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  • richardmitnick 4:41 pm on February 15, 2018 Permalink | Reply
    Tags: , , , Black Holes, , Guang Yang,   

    From Chandra: “The Billion-year Race Between Black Holes and Galaxies: Guang Yang” 

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    NASA Chandra Telescope

    NASA Chandra



    We welcome Guang Yang, a 4th-year Astronomy graduate student at Penn State, as a guest blogger. Guang led one of the two studies reported in our new press release about the evolution of supermassive black holes and galaxies. Before studying at Penn State, he obtained his astronomy B.S. degree at the University of Science and Technology of China.

    Supermassive black holes, with masses over million times that of our sun, sit in the centers of galaxies. The evolution of these black holes and their host galaxies in the past billions of years of cosmic history is still an unsolved mystery. A prevailing idea is that black hole growth is synchronized with host-galaxy growth, i.e., the ratio between black hole and galaxy growth is constant. “What a beautiful theory,” I told my advisor Prof. Niel Brandt, and colleagues Dr. Chien-Ting Chen and Dr. Fabio Vito. “But is it true?” I asked. “Has someone proved it?”

    We searched large amounts of literature but did not find dedicated works proving the idea, although it is widely quoted in published papers. “Then why not prove it with observations?” said my advisor. “It can be a great thesis topic for you.” I was so happy that my thesis topic was settled and I even dreamed about how our data might nicely support the theory.

    We painstakingly analyzed a large amount of data in the Chandra Deep Field-South & North and COSMOS surveys. We successfully tracked the black hole and galaxy growth in the distant universe with NASA’s Chandra, Hubble, Spitzer, and other observatories. The observations are so deep that we can study the evolution of black holes and their host galaxies 12 billion years in the past, when the Universe was less than 15% of its current age.

    “It is like watching a race between black holes and their host galaxies,” I joked with my colleagues, “I’m pretty sure nothing is missed, even though the race lasts for billions of years.” After obtaining the growth rates for black holes and galaxies, we eagerly compared them, thinking that we can finally prove the elegant theory of lockstep evolution.

    The results turned out to be surprisingly different from what we expected. Our data strongly disagree with the synchronization of black hole and galaxy growth. Instead, our work shows that black holes in big galaxies are growing much faster than small galaxies. It would be a little upsetting to kick out such a beautiful theory, but we must accept the results, since the Universe appears to work that way.

    By tracking the growth history of black holes and galaxies, we also predicted the accumulated black-hole mass in the current cosmic epoch, that is, the time we are living now. We found big galaxies have black holes with larger masses than we expected compared to small galaxies. If galaxy A is 10 times bigger than galaxy B, then its black hole is 100 times bigger than galaxy B’s black hole. The story appears to be quite different for big and small galaxies. In big galaxies, the black holes win the race against their hosts. But they lose in small galaxies.

    The progress represented by our discovery is quite dramatic. It teaches me that idealized theories might not be true, no matter how beautiful they are.

    see https://sciencesprings.wordpress.com/2018/02/15/from-chandra-supermassive-black-holes-are-outgrowing-their-galaxies/

    See the full article here .

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    NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

  • richardmitnick 4:27 pm on February 15, 2018 Permalink | Reply
    Tags: , , , Black Holes, , Mar Mezcua,   

    The Billion-year Race Between Black Holes and Galaxies: Mar Mezcua 

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    NASA Chandra

    Mar Mezcua

    Mar Mezcua is a postdoctoral researcher at the Institute of Space Sciences, in Barcelona (Spain), where she is from. She is a guest blogger today and the leading author of one of the two papers highlighted in our latest press release. She conducted this work last year with Prof. Julie Hlavacek Larrondo while at the University of Montreal (Canada).

    Supermassive black holes (SMBHs) started to fascinate me when I was 13 years old. These monsters reside at the center of massive galaxies and are the most energetic sources in the Universe. When they are actively accreting, the surrounding matter that feeds them (or that the black hole accretes) can radiate over a trillion times as much energy as the Sun, being able even to outshine the galaxy in which they reside. This feeding, or accreted, material emits X-ray radiation that we can detect with X-ray satellites such as Chandra, while the material that is ejected from the SMBH in the form of jets also often emit at radio wavelengths. (Yes, SMBHs do not only swallow but also emit outflows of energetic particles!) It is for all the above that I pursued a career in astrophysics in order to study these powerful behemoths in detail.

    My first close approach took place during my PhD, when I estimated the black holes (BH) masses of a sample of SMBHs whose radio jets had a peculiar morphology. To do this, I used the close relationships that had been recently found between the mass of SMBHs and some of their host galaxy properties, such as how much light was emitted by the central bulge or how quickly and where the stars in the bulge moved.

    The finding of such correlations suggested that SMBHs and their host galaxies grow in tandem — that there is a co-evolution — implying that SMBHs somehow regulate the growth of the galaxy in which they reside. As simple as it might sound, this was an astonishing discovery of the late 90’s. SMBHs typically have masses of between one million and one billion times that of the Sun and sizes similar to that of the Solar System, this is, nearly 10,000 times smaller than the galaxy that hosts them. That’s a huge difference in size! How is it then possible that such a ‘small’ central SMBH controls the whole budget of a galaxy? SMBHs were getting more and more exciting every time, so after my PhD I kept on studying them using all tools I had available: radio, optical, infrared and X-ray observations!

    I started to understand that the SMBH-galaxy synchronized growth can be explained by the effects of the outflows or jets ejected by the SMBH, which penetrate the host galaxy and can hamper (but can also trigger) the formation of stars and thus of stellar mass. The most extreme examples of such SMBH feedback are found in galaxy clusters, which host the brightest and most massive galaxies of the local Universe. So when Prof. Julie Hlavacek Larrondo offered me the possibility to move to Montreal to study SMBHs in galaxy clusters with her, I didn’t hesitate!

    The SMBHs of such brightest cluster galaxies emit radio jets that extend beyond the host galaxies. These jets enter the hot gas that permeates the space between the galaxies in the cluster, opening cavities in this X-ray emitting medium. The brightest cluster galaxies are elliptical galaxies that reside at the intersection of filaments of dark matter — ie material that makes up the bulk of matter in the Universe — in very dense environments, and are thus subject to conditions very different from those of isolated galaxies.

    This raised some pressing questions that intrigued us: Do the brightest cluster galaxies and their SMBHs then follow the same co-evolutionary galaxy/SMBH growth as other galaxies? Is the ratio between the growth rates of SMBHs and their host galaxies the same at the high-mass end, where brightest cluster galaxies are located, as it is at lower masses? In other words, is the BH/galaxy scaling relation the same? To probe this, we investigated the location of the brightest cluster galaxies on the “fundamental plane” of BH accretion, which is an empirical correlation supported by the theoretical expectation that BH accretion is a universal mechanism governing BHs of all masses. This fundamental plane correlates the mass of a BH with its nuclear X-ray luminosity and the radio luminosity of the core of its radio jet, and has been found to be valid both for stellar-mass BHs and SMBHs, thus unifying BHs across all mass scales. It is called a plane because that describes the shape of the relationship in three dimensions.

    Together with other collaborators from the University of Waterloo and Durham University, we took a sample of brightest cluster galaxies that had been observed by Chandra as well as by the major radio telescope arrays in the world. This gave us the SMBHs’ X-ray and radio luminosity, that is the amount of radiation produced. Assuming that the SMBHs followed the correlation between BH mass and bulge luminosity found for massive galaxies, we estimated their BH mass from the luminosity of the host galaxy and then located them on the fundamental plane of BH accretion using this BH mass, the nuclear X-ray luminosity and the core radio luminosity.

    And, surprise!! We found that the brightest cluster galaxies were on average offset from the fundamental plane by about a factor of 10, that is, the masses of their SMBHs were found to be higher than expected if the SMBHs followed the fundamental plane correlation! We investigated several possible explanations of this offset, and found that it did not seem to be caused by cooling of the radio jet. Nor does it appear to be a type of emission process assumed in the derivation of the fundamental plane correlation, among others.

    Black Holes in Chandra Deep Field South
    see https://sciencesprings.wordpress.com/2018/02/15/from-chandra-supermassive-black-holes-are-outgrowing-their-galaxies

    The offset of brightest cluster galaxies from the fundamental plane seemed to be due to the BH mass being underestimated, by the aforementioned factor of about 10, by the correlation between BH mass and bulge luminosity. In other words, the brightest cluster galaxies seem to be more overmassive than expected with respect to the SMBH-galaxy relations. This had been already suggested for a few brightest cluster galaxies for which accurate measurements of their SMBH masses revealed masses larger than predicted from the correlation between BH mass and stellar velocity dispersion, and implies that the BH-galaxy scaling relations do not hold for these extreme objects.

    That was a very exciting discovery for me, as just two years before I had found similar results for another type of elliptical galaxies (of smaller size and not located in galaxy clusters). So all together we seemed to be breaking down the sovereignty of BH-galaxy scaling relations!

    But wait, there’s still more! For the brightest cluster galaxies too, on average, follow the fundamental plane, a large fraction of them should have SMBHs with masses more than 10 billion times that of the Sun. This means they host “ultramassive” BHs. So now you might wonder, (as I did, you should!): how did such beasts form? One possibility is that they underwent a two-phase process in which the BH formed first very rapidly and the galaxy grew later at a slower pace, which defiantly challenges the current paradigm of a synchronized galaxy-BH growth. Alternatively, the SMBHs in the brightest cluster galaxies might be the descendants of the high-redshift, or very distant, seed BHs, invoked to explain the existence of SMBHs when the Universe was only about 0800 million years old. In this scenario, black holes would have grown via mergers following a standard hierarchical process.

    And guess what? As part of a different project in collaboration with the Harvard-Smithsonian Center for Astrophysics, I was (and still am!) precisely studying the presence of such seed BHs in dwarf galaxies also using Chandra data! Two independent projects, two different types of galaxies, but both related somehow to the first BHs formed in the early Universe! Astronomy doesn’t stop surprising me every day, which is what makes doing research so exciting!

    See the full article here .

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    NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.

  • richardmitnick 8:19 am on February 8, 2018 Permalink | Reply
    Tags: , Black Holes, , , ,   

    From STFC: “UK laser experiment mimics black hole environment” 


    7 February 2018

    The Gemini laser at CLF. (Credit: STFC)

    UK physicists have for the first time used an extremely powerful laser beam to slow down electrons travelling at near-light speeds – a quantum mechanical phenomenon thought to occur only around objects like black holes. By producing this effect in a lab, scientists hope to provide valuable insight into subatomic processes in the universe’s most extreme environments.

    Fast electrons, especially when they travel at near light speeds, are very difficult to stop. Often you require highly dense materials – such as lead – to stop them or slow them down. But now, scientists have shown that they can slow these superfast electrons using a very thin sheet of light; they squeeze trillions of light particles – photons – into a sheet that is a fraction of human hair in thickness.

    When light hits an object some of the light bounces back from the surface, often changing its colour (to even X-rays and gamma rays if the object is moving fast) – however, if the object is moving extremely fast and if the light is incredibly intense, strange things can happen.

    Electrons, for example, can be shaken so violently that they actually slow down because they radiate so much energy. Quantum physics is required to fully explain this phenomenon. Physicists call this process ‘radiation reaction’, which is thought to occur around objects such as black holes and quasars.

    Now, a team of researchers have demonstrated radiation reaction for the first time using the Gemini laser at the Science and Technology Facilities Council’s Central Laser Facility in Oxfordshire.

    Gemini scientist Dr Dan Symes said: “Experiments like these are extremely complicated to set up and very difficult to perform. Essentially, you need to focus a laser beam as big as an A4 size paper sheet down to a few microns and hit it with a micron-sized electron bullet that’s travelling very close to the speed of light.”

    Gemini Group Leader, Dr Rajeev Pattathil added: “You need two extremely well-synchronised high power laser beams for this: one to produce the high energy electron beam and another to shoot it. Gemini’s dual-beam capability makes it an ideal facility for these types of experiments. Gemini is one of the very few places in the world where such cutting-edge experiments can be performed.”

    The research team, led by Imperial College academic Dr Stuart Mangles, were able to observe this radiation reaction by colliding a laser beam that is one quadrillion times brighter than light at the surface of the Sun with a high-energy beam of electrons. All this energy had to be delivered in a very short duration – just 40 femtoseconds long, or 40 quadrillionths of a second.

    Senior author of the study [Physical Review X] Dr Mangles said: “We knew we had been successful in colliding the two beams when we detected very bright high energy gamma-ray radiation.

    “The real result then came when we compared this detection with the energy in the electron beam after the collision. We found that these successful collisions had a lower than expected electron energy, which is clear evidence of radiation reaction.”

    Study co-author Professor Alec Thomas, from Lancaster University and the University of Michigan, added: “One thing I always find so fascinating about this is that the electrons are stopped as effectively by this sheet of light, a fraction of a hair’s breadth thick, as by something like a millimetre of lead. That is extraordinary.”

    However more experiments at even higher intensity or with even higher energy electron beams will be needed to confirm if this is true. The team will be carrying out these experiments in the coming year.

    See the full article here .

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    Helping build a globally competitive, knowledge-based UK economy

    We are a world-leading multi-disciplinary science organisation, and our goal is to deliver economic, societal, scientific and international benefits to the UK and its people – and more broadly to the world. Our strength comes from our distinct but interrelated functions:

    Universities: we support university-based research, innovation and skills development in astronomy, particle physics, nuclear physics, and space science
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    We support an academic community of around 1,700 in particle physics, nuclear physics, and astronomy including space science, who work at more than 50 universities and research institutes in the UK, Europe, Japan and the United States, including a rolling cohort of more than 900 PhD students.

    STFC-funded universities produce physics postgraduates with outstanding high-end scientific, analytic and technical skills who on graduation enjoy almost full employment. Roughly half of our PhD students continue in research, sustaining national capability and creating the bedrock of the UK’s scientific excellence. The remainder – much valued for their numerical, problem solving and project management skills – choose equally important industrial, commercial or government careers.

    Our large-scale scientific facilities in the UK and Europe are used by more than 3,500 users each year, carrying out more than 2,000 experiments and generating around 900 publications. The facilities provide a range of research techniques using neutrons, muons, lasers and x-rays, and high performance computing and complex analysis of large data sets.

    They are used by scientists across a huge variety of science disciplines ranging from the physical and heritage sciences to medicine, biosciences, the environment, energy, and more. These facilities provide a massive productivity boost for UK science, as well as unique capabilities for UK industry.

    Our two Campuses are based around our Rutherford Appleton Laboratory at Harwell in Oxfordshire, and our Daresbury Laboratory in Cheshire – each of which offers a different cluster of technological expertise that underpins and ties together diverse research fields.

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    We think our science is awesome – and we know students, teachers and parents think so too. That’s why we run an extensive Public Engagement and science communication programme, ranging from loans to schools of Moon Rocks, funding support for academics to inspire more young people, embedding public engagement in our funded grant programme, and running a series of lectures, travelling exhibitions and visits to our sites across the year.

    Ninety per cent of physics undergraduates say that they were attracted to the course by our sciences, and applications for physics courses are up – despite an overall decline in university enrolment.

  • richardmitnick 7:48 am on January 22, 2018 Permalink | Reply
    Tags: , , , Black Holes, , New Study on Black Hole Magnetic Fields Has Thrown a Huge Surprise at Astronomers,   

    From Science Alert: “New Study on Black Hole Magnetic Fields Has Thrown a Huge Surprise at Astronomers” 


    Science Alert

    22 JAN 2018

    For the first time, scientists have studied the magnetic field of a black hole inside the Milky Way in multiple wavelengths – and found that it doesn’t conform to what we previously thought.

    X-ray echoes during V404 Cygni’s feeding event in 2015. (Andrew Beardmore & NASA/Swift)

    NASA Neil Gehrels Swift Observatory

    According to researchers at the University of Florida and the University of Texas at San Antonio, the black hole called V404 Cygni’s magnetic field is much weaker than expected – a discovery that means we may have to rework our current models for black hole jets.

    V404 Cygni, located around 7,800 light-years away in the constellation of Cygnus, is a binary microquasar system consisting of a black hole about 9 times the mass of the Sun, and its companion star, an early red giant slightly smaller than the Sun.

    In 2015, the system flared into life, and, over the course of about a week, periodically flashed with activity as the black hole devoured material from its companion star.

    At times, it was the brightest X-ray object in the sky; but it also showed, according to NASA-Goddard’s Eleonora Troja, “exceptional variation at all wavelengths” – offering a rare opportunity to study both V404 Cygni and black hole feeding activity.

    It was this period that the team, led by Yigit Dallilar at the University of Florida, studied.

    When black holes are active, they become surrounded by a brightly glowing accretion disc, lit by the gravitational and frictional forces that heat the material as it swirls towards the black hole.

    As they consume matter, black holes expel powerful jets of plasma at near light-speed from the coronae – regions of hot, swirling gas above and below the accretion disc.

    Previous research [Astronomy] has shown that these coronae and the jets are controlled by powerful magnetic fields – and the stronger the magnetic fields close to the black hole’s event horizon, the brighter its jets.

    This is because the magnetic fields are thought to act like a synchrotron, accelerating the particles that travel through it.

    Dallilar’s team studied V404 Cygni’s 2015 feeding event across optical, infrared, X-ray and radio wavelengths, and found rapid synchrotron cooling events that allowed them to obtain a precise measurement of the magnetic field.

    Their data revealed a much weaker magnetic field than predicted by current models.

    “These models typically talk about much larger magnetic fields at the base of the jet, which many assume to be equivalent to the corona,” Dallilar told Newsweek.

    “Our results indicate that these models might be oversimplified. Specifically, there may not be a single magnetic field value for each black hole.”

    Black holes themselves don’t have magnetic poles, and therefore don’t generate magnetic fields. This means that the accretion disc corona magnetic fields are somehow generated by the space around a black hole – a process that is not well understood at this point.

    This result doesn’t mean that previous findings showing strong magnetic fields are incorrect, but it does suggest that the dynamics may be a little more complicated than previously thought.

    The team’s research did find that synchrotron processes dominated the cooling events, but could not provide data on what caused the particles to accelerate in the first place. It is, as one has come to expect from black holes, a finding that answers one question and turns up a lot more in need of further research.

    “We need to understand black holes in general,” said researcher Chris Packham of the University of Texas at San Antonio.

    “If we go back to the very earliest point in our universe, just after the big bang, there seems to have always been a strong correlation between black holes and galaxies. It seems that the birth and evolution of black holes and galaxies, our cosmic island, are intimately linked.

    “Our results are surprising and one that we’re still trying to puzzle out.”

    The research has been published in the journal Science.

    See the full article here .

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  • richardmitnick 2:30 pm on January 19, 2018 Permalink | Reply
    Tags: , Black Holes, , U Texas San Antonio   

    From phys.org: “New research challenges existing models of black holes” 


    January 19, 2018
    Joanna Carver, University of Texas at San Antonio

    Credit: University of Texas at San Antonio

    Chris Packham, associate professor of physics and astronomy at The University of Texas at San Antonio (UTSA), has collaborated on a new study [Science] that expands the scientific community’s understanding of black holes in our galaxy and the magnetic fields that surround them.

    “Dr. Packham’s collaborative work on this study is a great example of the innovative research happening now in physics at UTSA. I’m excited to see what new research will result from these findings,” said George Perry, dean of the UTSA College of Sciences and Semmes Foundation Distinguished University Chair in Neurobiology.

    Packham and astronomers lead from the University of Florida observed the magnetic field of a black hole within our own galaxy from multiple wavelengths for the first time. The results, which were a collective effort among several researchers, are deeply enlightening about some of the most mysterious objects in space.

    A black hole is a place in space where gravity pulls so strongly that even light cannot escape its grasp. Black holes usually form when a massive star explodes and the remnant core collapses under the force of intense gravity. As an example, if a star around 3 times more massive than our own Sun became a black hole, it would be roughly the size of San Antonio. The black hole Packham and his collaborators featured in their study, which was recently published in Science, contains about 10 times the mass of our own sun and is known as V404 Cygni.

    “The Earth, like many planets and stars, has a magnetic field that sprouts out of the North Pole, circles the planet and goes back into the South Pole. It exists because the Earth has a hot, liquid iron rich core,” said Packham. “That flow creates electric currents that create a magnetic field. A black hole has a magnetic field as it was created from the remnant of a star after the explosion.”

    As matter is broken down around a black hole, jets of electrons are launched by the magnetic field from either pole of the black hole at almost the speed of light. Astronomers have long been flummoxed by these jets.

    These new and unique observations of the jets and estimates of magnetic field of V404 Cygni involved studying the body at several different wavelengths. These tests allowed the group to gain a much clearer understanding of the strength of its magnetic field. They discovered that magnetic fields are much weaker than previously understood, a puzzling finding that calls into question previous models of black hole components. The research shows a deep need for continued studies on some of the most mysterious entities in space.

    “We need to understand black holes in general,” Packham said. “If we go back to the very earliest point in our universe, just after the big bang, there seems to have always been a strong correlation between black holes and galaxies. It seems that the birth and evolution of black holes and galaxies, our cosmic island, are intimately linked. Our results are surprising and one that we’re still trying to puzzle out.”

    See the full article here .

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    About Phys.org in 100 Words

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

  • richardmitnick 10:32 am on January 10, 2018 Permalink | Reply
    Tags: Black Holes, Blue Waters supercomputer, , Relativistic jets’ behavior   

    From Northwestern University: “Black hole breakthrough: new insight into mysterious jets” 

    Northwestern U bloc
    Northwestern University

    January 09, 2018
    Kayla Stoner

    Supercomputer power enables advanced simulations of relativistic jets’ behavior.

    Through first-of-their-kind supercomputer simulations, researchers, including a Northwestern University professor, have gained new insight into one of the most mysterious phenomena in modern astronomy: the behavior of relativistic jets that shoot from black holes, extending outward across millions of light years.

    Advanced simulations created with one of the world’s most powerful supercomputers show the jets’ streams gradually change direction in the sky, or precess, as a result of space-time being dragged into the rotation of the black hole. This behavior aligns with Albert Einstein’s predictions about extreme gravity near rotating black holes, published in his famous theory of general relativity.

    This simulation produced using the Blue Waters supercomputer is the first simulation ever to demonstrate that relativistic jets follow along with the precession of the tilted accretion disk around the black hole. At close to a billion computational cells, it is the highest resolution simulation of an accreting black hole ever achieved.

    “Understanding how rotating black holes drag the space-time around them and how this process affects what we see through the telescopes remains a crucial, difficult-to-crack puzzle,” said Alexander Tchekhovskoy, assistant professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences. “Fortunately, the breakthroughs in code development and leaps in supercomputer architecture are bringing us ever closer to finding the answers.”

    The study, published in the Monthly Notices of the Royal Astronomical Society, is a collaboration between Tchekhovskoy, Matthew Liska and Casper Hesp. Liska and Hesp are the study’s lead authors and graduate students at The University of Amsterdam, Netherlands.

    Rapidly spinning black holes not only engulf matter but also emit energy in the form of relativistic jets. Similar to how water in a bathtub forms a whirlpool as it goes down a drain, the gas and magnetic fields that feed a supermassive black hole swirl to form a rotating disk — a tangled spaghetti of magnetic field lines mixed into a broth of hot gas. As the black hole consumes this astrophysical soup, it gobbles up the broth but leaves the magnetic spaghetti dangling out of its mouth. This makes the black hole into a kind of launching pad from which energy, in the form of relativistic jets, shoots from the web of twisted magnetic spaghetti.

    The jets emitted by black holes are easier to study than the black holes themselves because the jets are so large. This study enables astronomers to understand how quickly the jet direction is changing, which reveals information about the black hole spin as well as the orientation and size of the rotating disk and other difficult-to-measure properties of black hole accretion.

    Whereas nearly all previous simulations considered aligned disks, in reality, most galaxies’ central supermassive black holes are thought to harbor tilted disks — meaning the disk rotates around a separate axis than the black hole itself. This study confirms that if tilted, disks change direction relative to the black hole, precessing around like a spinning top. For the first time, the simulations showed that such tilted disks lead to precessing jets that periodically change their direction in the sky.

    An important reason precessing jets were not discovered earlier is that 3-D simulations of the region surrounding a rapidly spinning black hole require an enormous amount of computational power. To address this issue, the researchers constructed the first black hole simulation code accelerated by graphical processing units (GPUs). A National Science Foundation grant enabled them to carry out the simulations on Blue Waters, one of the largest supercomputers in the world, located at the University of Illinois.

    U Illinois Urbana-Champaign Blue Waters Cray Linux XE/XK hybrid machine supercomputer

    Comparing a low resolution simulation (left) to the high-resolution simulation produced using Blue Waters (right) show the effect of resolution on tilted accretion models. The high resolution model shows that precession and alignment slow down as a result of disk expansion due to magnetic turbulence.

    The confluence of the fast code, which efficiently uses a cutting-edge GPU architecture, and the Blue Waters supercomputer allowed the team to carry out simulations with the highest resolution ever achieved – up to a billion computational cells.

    “The high resolution allowed us, for the first time, to ensure that small-scale turbulent disk motions are accurately captured in our models,” Tchekhovskoy said. “To our surprise, these motions turned out to be so strong that they caused the disk to fatten up and the disk precession to stop. This suggests that precession can come about in bursts.”

    Because accretion onto black holes is a highly complex system akin to a hurricane, but located so far away we cannot discern many details, simulations offer a powerful way of making sense of telescope observations and understanding the behavior of black holes.

    The simulation results are important for further studies involving rotating black holes, which are currently being conducted all over the world. Through these efforts, astronomers are attempting to understand recently discovered phenomena such as the first detections of gravitational waves from neutron star collisions and the accompanying electromagnetic fireworks as well as regular stars being engulfed by supermassive black holes.

    The calculations also are being applied to interpreting the observations of the Event Horizon Telescope (EHT), which captured the first recordings of the supermassive black hole shadow in the center of the Milky Way.

    Additionally, the jets’ precession could explain fluctuations in the intensity of light coming from around black holes, called quasi-periodic oscillations (QPOs). Such oscillations can occur similarly to the way in which the rotating beam of a lighthouse increases in intensity as it passes by an observer. QPOs were first discovered near black holes (as X-rays) in 1985 by Michiel van der Klis (University of Amsterdam), who is a co-author of the new article.

    See the full article here .

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    South Campus

    On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

    Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

    In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
    Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

    Northwestern is recognized nationally and internationally for its educational programs.

  • richardmitnick 1:57 pm on January 3, 2018 Permalink | Reply
    Tags: Black Holes, , ,   

    From Ethan Siegel: “2018 Will Be The Year Humanity Directly ‘Sees’ Our First Black Hole” 

    Ethan Siegel
    Jan 3, 2018

    The black hole, as illustrated in the movie Interstellar, shows an event horizon fairly accurately for a very specific class of rotating black holes. Image credit: Interstellar / R. Hurt / Caltech.

    The Event Horizon Telescope has come online and taken its data. Now, we wait for the results.

    Black holes are some of the most incredible objects in the Universe. There are places where so much mass has gathered in such a tiny volume that the individual matter particles cannot remain as they normally are, and instead collapse down to a singularity. Surrounding this singularity is a sphere-like region known as the event horizon, from inside which nothing can escape, even if it moves at the Universe’s maximum speed: the speed of light. While we know three separate ways to form black holes, and have discovered evidence for thousands of them, we’ve never imaged one directly. Despite all that we’ve discovered, we’ve never seen a black hole’s event horizon, or even confirmed that they truly had one. Next year, that’s all about to change, as the first results from the Event Horizon Telescope will be revealed, answering one of the longest-standing questions in astrophysics.

    Event Horizon Telescope Array

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

    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array, Chile

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    Greenland Telescope

    The idea of a black hole is nothing new, as scientists have realized for centuries that as you gather more mass into a given volume, you have to move at faster and faster speeds to escape from the gravitational well that it creates. Since there’s a maximum speed that any signal can travel at — the speed of light — you’ll reach a point where anything from inside that region is trapped. The matter inside will try to support itself against gravitational collapse, but any force-carrying particles it attempts to emit get bent towards the central singularity; there is no way to exert an outward push. As a result, a singularity is inevitable, surrounded by an event horizon. Anything that falls into the event horizon? Also trapped; from inside the event horizon, all paths lead towards the central singularity.

    An illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets, may describe the black hole at the center of our galaxy in many regards. Image credit: Mark A. Garlick.

    Practically, there are three mechanisms that we know of for creating real, astrophysical black holes.

    1.When a massive enough star burns through its fuel and goes supernova, the central core can implode, converting a substantial fragment of the pre-supernova star into a black hole.
    2.When two neutron stars merge, if their combined post-merger mass is more than about 2.5-to-2.75 solar masses, it will result in the production of a black hole.
    3.And if either a massive star or a cloud of gas can undergo direct collapse, it, too, will produce a black hole, where 100% of the initial mass goes into the final black hole.

    Artwork illustrating a simple black circle, perhaps with a ring around it, is an oversimplified picture of what an event horizon looks like. Image credit: Victor de Schwanberg.

    Over time, black holes can continue to devour matter, growing in both mass and size commensurately. If you double the mass of your black hole, its radius doubles as well. If you increase it tenfold, the radius goes up by a factor of ten, also. This means that as you go up in mass — as your black hole grows — its event horizon gets larger and larger. Since nothing can escape from it, the event horizon should appear as a black “hole” in space, blocking the light from all objects behind it, compounded by the gravitational bending of light due to the predictions of General Relativity. All told, we expect the event horizon to appear, from our point of view, 250% as large as the mass predictions would imply.

    A black hole isn’t just a mass superimposed over an isolated background, but will exhibit gravitational effects that stretch, magnify and distort background light due to gravitational lensing. Image credit: Ute Kraus, Physics education group Kraus, Universität Hildesheim; Axel Mellinger (background).

    Taking all of this into account, we can look at all the known black holes, including their masses and how far away they are, and compute which one should appear the largest from Earth. The winner? Sagittarius A*, the black hole at the center of our galaxy. Its combined properties of being “only” 27,000 light years distant while still reaching a spectacularly large mass that’s 4,000,000 times that of the Sun makes it #1. Interestingly, the black hole that hits #2 is the central black hole of M87: the largest galaxy in the Virgo cluster. Although it’s over 6 billion solar masses, it lies some 50–60 million light years away. If you want to see an event horizon, our own galactic center is the place to look.

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

    Some of the possible profile signals of the black hole’s event horizon as simulations of the Event Horizon Telescope indicate. Image credit: High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA, V. Fish et al., arXiv:1309.3519.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    If you had a telescope the size of Earth, and nothing in between us and the black hole to block the light, you’d be able to see it, no problem. Some wavelengths are relatively transparent to the intervening galactic matter, so if you look at long-wavelength light, like radio waves, you could potentially see the event horizon itself. Now, we don’t have a telescope the size of Earth, but we do have an array of radio telescopes all across the globe, and the techniques of combining this data to produce a single image. The Event Horizon Telescope brings the best of our current technology together, and should enable us to see our very first black hole.

    Instead of a single telescope, 15-to-20 radio telescopes are arrayed across the globe, observing the same target simultaneously. With up to 12,000 kilometers separating the most distant telescopes, objects as small as 15 microarcseconds (μas) can be resolved: the size of a fly on the Moon. Given the mass and distance of Sagittarius A*, we expect that to appear more than twice as large as that figure: 37 μas. At radio frequencies, we should see lots of charged particles accelerated by the black hole, but there should be a “void” where the event horizon itself lies. If we can combine the data correctly, we should be able to construct a picture of a black hole for the very first time.

    Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole’s accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results. Image credit: GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799.

    The telescopes comprising the Event Horizon Telescope took their very first shot at observing Sagittarius A* simultaneously last year. The data has been brought together, and it’s presently being prepared and analyzed. If everything operates as designed, we’ll have our first image in 2018. Will it appear as General Relativity predicts? There are some incredible things to test:

    -whether the black hole has the right size as predicted by general relativity,
    -whether the event horizon is circular (as predicted), or oblate or prolate instead,
    -whether the radio emissions extend farther than we thought, or
    -whether there are any other deviations from the expected behavior.

    The orientation of the accretion disk as either face-on (left two panels) or edge-on (right two panels) can vastly alter how the black hole appears to us. Image credit: ‘Toward the event horizon — the supermassive black hole in the Galactic Center’, Class. Quantum Grav., Falcke & Markoff (2013).

    Whatever we do (or don’t) wind up discovering, we’re poised to make an incredible breakthrough simply by constructing our first-ever image of a black hole. No longer will we need to rely on simulations or artist’s conceptions; we’ll have our very first actual, data-based picture to work with. If it’s successful, it paves the way for even longer baseline studies; with an array of radio telescopes in space, we could extend our reach from a single black hole to many hundreds of them. If 2016 was the year of the gravitational wave and 2017 was the year of the neutron star merger, then 2018 is set up to be the year of the event horizon. For any fan of astrophysics, black holes, and General Relativity, we’re living in the golden age. What was once deemed “untestable” has suddenly become real.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 2:52 pm on November 18, 2017 Permalink | Reply
    Tags: , , , Black Holes, , Could Matter Escape The Event Horizon During A Black Hole Merger?,   

    From Ethan Siegel: ” Could Matter Escape The Event Horizon During A Black Hole Merger?” 

    Ethan Siegel

    Nov 18, 2017

    Nothing can escape from a black hole… but could another black hole pull something out?

    Even though black holes should have accretion disks, and matter falling in from them, it doesn’t appear to be possible to escape from inside the event horizon once you cross over. Could anything change that? Image credit: NASA / Dana Berry (Skyworks Digital).

    Once you fall into the event horizon of a black hole, you can never escape. There’s no speed you could travel at, not even the speed of light, that would enable you to get out. But in General Relativity, space gets curved by the presence of mass and energy, and merging black holes are one of the most extreme scenarios of all. Is there any way that you could fall into a black hole, cross the event horizon, and then escape as your black hole’s event horizon gets distorted from a massive merger? That’s the question of Chris Mitchell, who asks:

    If two black holes merge, is it possible for matter that was within the event horizon of one black hole to escape? Could it escape and migrate to the other (more massive black hole)? What about escape to outside of both horizons?

    It’s a crazy idea, to be certain. But is it crazy enough to work? Let’s find out.

    When a massive enough star ends its life, or two massive enough stellar remnants merge, a black hole can form, with an event horizon proportional to its mass and an accretion disk of infalling matter surrounding it. Image credit: NASA/ESA Hubble, ESO, M. Kornmesser.

    The way you form a black hole is typically from the collapse of a massive star’s core, either in the aftermath of a supernova explosion, a neutron star merger, or via direct collapse. As far as we know, every black hole is formed out of matter that was once a part of a star, and so in many ways black holes are the ultimate stellar remnant. Some black holes form in isolation; others form as part of a binary system or even one with multiple stars. Over time, black holes can not only inspiral and merge, but devour other matter that falls inside the event horizon.

    In a Schwarzschild black hole, falling in leads you to the singularity, and darkness. No matter which direction you travel in, how you accelerate, etc., a crossover into the event horizon means an inevitable encounter with a singularity. Image credit: (Illustration) ESO, NASA/ESA Hubble, M. Kornmesser.

    When anything crosses into a black hole’s event horizon from the outside, that matter is immediately doomed. Inevitably, in a matter of mere seconds, it will find itself encountering the singularity at the center of a black hole: a single point for a non-rotating black hole, and a ring for a rotating one. The black hole itself will have no memory of which particles fell in or what their quantum state was. Instead, all that will remain, information-wise, is what the total mass, charge, and angular momentum of the black hole now is.

    In the final pre-merger stages, the spacetime surrounding a black hole pair will be distorted, as matter continues to fall into both black holes from the surrounding environment. At no point does it appear that anything will have the opportunity to escape from the inside to the outside of an event horizon. Image credit: NASA/Ames Research Center/C. Henze.

    So you might envision a scenario, then, where matter falls into a black hole during the final pre-merger stages, when one black hole is about to combine with another. Since black holes are always expected to have accretion disks, and throughout interstellar space there’s material simply zipping through, you should have particles crossing the event horizon all the time. That part’s a no-brainer, and so it makes sense to consider a particle that’s just entered the event horizon prior to the final moments of a merger.

    Could it possibly escape? Could it “jump” from one black hole to the other? Let’s examine the situation from a spacetime perspective.

    Computer simulation of two merging black holes and the spacetime distortions that they cause. While gravitational waves are copiously emitted, matter itself isn’t expected to escape. Image credit: MPI for Gravitational Physics Werner Benger, cc by-sa 4.0.

    When two black holes merge, they do so only after a long period of inspiral, where energy is radiated away via gravitational waves. Leading up to the final pre-merger moments, energy is radiated away. But that doesn’t cause the event horizon of either black hole to shrink; rather, that energy comes from spacetime in the center-of-mass region getting more and more heavily deformed. It’s the same as if you stole energy away from the planet Mercury; it would orbit closer to the Sun, but no properties of Mercury or the Sun would need to change.

    However, when the final moments of the merger are upon us, the event horizons of the two black holes do get deformed by the gravitational presence of one another. Fortunately, numerical relativists [Physical Review D] have already worked out exactly how this merger affects the event horizons, and it’s spectacularly informative.

    Despite the fact that up to ~5% of the total pre-merger mass of the black holes can be radiated away in the form of gravitational waves, you’ll notice that the event horizons never shrink; they simply grow a connection, distort a little bit, and then increase in total volume. That last point is important: if I have two black holes of equal mass, their event horizons take up a certain amount of volume in space. If I merge them to create a single black hole of double the mass of the two originals, the amount of volume taken up by the event horizon is now four times the original volume of the combined black holes. The mass of a black hole is directly proportional to its radius, but volume is proportional to radius cubed.

    While we’ve discovered a great many black holes, note that the radius of each one’s event horizon is directly proportional to its mass. Double the mass, double the radius, but that means the area increases fourfold and the volume increases eightfold! Image credit: LIGO/Caltech/Sonoma State (Aurore Simonnet).

    As it turns out, even if you kept a particle as close to stationary inside a black hole as possible, and made it fall towards the singularity as slowly as possible, there’s no way for it to get out. The total volume of the combined event horizons during a black hole merger goes up, not down, and no matter what the trajectory of an event-horizon-crossing particle is, it’s forever destined to be swallowed by the combined singularity of both black holes together.

    In many collision scenarios in astrophysics, there are ejecta, where matter from inside an object escapes during a cataclysmic event. But in the case of merging black holes, everything from inside remains inside; most of what was outside gets sucked in; and only a little bit of what was outside could conceivably escape. Once you fall in, you’re doomed, and nothing you throw at that black hole — even another black hole — will change that!

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

  • richardmitnick 2:20 pm on October 8, 2017 Permalink | Reply
    Tags: , , , Black Holes, , , , , Perimeter Institute of Theoretical Physics, , ,   

    From Quanta: Women in STEM: “Mining Black Hole Collisions for New Physics” Asimina Arvanitaki 

    Quanta Magazine
    Quanta Magazine

    July 21, 2016
    Joshua Sokol

    The physicist Asimina Arvanitaki is thinking up ways to search gravitational wave data for evidence of dark matter particles orbiting black holes.

    Asimina Arvanitaki during a July visit to the CERN particle physics laboratory in Geneva, Switzerland.
    Samuel Rubio for Quanta Magazine

    When physicists announced in February that they had detected gravitational waves firsthand, the foundations of physics scarcely rattled.

    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

    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)

    The signal exactly matched the expectations physicists had arrived at after a century of tinkering with Einstein’s theory of general relativity. “There is a question: Can you do fundamental physics with it? Can you do things beyond the standard model with it?” said Savas Dimopoulos, a theoretical physicist at Stanford University. “And most people think the answer to that is no.”

    Asimina Arvanitaki is not one of those people. A theoretical physicist at Ontario’s Perimeter Institute of Theoretical Physics,

    Perimeter Institute in Waterloo, Canada

    Arvanitaki has been dreaming up ways to use black holes to explore nature’s fundamental particles and forces since 2010, when she published a paper with Dimopoulos, her mentor from graduate school, and others. Together, they sketched out a “string axiverse,” a pantheon of as yet undiscovered, weakly interacting particles. Axions such as these have long been a favored candidate to explain dark matter and other mysteries.

    In the intervening years, Arvanitaki and her colleagues have developed the idea through successive papers. But February’s announcement marked a turning point, where it all started to seem possible to test these ideas. Studying gravitational waves from the newfound population of merging black holes would allow physicists to search for those axions, since the axions would bind to black holes in what Arvanitaki describes as a “black hole atom.”

    “When it came up, we were like, ‘Oh my god, we’re going to do it now, we’re going to look for this,’” she said. “It’s a whole different ball game if you actually have data.”

    That’s Arvanitaki’s knack: matching what she calls “well-motivated,” field-hopping theoretical ideas with the precise experiment that could probe them. “By thinking away from what people are used to thinking about, you see that there is low-hanging fruit that lie in the interfaces,” she said. At the end of April, she was named the Stavros Niarchos Foundation’s Aristarchus Chair at the Perimeter Institute, the first woman to hold a research chair there.

    It’s a long way to come for someone raised in the small Grecian village of Koklas, where the graduating class at her high school — at which both of her parents taught — consisted of nine students. Quanta Magazine spoke with Arvanitaki about her plan to use black holes as particle detectors. An edited and condensed version of those discussions follows.

    QUANTA MAGZINE: When did you start to think that black holes might be good places to look for axions?

    ASIMINA ARVANITAKI: When we were writing the axiverse paper, Nemanja Kaloper, a physicist who is very good in general relativity, came and told us, “Hey, did you know there is this effect in general relativity called superradiance?” And we’re like, “No, this cannot be, I don’t think this happens. This cannot happen for a realistic system. You must be wrong.” And then he eventually convinced us that this could be possible, and then we spent like a year figuring out the dynamics.
    What is superradiance, and how does it work?

    An astrophysical black hole can rotate. There is a region around it called the “ergo region” where even light has to rotate. Imagine I take a piece of matter and throw it in a trajectory that goes through the ergo region. Now imagine you have some explosives in the matter, and it breaks apart into pieces. Part of it falls into the black hole and part escapes into infinity. The piece that is coming out has more total energy than the piece that went in the black hole.

    You can perform the same experiment by scattering radiation from a black hole. Take an electromagnetic wave pulse, scatter it from the black hole, and you see that the pulse you got back has a higher amplitude.

    So you can send a pulse of light near a black hole in such a way that it would take some energy and angular momentum from the black hole’s spin?

    This is old news, by the way, this is very old news. In ’72 Press and Teukolsky wrote a Nature paper that suggested the following cute thing. Let’s imagine you performed the same experiment as the light, but now imagine that you have the black hole surrounded by a giant mirror. What will happen in that case is the light will bounce on the mirror many times, the amplitude [of the light] grows exponentially, and the mirror eventually explodes due to radiation pressure. They called it the black hole bomb.

    The property that allows light to do this is that light is made of photons, and photons are bosons — particles that can sit in the same space at the same time with the same wave function. Now imagine that you have another boson that has a mass. It can [orbit] the black hole. The particle’s mass acts like a mirror, because it confines the particle in the vicinity of the black hole.

    In this way, axions might get stuck around a black hole?

    This process requires that the size of the particle is comparable to the black hole size. Turns out that [axion] mass can be anywhere from Hubble scale — with a quantum wavelength as big as the universe — or you could have a particle that’s tiny in size.

    So if they exist, axions can bind to black holes with a similar size and mass. What’s next?

    What happens is the number of particles in this bound orbit starts growing exponentially. At the same time the black hole spins down. If you solve for the wave functions of the bound orbits, what you find is that they look like hydrogen wave functions. Instead of electromagnetism binding your atom, what’s binding it is gravity. There are three quantum numbers you can describe, just the same. You can use the exact terminology that you can use in the hydrogen atom.

    How could we check to see if any of the black holes LIGO finds have axion clouds orbiting around black hole nuclei?

    This is a process that extracts energy and angular momentum from the black hole. If you were to measure spin versus mass of black holes, you should see that in a certain mass range for black holes you see no quickly rotating black holes.

    This is where Advanced LIGO comes in. You saw the event they saw. [Their measurements] allowed them to measure the masses of the merging objects, the mass of the final object, the spin of the final object, and to have some information about the spins of the initial objects.

    If I were to take the spins of the black holes before they merged, they could have been affected by superradiance. Now imagine a graph of black hole spin versus mass. Advanced LIGO could maybe get, if the things that we hear are correct, a thousand events per year. Now you have a thousand data points on this plot. So you may trace out the region that is affected by this particle just by those measurements.

    That would be supercool.

    That’s of course indirect. So the other cool thing is that it turns out there are signatures that have to do with the cloud of particles themselves. And essentially what they do is turn the black hole into a gravitational wave laser.

    Awesome. OK, what does that mean?

    Samuel Rubio for Quanta Magazine

    Yeah, what that means is important. Just like you have transitions of electrons in an excited atom, you can have transitions of particles in the gravitational wave atom. The rate of emission of gravitational waves from these transitions is enhanced by the 1080 particles that you have. It would look like a very monochromatic line. It wouldn’t look like a transient. Imagine something now that emits a signal at a very fixed frequency.

    Where could LIGO expect to see signals like this?

    In Advanced LIGO, you actually see the birth of a black hole. You know when and where a black hole was born with a certain mass and a certain spin. So if you know the particle masses that you’re looking for, you can predict when the black hole will start growing the [axion] cloud around it. It could be that you see a merger in that day, and one or 10 years down the line, they go back to the same position and they see this laser turning on, they see this monochromatic line coming out from the cloud.

    You can also do a blind search. Because you have black holes that are roaming the universe by themselves, and they could still have some leftover cloud around them, you can do a blind search for monochromatic gravitational waves.

    Were you surprised to find out that axions and black holes could combine to produce such a dramatic effect?

    Oh my god yes. What are you talking about? We had panic attacks. You know how many panic attacks we had saying that this effect, no, this cannot be true, this is too good to be true? So yes, it was a surprise.

    The experiments you suggest draw from a lot of different theoretical ideas — like how we could look for high-frequency gravitational waves with tabletop sensors, or test whether dark matter oscillates using atomic clocks. When you’re thinking about making risky bets on physics beyond the standard model, what sorts of theories seem worth the effort?

    What is well motivated? Things that are not: “What if you had this?” People imagine: “What if dark matter was this thing? What if dark matter was the other thing?” For example, supersymmetry makes predictions about what types of dark matter should be there. String theory makes predictions about what types of particles you should have. There is always an underlying reason why these particles are there; it’s not just the endless theoretical possibilities that we have.

    And axions fit that definition?

    This is a particle that was proposed 30 years ago to explain the smallness of the observed electric dipole moment of the neutron. There are several experiments around the world looking for it already, at different wavelengths. So this particle, we’ve been looking for it for 30 years. This can be the dark matter. That particle solves an outstanding problem of the standard model, so that makes it a good particle to look for.

    Now, whether or not the particle is there I cannot answer for nature. Nature will have to answer.

    See the full article here .

    Please help promote STEM in your local schools.

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

  • richardmitnick 12:02 pm on August 28, 2017 Permalink | Reply
    Tags: , , , Auger decay, , Black hole models contradicted by hands-on tests at Sandia’s Z machine, Black Holes, , , Resonant Auger Destruction,   

    From Sandia Lab: “Black hole models contradicted by hands-on tests at Sandia’s Z machine” 

    Sandia Lab

    August 28, 2017
    Neal Singer
    (505) 845-7078

    A long-standing but unproven assumption about the X-ray spectra of black holes in space has been contradicted by hands-on experiments performed at Sandia National Laboratories’ Z machine.

    Sandia Z machine

    Z, the most energetic laboratory X-ray source on Earth, can duplicate the X-rays surrounding black holes that otherwise can be watched only from a great distance and then theorized about.

    “Of course, emission directly from black holes cannot be observed,” said Sandia researcher and lead author Guillaume Loisel, lead author for a paper on the experimental results, published in August in Physical Review Letters. “We see emission from surrounding matter just before it is consumed by the black hole. This surrounding matter is forced into the shape of a disk, called an accretion disk.”

    The results suggest revisions are needed to models previously used to interpret emissions from matter just before it is consumed by black holes, and also the related rate of growth of mass within the black holes. A black hole is a region of outer space from which no material and no radiation (that is, X-rays, visible light, and so on) can escape because the gravitational field of the black hole is so intense.

    “Our research suggests it will be necessary to rework many scientific papers published over the last 20 years,” Loisel said. “Our results challenge models used to infer how fast black holes swallow matter from their companion star. We are optimistic that astrophysicists will implement whatever changes are found to be needed.”

    Most researchers agree a great way to learn about black holes is to use satellite-based instruments to collect X-ray spectra, said Sandia co-author Jim Bailey. “The catch is that the plasmas that emit the X-rays are exotic, and models used to interpret their spectra have never been tested in the laboratory till now,” he said.

    NASA astrophysicist Tim Kallman, one of the co-authors, said, “The Sandia experiment is exciting because it’s the closest anyone has ever come to creating an environment that’s a re-creation of what’s going on near a black hole.”

    Theory leaves reality behind

    The divergence between theory and reality began 20 years ago, when physicists declared that certain ionization stages of iron (or ions) were present in a black hole’s accretion disk — the matter surrounding a black hole — even when no spectral lines indicated their existence.

    The complicated theoretical explanation was that under a black hole’s immense gravity and intense radiation, highly energized iron electrons did not drop back to lower energy states by emitting photons — the common quantum explanation of why energized materials emit light. Instead, the electrons were liberated from their atoms and slunk off as lone wolves in relative darkness. The general process is known as Auger decay, after the French physicist who discovered it in the early 20th century. The absence of photons in the black-hole case is termed Auger destruction, or more formally, the Resonant Auger Destruction assumption.

    However, Z researchers, by duplicating X-ray energies surrounding black holes and applying them to a dime-size film of silicon at the proper densities, showed that if no photons appear, then the generating element simply isn’t there. Silicon is an abundant element in the universe and experiences the Auger effect more frequently than iron. Therefore, if Resonant Auger Destruction happens in iron then it should happen in silicon too.

    “If Resonant Auger Destruction is a factor, it should have happened in our experiment because we had the same conditions, the same column density, the same temperature,” said Loisel. “Our results show that if the photons aren’t there, the ions must be not there either.”

    That deceptively simple finding, after five years of experiments, calls into question the many astrophysical papers based on the Resonant Auger Destruction assumption.

    The Z experiment mimicked the conditions found in accretion disks surrounding black holes, which have densities many orders of magnitude lower than Earth’s atmosphere.

    “Even though black holes are extremely compact objects, their accretion disks ­— the large plasmas in space that surround them — are relatively diffuse,” said Loisel. “On Z, we expanded silicon 50,000 times. It’s very low density, five orders of magnitude lower than solid silicon.”

    The spectra’s tale

    This is an artist’s depiction of the black hole named Cygnus X-1, formed when the large blue star beside it collapsed into the smaller, extremely dense matter. (Image courtesy of NASA)

    The reason accurate theories of a black hole’s size and properties are difficult to come by is the lack of first-hand observations. Black holes were mentioned in Albert Einstein’s general relativity theory a century ago but at first were considered a purely mathematical concept. Later, astronomers observed the altered movements of stars on gravitational tethers as they circled their black hole, or most recently, gravity-wave signals, also predicted by Einstein, from the collisions of those black holes. But most of these remarkable entities are relatively small — about 1/10 the distance from the Earth to the Sun — and many thousands of light years away. Their relatively tiny sizes at immense distances make it impossible to image them with the best of NASA’s billion-dollar telescopes.

    What’s observable are the spectra released by elements in the black hole’s accretion disk, which then feeds material into the black hole. “There’s lots of information in spectra. They can have many shapes,” said NASA’s Kallman. “Incandescent light bulb spectra are boring, they have peaks in the yellow part of their spectra. The black holes are more interesting, with bumps and wiggles in different parts of the spectra. If you can interpret those bumps and wiggles, you know how much gas, how hot, how ionized and to what extent, and how many different elements are present in the accretion disk.”

    Said Loisel: “If we could go to the black hole and take a scoop of the accretion disk and analyze it in the lab, that would be the most useful way to know what the accretion disk is made of. But since we cannot do that, we try to provide tested data for astrophysical models.”

    While Loisel is ready to say R.I.P. to the Resonant Auger Destruction assumption, he still is aware the implications of higher black hole mass consumption, in this case of the absent iron, is only one of several possibilities.

    “Another implication could be that lines from the highly charged iron ions are present, but the lines have been misidentified so far. This is because black holes shift spectral lines tremendously due to the fact that photons have a hard time escaping the intense gravitation field,” he said.

    There are now models being constructed elsewhere for accretion-powered objects that don’t employ the Resonant Auger Destruction approximation. “These models are necessarily complicated, and therefore it is even more important to test their assumptions with laboratory experiments,” Loisel said.

    The work is supported by the U.S. Department of Energy and the National Nuclear Security Administration.

    See the full article here .

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