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

    DiscoverMag

    From Discover Magazine

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    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.

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    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” 

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    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 .

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    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/
    Stem Education Coalition
    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.

     
  • richardmitnick 5:02 pm on March 28, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , , UMASSD Professor overturns understanding on black holes   

    From UMass Dartmouth: “Professor overturns understanding on black holes” 

    UMass Dartmouth

    March 28, 2018
    Office of Public Affairs

    Dr. Gaurav Khanna, Ph.D. publishes a paper that sheds new light on space’s most mysterious phenomena.

    1

    On March 29, 2018, the Physical Review journal [Physical Review D] is set to publish an article by Professors Gaurav Khanna (Physics) of UMass Dartmouth and Lior Burko of Georgia Gwinnett College that demonstrates the existence of extreme black holes that until now were thought to be theoretical and unobservable. “These findings could open the door to new paths of research related to the nature of the universe,” said Khanna.

    Extreme black holes differ from traditional black holes because they have the fastest possible spin allowed by Einstein’s theory of relativity. Khanna and Burko’s research upends conventional wisdom on extreme black holes, which presumed these objects were unstable, and thus did not exist in nature. Through computational research, Khanna and Burko found that extreme black holes are stable and may someday be observed by gravitational-wave observatories.

    Dr. Khanna has a long history of studying these fascinating cosmic objects. In 2015, the universe’s gravitational waves were observed for the very first time by 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)

    This led to a Novel Prize in Physics for the three leaders of the LIGO project. The LIGO project is a collaboration of over 1,000 researchers from more than 20 countries. The UMass Dartmouth Physics Department has had a long relationship with the LIGO project extending over a decade. Physics majors have participated in summer internships at the LIGO laboratory, and others have officially joined the LIGO collaboration later in their careers.

    One of the Nobel winners visited the university in 2016 to discuss his work and Dr. Khanna presented a seminar on this groundbreaking discovery.

    UMass Dartmouth has a strong focus on the cosmos. Recently, astronaut alumnus Scott Tingle (College of Engineering ’87) participated in a satellite downlink event where he answered questions live from the International Space Station. This was preceded by a faculty panel that discussed various perspectives on life in space.

    See the full article here .

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    Mission Statement

    UMass Dartmouth distinguishes itself as a vibrant, public research university dedicated to engaged learning and innovative research resulting in personal and lifelong student success. The University serves as an intellectual catalyst for economic, social, and cultural transformation on a global, national, and regional scale.
    Vision Statement

    UMass Dartmouth will be a globally recognized premier research university committed to inclusion, access, advancement of knowledge, student success, and community engagement.

    The University of Massachusetts Dartmouth (UMass Dartmouth or UMassD) is one of five campuses and operating subdivisions of the University of Massachusetts. It is located in North Dartmouth, Massachusetts, United States, in the center of the South Coast region, between the cities of New Bedford to the east and Fall River to the west. Formerly Southeastern Massachusetts University, it was merged into the University of Massachusetts system in 1991.

    The campus has an overall student body of 8,647 students (school year 2016-2017), including 6,999 undergraduates and 1,648 graduate/law students. As of the 2017 academic year, UMass Dartmouth records 399 full-time faculty on staff. For the fourth consecutive year UMass Dartmouth receives top 20 national rank from President’s Higher Education Community Service Honor Roll for its civic engagement.

    The university also includes the University of Massachusetts School of Law, as the trustees of the state’s university system voted during 2004 to purchase the nearby Southern New England School of Law (SNESL), a private institution that was accredited regionally but not by the American Bar Association (ABA).
    UMass School of Law at Dartmouth opened its doors in September 2010, accepting all current SNESL students with a C or better average as transfer students, and achieved (provisional) ABA accreditation in June 2012. The law school achieved full accreditation in December 2016.

    In 2011, UMass Dartmouth became the first university in the world to have a sustainability report that met the top level of the world’s most comprehensive, credible, and widely used standard (the GRI’s G3.1 standard). In 2013, UMass Dartmouth became the first university in the world whose annual sustainability report achieved an A+ application level according to the Global Reporting Initiative G3.1 standard (by having the sources of data used in its annual sustainability report verified by an independent third party).

     
  • richardmitnick 9:23 pm on March 19, 2018 Permalink | Reply
    Tags: , , , Black Holes, , , Gravastar model, ,   

    From Sky & Telescope: “Physicist Proposes Alternative to Black Holes” 

    SKY&Telescope bloc

    Sky & Telescope

    March 19, 2018
    Ben Skuse

    A physicist has incorporated a quantum mechanical idea with general relativity to arrive at a new alternative to black hole singularities.

    1
    An artist’s rendering of Cygnus X-1, an X-ray-emitting black hole that formed when a large star caved in. (We see its X-rays now as it feeds from its stellar companion.) But are black holes the inevitable next step after neutron stars? NASA / CXC / M.Weiss.

    What do you get when you cross two hypothetical alternatives to black holes? A self-consistent semiclassical relativistic star, according to Raúl Carballo-Rubio (International School for Advanced Studies, Trieste, Italy) whose recently published results in the February 6th Physical Review Letters describe a new mathematical model for the fate of massive stars.

    When a massive star comes to the end of its life, it goes supernova, leaving behind a dense core that — according to conventional thought — continues to collapse to form either a neutron star or black hole. To which fate a particular star is destined comes down to its mass. Neutron stars find a balance between the repulsive force of quantum mechanical degeneracy pressure and the attractive force of gravity, while more massive cores collapse into black holes, unable to fight the overwhelming pull of their own gravity.

    Repulsive Gravity

    Now, Carballo-Rubio adds an extra force into the mix: quantum fluctuations. Quantum mechanics has shown that virtual particles spontaneously pop into and out of existence — the effects can be measured best in a vacuum, but these fluctuations can happen anywhere in spacetime. These particles can be thought of as fluctuations of positive and negative energy that under normal conditions would cancel out. But the extreme gravity of compact objects breaks this balance, effectively generating negative energy. This negative energy creates a repulsive gravitational force.

    “The existence of quantum [fluctuations] due to gravitational fields has been known since the late 1970s,” explains Carballo-Rubio. But physicists didn’t know how to take this effect into account in collapsing stars.

    Carballo-Rubio derived equations that combine general relativity and quantum mechanics in a way that accounts for quantum fluctuations. Moreover, he found solutions that balance attractive and negative gravity for stellar masses that would otherwise have produced black holes. Dubbing them “semiclassical relativistic stars,” these compact objects do not fully collapse under their own weight to form an event horizon, and are therefore not black holes.

    Hybrid Star

    Interestingly, Carballo-Rubio’s semiclassical relativistic stars bear hallmarks of previously proposed black hole alternatives: gravastars and black stars.

    Gravastars and black stars also consist of ordinary matter and quantum fluctuations. But when these ideas were first conceived, equations incorporating quantum flluctuations were not yet known, so theorists Carballo-Rubio’s stars, on the other hand, emerge naturally from a consistent set of equations based on known physics.

    Gravastars and black stars are structured differently: In gravastar cores, large quantum fluctuations push ordinary matter outward to form an ultra-thin shell at the surface. Black stars, on the other hand, balance matter and the quantum fluctuations throughout their structure.

    Carballo-Rubio’s stars are like a hybrid of the two previous ideas. “On the one hand, both matter and the quantum [fluctuations] are present throughout the structure, as in the black star model,” he says. “On the other, the star displays two distinct elements, namely a core and an ultra-thin shell, as in the gravastar model.”

    2
    Artist’s drawing of a neutron star. Casey Reed / Penn State University.

    The Question of Stability

    Whether these hybrid stars exist in the real world is a matter of debate. Carballo-Rubio’s solutions do not incorporate time, so it isn’t clear if a such a star would remain stable or rapidly morph into something else . . . like a black hole.

    “Equilibrium solutions can be found for a pen standing on its tip,” remarks relativistic astrophysicist Luciano Rezzolla (Institute of Theoretical Physics, Germany). “Such a solution is obviously unstable to small perturbations.”

    However, if Carballo-Rubio can show that his semiclassical relativistic stars are indeed dynamically stable — which he will start work on next — the next generation of gravitational wave observatories should offer the level of precision necessary in the coming decades to distinguish unconventional compact bodies from black holes, potentially providing evidence to support the existence of this new type of star.

    See the full article here .

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    Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 2:55 pm on February 23, 2018 Permalink | Reply
    Tags: , , , Black Holes, , ,   

    From UCSC: ” Novel search strategy advances the hunt for primordial black holes” 

    UC Santa Cruz

    UC Santa Cruz

    February 21, 2018
    Tim Stephens
    stephens@ucsc.edu

    Some theories of the early universe predict density fluctuations that would have created small “primordial black holes,” some of which could be drifting through our galactic neighborhood today and might even be bright sources of gamma rays.

    Researchers analyzing data from the Fermi Gamma-ray Space Telescope for evidence of nearby primordial black holes have come up empty, but their negative findings still allow them to put an upper limit on the number of these tiny black holes that might be lurking in the vicinity of Earth.

    NASA/Fermi Gamma Ray Space Telescope


    NASA’s Fermi Gamma-ray Space Telescope is a powerful space observatory that opens a wide window on the universe. Primordial black holes are a potential source of gamma rays, the highest-energy form of light. (Illustration credit: NASA)

    “Understanding how many primordial black holes are around today can help us understand the early universe better,” said Christian Johnson, a graduate student in physics at UC Santa Cruz who developed an algorithm to search data from Fermi’s Large Area Telescope (LAT) for the signatures of primordial black holes. Johnson is a corresponding author of a paper on the findings that has been accepted for publication in The Astrophysical Journal.

    Low-mass black holes are expected to emit gamma rays due to Hawking radiation, a theoretical prediction from the work of physicist Stephen Hawking and others. Hawking showed that quantum effects can give rise to particle-antiparticle pairs near the event horizon of a black hole, allowing one of the particles to fall into the black hole and the other to escape. The result is that the black hole emits radiation and loses mass.

    A small black hole that isn’t absorbing enough from its environment to offset the losses from Hawking radiation will steadily lose mass and eventually evaporate entirely. The smaller it gets, the brighter it “burns,” emitting more and more Hawking radiation before exploding in a final cataclysm. Previous searches for primordial black holes using ground-based gamma-ray observatories have looked for these brief explosions, but Fermi should be able to detect the “burn phase” occurring over a period of several years.

    A limitation of the Fermi search was that it could only extend a relatively short distance from Earth (a small fraction of the distance to the nearest star). The advantage of looking nearby, however, is that primordial black holes could be distinguished from other sources of gamma rays by their movement on the sky.

    “It’s like looking at the sky at night and trying to decide if something is an airplane or a star,” Johnson explained. “If it’s an airplane, it will move, and if it’s a star it will stay put.”

    Any primordial black holes still around today would have started out much larger and have been gradually losing mass for billions of years. To detect one with Fermi, it would have to have reached the final burn phase during the roughly four-year observation period of the study. Over a period of a few years, it would go from undetectably dim to extremely bright, and would burn brightly for several years before exploding, Johnson said.

    “Even though we didn’t detect any, the non-detection sets a limit on the rate of explosions and gives us better constraints than previous research,” he said.

    In addition to Johnson, the other corresponding authors of the paper include Steven Ritz, professor of physics and director of the Santa Cruz Institute of Particle Physics at UCSC; and Stefan Funk and Dmitry Malyshev at the Erlangen Centre for Astroparticle Physics in Germany. Other members of the Fermi-LAT Collaboration also contributed to this work and are coauthors of the paper.

    See the full article here .

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    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    UC Santa Cruz campus
    The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

    UCSC is the home base for the Lick Observatory.

    Lick Observatory's Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building
    Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

    Search for extraterrestrial intelligence expands at Lick Observatory
    New instrument scans the sky for pulses of infrared light
    March 23, 2015
    By Hilary Lebow
    1
    The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

    Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

    “Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

    Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

    Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

    5
    UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

    Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

    “The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

    The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

    Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

    “We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

    Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

    “This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

    NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

    “Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

    NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

    The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

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    UCSC is the home base for the Lick Observatory.

     
  • richardmitnick 2:44 pm on February 21, 2018 Permalink | Reply
    Tags: , , , Black Holes, , IAC CanariCam on the Gran Telescopio Canarias at Roque de los Muchachos Observatory, MNRAS,   

    From RAS: “Magnetic field traces gas and dust swirling around supermassive black hole” 

    Royal Astronomical Society

    Royal Astronomical Society

    21 February 2018

    Media contacts

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7292 3979
    Mob: +44 (0)7802 877699
    rmassey@ras.ac.uk

    Dr Helen Klus
    Royal Astronomical Society
    Tel: +44 (0)20 7292 3976
    hklus@ras.ac.uk

    Science contact

    Professor Pat Roche
    University of Oxford
    pat.roche@physics.ox.ac.uk

    Astronomers reveal a new high resolution map of the magnetic field lines in gas and dust swirling around the supermassive black hole at the centre of our Galaxy, published in a new paper in Monthly Notices of the Royal Astronomical Society.

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

    The team, led by Professor Pat Roche of the University of Oxford, created the map, which is the first of its kind, using the CanariCam infrared camera attached to the Gran Telescopio Canarias sited on the island of La Palma.

    IAC CanariCam on the Gran Telescopio Canarias at Roque de los Muchachos Observatory island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    Black holes are objects with gravitational fields so strong that not even light can escape their grasp. The centre of almost every galaxy appears to host a black hole, and the one we live in, the Milky Way, is no exception. Stars move around the black hole at speeds of up to 30 million kilometres an hour, indicating that it has a mass of more than a million times our Sun.

    2
    The colour scale in the image shows the amount of infrared (heat) radiation coming from warm dust particles in the filaments and luminous stars within a light year of the Galactic centre. The position of the black hole is indicated by an asterisk. The lines trace the magnetic field directions and reveal the complex interactions between the stars and the dusty filaments, and the impact that they and the gravitational force has on them. Credit: E. Lopez-Rodriguez / NASA Ames / University of Texas at San Antonio.

    Visible light from sources in the centre of the Milky Way is blocked by clouds of gas and dust. Infrared light, as well as X-rays and radio waves, passes through this obscuring material, so astronomers use this to see the region more clearly. CanariCam combines infrared imaging with a polarising device, which preferentially filters light with the particular characteristics associated with magnetic fields.

    The new infrared map covers a region about 1 light year on each side of the supermassive black hole. The map shows the intensity of infrared light, and traces magnetic field lines within filaments of warm dust grains and hot gas, which appear as thin lines reminiscent of brush strokes in a painting.

    The filaments, several light years long, appear to meet close to the black hole (at a point below centre in the map), and may indicate where orbits of streams of gas and dust converge. One prominent feature links some of the brightest stars in the centre of the Galaxy. Despite the strong winds flowing from these stars, the filaments remain in place, bound by the magnetic field within them. Elsewhere the magnetic field is less clearly aligned with the filaments. Depending on how the material flows, some of it may eventually be captured and engulfed by the black hole.

    The new observations give astronomers more detailed information on the relationship between the bright stars and the dusty filaments. The origin of the magnetic field in this region is not understood, but it is likely that a smaller magnetic field is stretched out as the filaments are elongated by the gravitational influence of the black hole and stars in the galactic centre.

    Roche praises the new technique and the result: “Big telescopes like GTC, and instruments like CanariCam, deliver real results. We’re now able to watch material race around a black hole 25,000 light years away, and for the first time see magnetic fields there in detail.”

    The team are using CanariCam to probe magnetic fields in dusty regions in our galaxy. They hope to obtain further observations of the Galactic Centre to investigate the larger scale magnetic field and how it links to the clouds of gas and dust orbiting the black hole further out at distances of several light years.

    Science paper:
    The Magnetic Field in the central parsec of the Galaxy

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
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