a new study published in The Astrophysical Journal Letters, there may be more than one way to make a black hole balloon in size — and it doesn’t involve a low-metal diet.

    Instead, the authors outline a way that average stellar-mass black hole can grow by gobbling up the material circling a galaxy’s supermassive black hole. Furthermore, this new mechanism also may predict a fresh source of gravitational waves.

    2
    Gravitational waves are produced by the inspiral and eventual merger of two extremely dense objects, such as black holes or neutron stars. This creates ripples in the fabric of space-time that propagate outward at the speed of light. (Credit: R. Hurt/Caltech-JPL)

    Spiraling Disks

    Astronomers know that the majority of large galaxies house supermassive black holes in their cores. Many of these black holes lie dormant for most of their lives, accreting little matter and producing little light.

    However, some supermassive black holes are surrounded by a dense disk of gas and dust that harshly grinds together as it spins inward toward the supermassive black hole itself. This spinning disk generates incredible amounts of friction, which causes the material inside it to glow brightly. If these radiant disks are especially bright, astronomers refer to them as active galactic nuclei, or AGN.

    Just outside these chaotic disks, however, are numerous stars — many of which will eventually evolve into stellar-mass black holes.

    According to the new study, a pair of these nearby stellar-mass black holes can easily become trapped within the AGN’s disk. And when this happens, the black holes feed on the available matter as they spiral ever closer, growing from around seven solar masses to more than 20 solar masses before they eventually merge.

    The gravitational-wave signal generated by such a merger would indicate that the two black holes involved were around 20 solar masses, even though they both initially started much smaller.

    Multi-Messenger Astronomy

    One interesting offshoot of this newly proposed method for forming supersized stellar-mass black holes is that their environment can often cause them to synchronize their spin axes, like two tops spinning in tandem. According to the study, such systems release about 10 percent of their energy as gravitational waves when they do finally merge. That’s as much as three times more gravitational-wave energy than would be released if the black holes were randomly oriented, which means these mergers are likely detectable with current technology, such as the Laser Interferometer Gravitational-wave Observatory (LIGO).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    See also https://sciencesprings.wordpress.com/2017/10/20/from-ucsc-neutron-stars-gravitational-waves-and-all-the-gold-in-the-universe/

    The authors also say these black holes would likely emit large amounts of X-rays, gamma rays, or even radio waves. Those wavelengths could provide an electromagnetic counterpart to a gravitational-wave signal, revealing important details that would otherwise remain hidden.

    Last year, astronomers managed to do just this when they observed both gravitational waves and gamma rays from the merger of two neutron stars. At the time, astronomer Josh Simon of Carnegie Observatories said of the neutron star detection, “There are things you can discover with gravitational waves that you could never see with electromagnetic light, and vice versa. Having that combination should provide us with insights into these extreme objects.”

    What’s Next?

    So, is this newly proposed method for forming supersized stellar-mass black holes the explanation for LIGO’s extra-large detections, or are low-metal stars responsible? Or maybe it’s a combination of both. At this point, we just don’t know for sure.

    However, LIGO and its sister detector Virgo are currently undergoing planned upgrades, and should start observing again in early 2019. And when they kick back on, astronomers will no doubt be hunting for gravitational-wave signals that can be paired with electromagnetic observations. Such multi-messenger detections will likely be key to the future of astronomy, so make sure to stay tuned.

    See the full article here .

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  • richardmitnick 1:33 pm on August 11, 2018 Permalink | Reply
    Tags: , , , Black Holes, , Quasars are now known to be supermassive black holes feeding on surrounding gas not stars., TDEs-Tidal disruption events, , Zwicky Transit Facility at California’s Palomar Observatory   

    From Wired: “Star-Swallowing Black Holes Reveal Secrets in Exotic Light Shows” 

    Wired logo

    From Wired

    08.11.18
    Joshua Sokol

    Black holes, befitting their name and general vibe, are hard to find and harder to study. You can eavesdrop on small ones from the gravitational waves that echo through space when they collide—but that technique is new, and still rare. You can produce laborious maps of stars flitting around the black hole at the center of the Milky Way or nearby galaxies. Or you can watch them gulp down gas clouds, which emit radiation as they fall.

    Now researchers have a new option. They’ve begun corralling ultrabright flashes called tidal disruption events (TDEs), which occur when a large black hole seizes a passing star, shreds it in two and devours much of it with the appetite of a bear snagging a salmon. “To me, it’s sort of like science fiction,” said Enrico Ramirez-Ruiz, an astrophysicist at University of California, Santa Cruz, and the Niels Bohr Institute.

    During the past few years, though, the study of TDEs has transformed from science fiction to a sleepy cottage industry, and now into something more like a bustling tech startup.

    Automated wide-field telescopes that can pan across thousands of galaxies each night have uncovered about two dozen TDEs. Included in these discoveries are some bizarre and long-sought members of the TDE zoo. In June, a study in the journal Nature described an outburst of X-ray light in a cluster of faraway stars that astronomers interpreted as a midsized black hole swallowing a star. That same month, another group announced in Science that they had discovered what may be brightest ever TDE, one that illuminated faint gas at the heart of a pair of merging galaxies.

    These discoveries have taken place as our understanding of what’s really happening during a TDE comes into sharper focus. At the end of May, a group of astrophysicists proposed [The Astrophysical Journal Letters] a new theoretical model for how TDEs work. The model can explain why different TDEs can appear to behave differently, even though the underlying physics is presumably the same.

    Astronomers hope that decoding these exotic light shows will let them conduct a black hole census. Tidal disruptions expose the masses, spins and sheer numbers of black holes in the universe, the vast majority of which would be otherwise invisible. Theorists are hungry, for example, to see if TDEs might unveil any intermediate-mass black holes with weights between the two known black hole classes: star-size black holes that weigh a few times more than the sun, and the million- and billion-solar-mass behemoths that haunt the cores of galaxies. The Nature paper claims they may already have.


    A numerical simulation of the core of a star as it’s being consumed by a black hole. Video by Guillochon and Ramirez-Ruiz

    Researchers have also started to use TDEs to probe the fundamental physics of black holes. They can be used to test whether black holes always have event horizons—curtains beyond which nothing can return—as Einstein’s theory of general relativity predicts.

    Meanwhile, many more observations are on the way. The rate of new TDEs, now about one or two per year, could jump up by an order of magnitude [Stellar Tidal Disruption Events in General Relativity]even by the end of this year because of the Zwicky Transient Facility, which started scanning the sky over California’s Palomar Observatory in March.

    Zwicky Transit Facility at California’s Palomar Observatory schematic

    Zwicky Transit Facility at California’s Palomar Observatory

    And with the addition of planned observatories, it may increase perhaps another order of magnitude in the years to come.Researchers have also started to use TDEs to probe the fundamental physics of black holes. They can be used to test whether black holes always have event horizons—curtains beyond which nothing can return—as Einstein’s theory of general relativity predicts.

    “The field has really blossomed,” said Suvi Gezari at the University of Maryland, one of the few stubborn pioneers who staked their careers on TDEs during leaner years. She now leads the Zwicky Transient Facility’s TDE-hunting team, which has already snagged unpublished candidates in its opening months, she said. “Now people are really digging in.”

    Searching for Star-Taffy

    In 1975, the British physicist Jack Hills first dreamed up a black-hole-eats-star scenario as a way to explain what powers quasars—superbright points of light from the distant universe. (Quasars are now known to be supermassive black holes feeding on surrounding gas, not stars.) But in 1988, the British cosmologist Martin Rees realized [Nature]that black holes snacking on a star would exhibit a sharp flare, not a steady glow. Looking for such flares could let astronomers find and study the black holes themselves, he argued.

    Nothing that fit the bill turned up until the late 1990s. That’s when Stefanie Komossa, at the time a graduate student at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, found massive X-ray flares [Discovery of a giant and luminous X-ray outburst from the optically inactive galaxy pair RXJ1242.6-1119] from the centers of distant galaxies that brightened and dimmed according to the Rees predictions.

    The astronomical community responded to these discoveries—based on just a few data points—with caution. Then in the mid-2000s, Gezari, then beginning a postdoc at the California Institute of Technology, searched for and discovered her own handful of TDE candidates. She looked for flashes of ultraviolet light, not X-rays as Komossa had. “In the old days,” Gezari said, “I was just trying to convince people that any of our discoveries were actually due to a tidal disruption.”

    Soon, though, she had something to sway even the doubters. In 2010, Gezari discovered an especially clear flare, rising and falling as modelers predicted. She published it in Nature in 2012, catching other astronomers’ attention. In the years since, large surveys in optical light, sifting through the sky for changes in brightness, have taken over the hunt. And like Komossa’s and Gezari’s TDEs, which had both been fished out of missions designed to look for other things, the newest batch showed up as bycatch. “It was, oh, why didn’t we think about looking for these?” said Christopher Kochanek, an astrophysicist at Ohio State University who works on a project designed to search for supernovas [ASAS-SN OSU All-Sky Automated Survey for Supernovae].

    Now, with a growing number of TDEs in hand, astrophysicists are within arm’s reach of Rees’s original goal: pinpointing and studying gargantuan black holes. But they still need to learn to interpret these events, divining their basic physics. Unexpectedly, the known TDEs fall into separate classes [A unified model for tidal disruption events]. Some seem to emit mostly ultraviolet and optical light, as if from gas heated to tens of thousands of degrees. Others glow fiercely with X-rays, suggesting temperatures an order of magnitude higher. Yet presumably they all have the same basic physical root.

    To be disrupted, an unlucky star must venture close enough to a black hole that gravitational tides exceed the internal gravity that binds the star together. In other words, the difference in the black hole’s gravitational pull on the near and far sides of the star, along with the inertial pull as the star swings around the black hole, stretches the star out into a stream. “Basically it spaghettifies,” said James Guillochon, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics.

    The outer half of the star escapes away into space. But the inner half—that dense stream of star-taffy—swirls into the black hole, heating up and releasing huge sums of energy that radiate across the universe.

    With this general mechanism understood, researchers had trouble understanding why individual TDEs can look so distinct. One longstanding idea appeals to different phases of the star-eating process. As the star flesh gets initially torn away and stretched into a stream, it might ricochet around the black hole and slam into its own tail. This process might heat the tail up to ultraviolet-producing temperatures—but not hotter. Then later—after a few months or a year—the star would settle into an accretion disk, a fat bagel of spinning gas that theories predict should be hot enough to emit X-rays.

    See the full article here .


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  • richardmitnick 6:58 pm on July 26, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , ,   

    From Discover Magazine: “Secrets Of The Strange Stars That Circle Our Supermassive Black Hole” 

    DiscoverMag

    From Discover Magazine

    1
    This artist’s illustration shows the supermassive black hole lurking at the center of our spiral galaxy, the Milky Way. (Credit: NASA/CXC/M.Weiss)

    NASA/Chandra X-ray Telescope

    High winds are the norm at the center of the Milky Way. Astronomers have now clocked suns orbiting the galactic core at a staggering 3,000 miles (4,800 kilometers) per second. At this rate, Earth would complete its orbit around the sun in a mere three days. What lurks at the galaxy’s core that can accelerate stars to such speeds?

    Astronomers have considered various possibilities. Does the center of the galaxy harbor a tight cluster of superdense stellar remnants (neutron stars)? Or perhaps a huge ball of subatomic neutrino particles?

    But these and other more exotic possibilities were eliminated in the spring of 2002 when a star called S2 swept down in its highly eccentric orbit and passed within 17 light-hours of the Milky Way’s center — a minuscule distance in galactic terms. In 17 hours, light travels three times the distance between Pluto and the sun.

    Only one object is compact enough and has sufficient mass to accelerate stars to such a high speed: a supermassive black hole. Astronomers had suspected that a black hole must lie at the Milky Way’s core, but plotting the orbit of S2 and other stars dramatically strengthened the evidence.

    SO-2 Image UCLA Galactic Center Groupe via S. Sakai and Andrea Ghez at Keck Observatory

    Our central black hole is small by the standard of what lurks in the hearts of other galaxies. Observations of the giant elliptical galaxy Messier 87 suggest the presence of a black hole 6 billion times more massive than the sun. The interaction of two supermassive black holes probably produces the intense X-rays streaming from the galaxy NGC 6240. The Andromeda Galaxy may harbor a black hole of 140 million solar masses.

    Andromeda Galaxy Adam Evans

    In comparison, our galaxy’s black hole is paltry — containing about 4 million solar masses. But its nearness means we can study it in detail, including charting the orbits of dozens of stars buzzing around it like bees. The stellar-mass black holes found in some binary star systems are too small to be observed in detail by telescopes anytime soon. So, the best chance of seeing what happens in the bizarre neighborhood around a black hole is to study the one at the Milky Way’s heart. So far, it has not failed to surprise us.

    2
    Bright stars surround the supermassive black hole at the Milky Way’s center. (Credit: NASA/CXC/M.Weiss)

    The Inner Realm

    The galactic center lies about 26,000 lightyears from Earth toward the constellation Sagittarius. It is a region of the sky where bright stars mingle with dark clouds of gas and dust. The actual center is too obscured to reveal much when astronomers observe it in visible light. What we know of it comes from data collected in infrared and radio wavelengths. These wavelengths can pass through the dust and gas and reach Earth-based telescopes.

    Astronomers have long known that the strongest source of radio energy in the sky, after the sun, lies at the galactic center. This broad core region is called Sagittarius A, often abbreviated as Sgr A.

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

    Sgr A hosts dozens of individual radio sources. One is called Sagittarius A*, pronounced “Sagittarius A star.” It lies at the very center of the galaxy and coincides with the position of the supermassive black hole. Everything else rotates clockwise (from Earth’s point of view) around this point, making it the dynamic center of the galaxy. And it is a very busy neighborhood.

    Surrounding Sgr A* at a distance of several light-years, a shell of dust rotates counterclockwise — opposite to the galaxy’s general rotation. Lying inside the shell, and turning in the same direction, is a small spiral structure with three arms.

    Each arm is a stream of hot gas set aglow by nearby stars. The gas flows toward the center of the spiral where Sgr A* lies. Radio images taken a few years apart revealed the spiral is rotating. More recently, a close-up look at Sgr A* with new imaging technology has revealed the amazingly powerful gravity of the object the spiral encircles.

    Stellar Raceway

    In 2002, a team of astronomers led by Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, published the first scientific paper announcing S2’s 17-light-hour close encounter with Sgr A*. Using the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile, Genzel’s group caught S2 as it rounded Sgr A* at a fantastic speed. The VLT’s adaptive optics reduces atmospheric blurring, allowing astronomers to chart S2’s position more accurately.

    ESO VLT at Cerro Paranal in the Atacama Desert, elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    For the previous decade, the astronomers had been plotting S2’s orbit, mostly with ESO’s 3.6-meter New Technology Telescope, also in Chile.


    ESO/NTT at Cerro La Silla, Chile, at an altitude of 2400 metres


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

    The orbital positions allowed the researchers to calculate S2’s orbital period around Sgr A* as about 16 years. The orbit is quite eccentric. The star swoops in to within 17 light-hours at its closest approach to Sgr A*, but then sweeps outward to a distance of some 10 light-days at its farthest point. To produce such an orbit requires a compact black hole with about 4 million solar masses.

    Genzel and his colleagues were not the only ones tracking S2 and the many other stars zipping around Sgr A*. Astronomer Andrea Ghez’s Galactic Center Group at UCLA has studied S2 and its motions with the 10-meter Keck Telescope in Hawaii.


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level, showing also NASA’s IRTF and NAOJ Subaru

    In 2000, the team reported evidence that S2’s path is curved — early evidence S2 is orbiting something at the galactic center. The UCLA team later discovered S2’s close orbital distance to Sgr A* at about the same time as Genzel and his colleagues.

    Extensive observations in recent years by Genzel, Ghez, and others paint a fascinating picture of the flurry of activity around Sgr A*. One of the most challenging observations astronomers have performed on the galactic center stars is spectroscopy, or separating starlight into its component wavelengths. A spectrum reveals much about a star’s composition, age, and mass.

    Gathering enough light from a distant star to take a good spectrum requires tracking the target through a narrow slit for many hours. Any small shift in the slit’s position contaminates the spectrum with light from other sources. Spectroscopy is especially challenging in the crowded star field around Sgr A*, where the density of stars is more than a million times higher than in our stellar neighborhood.

    In 2003, Ghez took a spectrum of S2 with the Keck Telescope using its adaptive optics system. The slit trained on the star was only 0.04 inch (1 millimeter) wide. Keeping this narrow gap locked on S2 was like aiming a gun sight on an object the size of a basketball 1,000 miles (1,600 km) away.

    The spectrum revealed S2 to be a heavyweight star some 15 times the sun’s mass. Such large stars exhaust their hydrogen supply quickly — in this case, in less than 10 million years. That means S2 must be younger than 10 million years. In addition, the star has a very hot atmosphere, as do other stars orbiting close to Sgr A*. This also indicates a relatively young age.

    In short, these stars formed 3 to 6 million years ago. This raises a major problem: Why are such young stars orbiting so close to Sgr A*, a region of intense magnetic fields and strong gravitational forces that would normally prevent star formation?

    3
    Radio astronomy reveals hidden features of the Milky Way’s center, including remnants of supernova explosions and stars forming in vast clouds of gas and dust. (Credit: W.M. Goss/C. Lang/VLA/NRAO)

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

    Stellar Masquerade

    One possible explanation is that S2 and its companions may be old stars masquerading as young ones — “a phenomenon we understand quite well in Los Angeles,” Ghez once quipped to a science reporter.

    In this case, what seem to be young stars are actually the cores of older suns that collided and merged. The collisions could have stripped away the suns’ cool outer layers, exposing their hot interiors. The result would be a cluster of massive stars that appear much younger than they really are.

    But there’s a problem with this scenario. A collision violent enough to strip away the outer layers should also annihilate both stars and leave only a trail of hot gas. And so astronomers have proposed alternatives. For example, perhaps the stars formed elsewhere and migrated inward under the black hole’s gravitational pull.

    The problem with this explanation is that most active star formation in the Milky Way occurs far from the core, in its spiral arms. It would take the stars too long to migrate as close to the center as S2.

    Dense dust clouds do lie closer to Sgr A* than the spiral arms, to within a few dozen light-years. Stars are probably forming inside of them. It’s conceivable that a cluster of young stars could spiral down to within a few light-years of the center — and do so in less than 10 million years.

    The problem here is that to get closer to the black hole, the stars would have to shed angular momentum — the quantity that keeps planets in nice safe orbits around stars instead of “falling” directly into them.

    One way to lose angular momentum is to bump into other stars. But it’s difficult to imagine how stars could endure this process and migrate to within light-hours of Sgr A* without being destroyed. Besides, the process should leave behind a trail of stars toward Sgr A* for a long distance, something astronomers have not yet seen. Instead, the shell of stars orbiting close to Sgr A* has a definite outer edge.

    Star Birth in a Disk

    Another possibility is that Sgr A*’s central cluster stars formed within a rotating disk of gas and dust immediately surrounding the black hole. In fact, some observations suggest most stars in the central cluster orbit roughly in the same plane — an arrangement reminiscent of the major planets in our solar system. The planets formed in a disk of gas and dust, so perhaps S2 and its fellow travelers did, too.

    However, not all astronomers agree the central cluster has a disklike structure. Another caveat: To spawn stars, the disk would need to be dense enough to withstand the black hole’s tidal forces.

    It’s also conceivable that Sgr A*’s companion stars formed in dust clouds circling at high speed within a few light-years of the galactic center. Collisions between the clouds could have spawned shock waves, triggering star formation. As the result of collisions between the clouds, they and the new stars embedded within them could have shed enough momentum to settle into orbits around the black hole. The galactic core’s strong magnetic field would have gradually swept the leftover interstellar dust and gas away from the black hole. What would remain is a disk of young stars in close orbit to Sgr A*.

    This scenario explains much of what astronomers see in the galactic core, although not all. UCLA astronomer Brad Hansen thinks he has a viable alternative: Hot young stars now orbit the Milky Way’s central black hole because a second smaller black hole dragged them there.

    The process begins in a crowded young star cluster, dozens of light-years from the galactic center. Collisions between big stars in the cluster’s core form an intermediate-sized black hole in the range of 1,000 to 10,000 solar masses. Gradually, the black hole would migrate toward the galactic center, dragging its cargo of “hostage stars” along with it. Hansen argues this is the only way to quickly transport massive young stars into the galactic center from an outside star-birth location.

    All the black-hole ferry scenario lacks is hard evidence to support it. If a second black hole orbits the primary black hole in the galactic core, its presence might be detectable. Its tug on Sgr A* might cause a detectable wiggle. Clearly, astronomers still have a lot of work left to fully understand the processes at work in the galactic core.

    4
    Dozens of young stars orbit at high speeds around the galaxy’s central black hole. By plotting the stars’ positions for years, astronomers calculated their orbits and estimated the mass of the black hole they encircle. (Credit: Astronomy: Jay Smith, after Andrea Ghez (UCLA))

    Imaging The Black Hole

    Fast-moving stars like S2 remain the best evidence that a black hole lies at the heart of the Milky Way. Other support includes periodic bursts of infrared light from Sgr A*. The bursts suggest the black hole spins, completing a turn every 17 minutes. Astronomers have also detected strong radio pulses coming from Sgr A*. This may indicate that packets of ultra-hot gas and dust are falling into the black hole.

    But this is all still circumstantial evidence. The definitive proof might come if astronomers could actually image the black hole’s edge or “event horizon,” beyond which no light or matter can escape.

    Radio energy passes through the veil of obscuring dust and gas around the galactic center, providing a way to directly image a black hole. By itself, a black hole is essentially invisible. But it would be detectable as a silhouette against the accretion disk of gas spiraling into it. The gas emits energy as it accelerates to high speeds around the black hole.

    Light follows a highly curved path near a black hole, making its silhouette appear wider than it actually is. Bright rings or arcs, formed as the black hole bends or “lenses” light from background sources, might protrude from the silhouette’s edges.

    In 2008, radio astronomers announced an important milestone in the study of our galaxy’s black hole. By combining the power of three radio telescopes, researchers detected features around Sgr A* as small as 31 million miles (50 million km) across. The study found that radio emission from Sgr A* is offset from the black hole, perhaps because it comes from an accretion disk. Astronomers hope the Event Horizon Telescope — a nearly Earth-sized radio observatory comprising about a dozen separate instruments — will be able to image the black hole’s silhouette in the next few years.

    Whatever the result, imaging the Milky Way’s central black hole will put the existence of black holes on a firmer footing and perhaps reveal important new insights about the evolution of galactic cores. A failure to see it will bring into question what we understand about the heart of our own galaxy — including the origins of the highspeed roller derby of young stars whizzing around its center.

    See the full article here .

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  • richardmitnick 1:03 am on May 13, 2018 Permalink | Reply
    Tags: Black Holes, ,   

    From Michigan State University: “Black holes aren’t totally black, and other insights from Stephen Hawking’s groundbreaking work” 

    Michigan State Bloc

    From Michigan State University

    May 8, 2018
    Chris Adami Microbiology and Molecular Genetics; Physics and Astronomy office
    (517) 884-5068
    adami@msu.edu

    1
    No image caption or credit.

    1
    What goes in doesn’t go out? NASA Goddard, CC BY Christoph Adami, Michigan State University

    Mathematical physicist and cosmologist Stephen Hawking was best known for his work exploring the relationship between black holes and quantum physics. A black hole is the remnant of a dying supermassive star that’s fallen into itself; these remnants contract to such a small size that gravity is so strong even light cannot escape from them. Black holes loom large in the popular imagination – schoolchildren ponder why the whole universe doesn’t collapse into one. But Hawking’s careful theoretical work filled in some of the holes in physicists’ knowledge about black holes.

    Why do black holes exist?

    The short answer is: Because gravity exists, and the speed of light is not infinite.

    Imagine you stand on Earth’s surface, and fire a bullet into the air at an angle. Your standard bullet will come back down, someplace farther away. Suppose you have a very powerful rifle. Then you may be able to shoot the bullet at such a speed that, rather than coming down far away, it will instead “miss” the Earth. Continually falling, and continually missing the surface, the bullet will actually be in an orbit around Earth. If your rifle is even stronger, the bullet may be so fast that it leaves Earth’s gravity altogether. This is essentially what happens when we send rockets to Mars, for example.

    Now imagine that gravity is much, much stronger. No rifle could accelerate bullets enough to leave that planet, so instead you decide to shoot light. While photons (the particles of light) do not have mass, they are still influenced by gravity, bending their path just as a bullet’s trajectory is bent by gravity. Even the heaviest of planets won’t have gravity strong enough to bend the photon’s path enough to prevent it from escaping.

    But black holes are not like planets or stars, they are the remnants of stars, packed into the smallest of spheres, say, just a few kilometers in radius. Imagine you could stand on the surface of a black hole, armed with your ray gun. You shoot upwards at an angle and notice that the light ray instead curves, comes down and misses the surface! Now the ray is in an “orbit” around the black hole, at a distance roughly what cosmologists call the Schwarzschild radius, the “point of no return.”

    Thus, as not even light can escape from where you stand, the object you inhabit (if you could) would look completely black to someone looking at it from far away: a black hole.

    3
    Hawking worked to popularize his cosmological insights. AP Photo/Keystone, Salvatore Di Nolfi

    But Hawking discovered that black holes aren’t completely black?

    The short answer is: Yes.

    My previous description of black holes used the language of classical physics – basically, Newton’s theory applied to light. But the laws of physics are actually more complicated because the universe is more complicated.

    In classical physics, the word “vacuum” means the total and complete absence of any form of matter or radiation. But in quantum physics, the vacuum is much more interesting, in particular when it is near a black hole. Rather than being empty, the vacuum is teeming with particle-antiparticle pairs that are created fleetingly by the vacuum’s energy, but must annihilate each other shortly thereafter and return their energy to the vacuum.

    You will find all kinds of particle-antiparticle pairs produced, but the heavier ones occur much more rarely. It’s easiest to produce photon pairs because they have no mass. The photons must always be produced in pairs so they’re moving away from each other and don’t violate the law of momentum conservation.

    3
    No light can be seen coming from a black hole outside the Schwarzschild radius. SubstituteR, CC BY-SA

    Now imagine that a pair is created just at that distance from the center of the black hole where the “last light ray” is circulating: the Schwarzschild radius. This distance could be far from the surface or close, depending on how much mass the black hole has. And imagine that the photon pair is created so that one of the two is pointing inward – toward you, at the center of the black hole, holding your ray gun. The other photon is pointing outward. (By the way, you’d likely be crushed by gravity if you tried this maneuver, but let’s assume you’re superhuman.)

    4
    A pair of photons that annihilate each other is labeled A. In a second pair of photons, labeled B, one enters the black hole while the other heads outward, setting up an energy debt that is paid by the black hole. Christoph Adami, CC BY-ND

    Now there’s a problem: The one photon that moved inside the black hole cannot come back out, because it’s already moving at the speed of light. The photon pair cannot annihilate each other again and pay back their energy to the vacuum that surrounds the black hole. But somebody must pay the piper and this will have to be the black hole itself. After it has welcomed the photon into its land of no return, the black hole must return some of its mass back to the universe: the exact same amount of mass as the energy the pair of photons “borrowed,” according to Einstein’s famous equality E=mc².

    This is essentially what Hawking showed mathematically. The photon that is leaving the black hole horizon will make it look as if the black hole had a faint glow: the Hawking radiation named after him. At the same time he reasoned that if this happens a lot, for a long time, the black hole might lose so much mass that it could disappear altogether (or more precisely, become visible again).

    Do black holes make information disappear forever?

    Short answer: No, that would be against the law.

    Many physicists began worrying about this question shortly after Hawking’s discovery of the glow. The concern is this: The fundamental laws of physics guarantee that every process that happens “forward in time,” can also happen “backwards in time.”

    This seems counter to our intuition, where a melon that splattered on the floor would never magically reassemble itself. But what happens to big objects like melons is really dictated by the laws of statistics. For the melon to reassemble itself, many gazillions of atomic particles would have to do the same thing backwards, and the likelihood of that is essentially zero. But for a single particle this is no problem at all. So for atomic things, everything you observe forwards could just as likely occur backwards.

    Now imagine that you shoot one of two photons into the black hole. They only differ by a marker that we can measure, but that does not affect the energy of the photon (this is called a “polarization”). Let’s call these “left photons” or “right photons.” After the left or right photon crosses the horizon, the black hole changes (it now has more energy), but it changes in the same way whether the left or right photon was absorbed.

    Two different histories now have become one future, and such a future cannot be reversed: How would the laws of physics know which of the two pasts to choose? Left or right? That is the violation of time-reversal invariance. The law requires that every past must have exactly one future, and every future exactly one past.

    Some physicists thought that maybe the Hawking radiation carries an imprint of left/right so as to give an outside observer a hint at what the past was, but no. The Hawking radiation comes from that flickering vacuum surrounding the black hole, and has nothing to do with what you throw in. All seems lost, but not so fast.

    In 1917, Albert Einstein showed that matter (even the vacuum next to matter) actually does react to incoming stuff, in a very peculiar way. The vacuum next to that matter is “tickled” to produce a particle-antiparticle pair that looks like an exact copy of what just came in. In a very real sense, the incoming particle stimulates the matter to create a pair of copies of itself – actually a copy and an anti-copy. Remember, random pairs of particle and antiparticle are created in the vacuum all the time, but the tickled-pairs are not random at all: They look just like the tickler.

    This copy process is known as the “stimulated emission” effect and is at the origin of all lasers. The Hawking glow of black holes, on the other hand, is just what Einstein called the “spontaneous emission” effect, taking place near a black hole.

    Now imagine that the tickling creates this copy, so that the left photon tickles a left photon pair, and a right photon gives a right photon pair. Since one partner of the tickled pairs must stay outside the black hole (again from momentum conservation), that particle creates the “memory” that is needed so that information is preserved: One past has only one future, time can be reversed, and the laws of physics are safe.

    In a cosmic accident, Hawking died on Einstein’s birthday, whose theory of light – it just so happens – saves Hawking’s theory of black holes.

    See the full article here .

    Please help promote STEM in your local schools.

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    Michigan State Campus

    Michigan State University (MSU) is a public research university located in East Lansing, Michigan, United States. MSU was founded in 1855 and became the nation’s first land-grant institution under the Morrill Act of 1862, serving as a model for future land-grant universities.

    MSU pioneered the studies of packaging, hospitality business, plant biology, supply chain management, and telecommunication. U.S. News & World Report ranks several MSU graduate programs in the nation’s top 10, including industrial and organizational psychology, osteopathic medicine, and veterinary medicine, and identifies its graduate programs in elementary education, secondary education, and nuclear physics as the best in the country. MSU has been labeled one of the “Public Ivies,” a publicly funded university considered as providing a quality of education comparable to those of the Ivy League.

    Following the introduction of the Morrill Act, the college became coeducational and expanded its curriculum beyond agriculture. Today, MSU is the seventh-largest university in the United States (in terms of enrollment), with over 49,000 students and 2,950 faculty members. There are approximately 532,000 living MSU alumni worldwide.

     
  • richardmitnick 12:50 pm on April 28, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , , , , Thermodynamics   

    From Kavli Institute for the Physics and Mathematics of the Universe: “Study Finds Way to Use Quantum Entanglement to Study Black Holes” 

    KavliFoundation

    The Kavli Foundation

    Kavli IPMU
    Kavli IMPU

    April 23, 2018

    A team of researchers has found a relationship between quantum physics, the study of very tiny phenomena, to thermodynamics, the study of very large phenomena, reports a new study this week in Nature Communications.

    “Our function can describe a variety of systems from quantum states in electrons to, in principle, black holes,” says study author Masataka Watanabe.

    Quantum entanglement is a phenomenon fundamental to quantum mechanics, where two separated regions share the same information. It is invaluable to a variety of applications including being used as a resource in quantum computation, or quantifying the amount of information stored in a black hole.

    Quantum mechanics is known to preserve information, while thermal equilibrium seems to lose some part of it, and so understanding the relationship between these microscopic and macroscopic concepts is important. So a group of graduate students and a researcher at the University of Tokyo, including the Kavli Institute for the Physics and Mathematics of the Universe, investigated the role of the quantum entanglement in thermal equilibrium in an isolated quantum system.

    1
    Figure 1: Graph showing quantum entanglement and spatial distribution. When separating matter A and B, the vertical axis shows how much quantum entanglement there is, while the horizontal axis shows the length of matter A. (Credit: Nakagawa et al.)

    “A pure quantum state stabilizing into thermal equilibrium can be compared to water being poured into a cup. In a quantum-mechanical system, the colliding water molecules create quantum entanglements, and these quantum entanglements will eventually lead a cup of water to thermal equilibrium. However, it has been a challenge to develop a theory which predicts how much quantum entanglement was inside because lots of quantum entanglements are created in complicated manners at thermal equilibrium,” says Watanabe.

    In their study, the team identified a function predicting the spatial distribution of information stored in an equilibrated system, and they revealed that it was determined by thermodynamic entropy alone. Also, by carrying out computer simulations, they found that the spatial distribution remained the same regardless of what systems were used and regardless of how they reached thermal equilibrium.

    See the full article here .

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    Kavli IPMU (Kavli Institute for the Physics and Mathematics of the Universe) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/
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    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
  • richardmitnick 3:24 pm on April 22, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , Is Dark Matter Made of Primordial Black Holes?   

    From Center For Astrophysics: “Is Dark Matter Made of Primordial Black Holes?” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    1
    The dwarf irregular galaxy IC1613. Astronomers wondering whether primordial black holes might compose the dark matter in the universe suggest that the shapes of faint dwarf galaxies with dark matter halos might reveal the answer. NASA/JPL-Caltech/SSC

    Astronomers studying the motions of galaxies and the character of the cosmic microwave background radiation came to realize in the last century that most of the matter in the universe was not visible.

    Cosmic Background Radiation per Planck

    ESA/Planck 2009 to 2013

    About 84% of the matter in the cosmos is dark matter, much of it located in halos around galaxies.

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    Dark matter halo. Image credit: Virgo consortium / A. Amblard / ESA

    Milky Way Dark Matter Halo Credit ESO L. Calçada

    It was dubbed dark matter because it does not emit light, but it is also mysterious: it is not composed of atoms or their usual constituents like electrons and protons.

    Meanwhile, astronomers have observed the effects of black holes and recently even detected gravitational waves from a pair of merging black holes.

    Artist’s conception of two merging black holes similar to those detected by LIGO Credit LIGO-Caltech/MIT/Sonoma State /Aurore Simonnet

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Black holes usually are formed in the explosive death of massive stars, a process that can take many hundreds of millions of years as a star coalesces from ambient gas, evolves and finally dies. Some black holes are inferred to exist in the early universe, but there is probably is not enough time in the early universe for the normal formation process to occur. Some alternative methods have been proposed, like the direct collapse of primordial gas or processes associated with cosmic inflation, and many of these primordial black holes could have been made.

    CfA astronomer Qirong Zhu led a group of four scientists investigating the possibility that today’s dark matter is composed of primordial black holes, following up on previously published suggestions. If galaxy halos are made of black holes, they should have a different density distribution than halos made of exotic particles. There are some other differences as well – black hole halos are expected to form earlier in a galaxy’s evolution than do some other kinds of halos. The scientists suggest that looking at the stars in the halos of faint dwarf galaxies can probe these effects because dwarf galaxies are small and faint (they shine with a mere few thousand solar luminosities) where slight effects can be more easily spotted. The team ran a set of computer simulations to test whether dwarf galaxy halos might reveal the presence of primordial black holes, and they find that they could: interactions between stars and primordial halo black holes should slightly alter the sizes of the stellar distributions. The astronomers also conclude that such black holes would need to have masses between about two and fourteen solar masses, right in the expected range for these exotic objects (although smaller than the black holes recently spotted by gravitational wave detectors) and comparable to the conclusions of other studies. The team emphasizes, however, that all the models are still inconclusive and the nature of dark matter remains elusive.

    Science paper:
    Qirong Zhu, Eugene Vasiliev, Yuexing Li, and Yipeng Jing,
    Primordial Black Holes as Dark Matter: Constraints from Compact Ultra-faint Dwarfs
    MNRAS

    See the full article here .

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

     
  • richardmitnick 11:02 am on April 11, 2018 Permalink | Reply
    Tags: , , , Black Holes, , Dense stellar clusters may foster black hole megamergers, ,   

    From Kavli MIT Institute For Astrophysics and Space Research: “Dense stellar clusters may foster black hole megamergers” 

    KavliFoundation

    http://www.kavlifoundation.org/institutes

    Kavli MIT Institute of Astrophysics and Space Research

    Kavli MIT Institute For Astrophysics and Space Research

    April 10, 2018
    Jennifer Chu

    When LIGO’s twin detectors first picked up faint wobbles in their respective, identical mirrors, the signal didn’t just provide first direct detection of gravitational waves — it also confirmed the existence of stellar binary black holes, which gave rise to the signal in the first place.

    1
    A snapshot of a simulation showing a binary black hole formed in the center of a dense star cluster. Credit: Northwestern Visualization/Carl Rodriguez. https://phys.org

    2
    A simulation showing an encounter between a binary black hole (in orange) and a single black hole (in blue) with relativistic effects. Eventually two black holes emit a burst of gravitational waves and merge, creating a new black hole (in red). Credit: Massachusetts Institute of Technology. https://phys.org


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Stellar binary black holes are formed when two black holes, created out of the remnants of massive stars, begin to orbit each other. Eventually, the black holes merge in a spectacular collision that, according to Einstein’s theory of general relativity, should release a huge amount of energy in the form of gravitational waves.

    Now, an international team led by MIT astrophysicist Carl Rodriguez suggests that black holes may partner up and merge multiple times, producing black holes more massive than those that form from single stars. These “second-generation mergers” should come from globular clusters — small regions of space, usually at the edges of a galaxy, that are packed with hundreds of thousands to millions of stars.

    “We think these clusters formed with hundreds to thousands of black holes that rapidly sank down in the center,” says Carl Rodriguez, a Pappalardo fellow in MIT’s Department of Physics and the Kavli Institute for Astrophysics and Space Research. “These kinds of clusters are essentially factories for black hole binaries, where you’ve got so many black holes hanging out in a small region of space that two black holes could merge and produce a more massive black hole. Then that new black hole can find another companion and merge again.”

    If LIGO detects a binary with a black hole component whose mass is greater than around 50 solar masses, then according to the group’s results, there’s a good chance that object arose not from individual stars, but from a dense stellar cluster.

    “If we wait long enough, then eventually LIGO will see something that could only have come from these star clusters, because it would be bigger than anything you could get from a single star,” Rodriguez says.

    He and his colleagues report their results in a paper appearing in Physical Review Letters.

    Running stars

    For the past several years, Rodriguez has investigated the behavior of black holes within globular clusters and whether their interactions differ from black holes occupying less populated regions in space.

    Globular clusters can be found in most galaxies, and their number scales with a galaxy’s size. Huge, elliptical galaxies, for instance, host tens of thousands of these stellar conglomerations, while our own Milky Way holds about 200, with the closest cluster residing about 7,000 light years from Earth.

    In their new paper, Rodriguez and his colleagues report using a supercomputer called Quest, at Northwestern University, to simulate the complex, dynamical interactions within 24 stellar clusters, ranging in size from 200,000 to 2 million stars, and covering a range of different densities and metallic compositions. The simulations model the evolution of individual stars within these clusters over 12 billion years, following their interactions with other stars and, ultimately, the formation and evolution of the black holes. The simulations also model the trajectories of black holes once they form.

    “The neat thing is, because black holes are the most massive objects in these clusters, they sink to the center, where you get a high enough density of black holes to form binaries,” Rodriguez says. “Binary black holes are basically like giant targets hanging out in the cluster, and as you throw other black holes or stars at them, they undergo these crazy chaotic encounters.”

    It’s all relative

    When running their simulations, the researchers added a key ingredient that was missing in previous efforts to simulate globular clusters.

    “What people had done in the past was to treat this as a purely Newtonian problem,” Rodriguez says. “Newton’s theory of gravity works in 99.9 percent of all cases. The few cases in which it doesn’t work might be when you have two black holes whizzing by each other very closely, which normally doesn’t happen in most galaxies.”

    Newton’s theory of relativity assumes that, if the black holes were unbound to begin with, neither one would affect the other, and they would simply pass each other by, unchanged. This line of reasoning stems from the fact that Newton failed to recognize the existence of gravitational waves — which Einstein much later predicted would arise from massive orbiting objects, such as two black holes in close proximity.

    “In Einstein’s theory of general relativity, where I can emit gravitational waves, then when one black hole passes near another, it can actually emit a tiny pulse of gravitational waves,” Rodriguez explains. “This can subtract enough energy from the system that the two black holes actually become bound, and then they will rapidly merge.”

    The team decided to add Einstein’s relativistic effects into their simulations of globular clusters. After running the simulations, they observed black holes merging with each other to create new black holes, inside the stellar clusters themselves. Without relativistic effects, Newtonian gravity predicts that most binary black holes would be kicked out of the cluster by other black holes before they could merge. But by taking relativistic effects into account, Rodriguez and his colleagues found that nearly half of the binary black holes merged inside their stellar clusters, creating a new generation of black holes more massive than those formed from the stars. What happens to those new black holes inside the cluster is a matter of spin.

    “If the two black holes are spinning when they merge, the black hole they create will emit gravitational waves in a single preferred direction, like a rocket, creating a new black hole that can shoot out as fast as 5,000 kilometers per second — so, insanely fast,” Rodriguez says. “It only takes a kick of maybe a few tens to a hundred kilometers per second to escape one of these clusters.”

    Because of this effect, scientists have largely figured that the product of any black hole merger would get kicked out of the cluster, since it was assumed that most black holes are rapidly spinning.

    This assumption, however, seems to contradict the measurements from LIGO, which has so far only detected binary black holes with low spins. To test the implications of this, Rodriguez dialed down the spins of the black holes in his simulations and found that in this scenario, nearly 20 percent of binary black holes from clusters had at least one black hole that was formed in a previous merger. Because they were formed from other black holes, some of these second-generation black holes can be in the range of 50 to 130 solar masses. Scientists believe black holes of this mass cannot form from a single star.

    Rodriguez says that if gravitational-wave telescopes such as LIGO detect an object with a mass within this range, there is a good chance that it came not from a single collapsing star, but from a dense stellar cluster.

    “My co-authors and I have a bet against a couple people studying binary star formation that within the first 100 LIGO detections, LIGO will detect something within this upper mass gap,” Rodriguez says. “I get a nice bottle of wine if that happens to be true.”

    This research was supported in part by the MIT Pappalardo Fellowship in Physics, NASA, the National Science Foundation, the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) at Northwestern University, the Institute of Space Sciences (ICE, CSIC) and Institut d’Estudis Espacials de Catalunya (IEEC), and the Tata Institute of Fundamental Research in Mumbai, India.

    See the full article here .

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    Mission Statement

    The mission of the MIT Kavli Institute (MKI) for Astrophysics and Space Research is to facilitate and carry out the research programs of faculty and research staff whose interests lie in the broadly defined area of astrophysics and space research. Specifically, the MKI will

    Provide an intellectual home for faculty, research staff, and students engaged in space- and ground-based astrophysics
    Develop and operate space- and ground-based instrumentation for astrophysics
    Engage in technology development
    Maintain an engineering and technical core capability for enabling and supporting innovative research
    Communicate to students, educators, and the public an understanding of and an appreciation for the goals, techniques and results of MKI’s research.

    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
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