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  • richardmitnick 12:02 pm on August 28, 2017 Permalink | Reply
    Tags: Accretion disks, , , Auger decay, , Black hole models contradicted by hands-on tests at Sandia’s Z machine, , , , 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
    nsinger@sandia.gov
    (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

    2
    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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    Sandia Campus
    Sandia National Laboratory

    Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.
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  • richardmitnick 1:20 pm on February 5, 2017 Permalink | Reply
    Tags: Accretion disks, , , , Maarten Schmidt, , quasi-stellar radio source 3C273,   

    From EarthSky: “Today in science: Quasar mystery solved” A Fascinating Look Back to February 5, 1963 

    1

    EarthSky

    February 5, 2017
    Deborah Byrd

    1
    Maarten Schmidt via CalTech

    February 5, 1963. On this date, Caltech astronomer Maarten Schmidt solved a puzzle about the quasi-stellar radio source 3C273 that changed the way we think about our universe.

    1
    X-ray image of 3C273 and its jet. Today, this quasar is known to lie at the center of a giant elliptical galaxy. Image via Chandra X-ray Observatory.

    This object appeared starlike, like a point of light, with a mysterious jet. But its spectrum – the range of wavelengths of its light – looked odd. Astronomers routinely use spectra to learn the composition of distant objects. But, in 1963, emission lines in the spectrum of 3C273 didn’t appear to match any known chemical elements. Schmidt had a sudden realization that 3C273 contained the very ordinary element hydrogen. He realized that the spectral lines of hydrogen appeared strange because they were highly shifted toward the red end of the spectrum. Such a large red shift could occur if 3C273 were very distant, about three billion light-years away.

    Dr. Schmidt told EarthSky that he recognized immediately the implications of his revelation. He said:

    “This realization came immediately: my wife still remembers that I was pacing up and down much of the evening”

    The implications were just this. To be so far away and still visible, 3C273 must be intrinsically very bright and very powerful. It’s now thought to shine with the light of two trillion stars like our sun. That’s hundreds of times the light of our entire Milky Way galaxy. Yet 3C273 appears to be less than a light-year across, in contrast to 100,000 light-years for our Milky Way.

    So 3C273 is not only distant. It is also exceedingly luminous, implying powerful energy-producing processes unknown in 1963. Schmidt announced his revelation about quasars in the journal Nature on March 16, 1963.

    Today, hundreds of thousands of quasars are known, and many are more distant and more powerful than 3C273. It’s no exaggeration to say they turned the science of astronomy on its ear. Why, for example, are these powerful quasars located so far away in space? Because light travels at a finite speed (186,000 miles per second), we are seeing distant objects in space in the distant past. In other words, quasars existed in early universe. They do not exist in our time. Why?

    In the 1960s, 3C273 and other quasars like it were strong evidence against the Fred Hoyle’s Steady State theory, which suggested that matter is continuously being created as the universe expands, leading to a universe that is the same everywhere. The quasars showed the universe is not the same everywhere and thus helped usher in Big Bang cosmology.

    2
    Timeline of the universe. A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of “inflation” produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light; it also forms a backlight for later developments of the universe.
    Date circa 2006
    Author NASA/WMAP Science Team

    ESA/Planck supercedes WMAP
    3
    21 March 2013
    ESA’s Planck satellite has delivered its first all-sky image of the Cosmic Microwave Background (CMB), bringing with it new challenges about our understanding of the origin and evolution of the cosmos. The image has provided the most precise picture of the early Universe so far.

    But Steady State theory had been losing ground, even before 1963. The biggest change caused by Maarten Schmidt’s revelation about the quasar 3C273 was in the way we think about our universe.

    In other words, the idea that 3C273 was extremely luminous, and yet occupied such a relatively small space, suggested powerful energies that astronomers had not contemplated before. 3C273 gave astronomers one of their first hints that we live in a universe of colossal explosive events – and extreme temperatures and luminosities – a place where mysterious black holes abound and play a major role.

    According to a March 2013 email from Caltech:

    In 1963, Schmidt’s discovery gave us an unprecedented look at how the universe behaved at a much younger period in its history – billions of years before the birth of the sun and its planets. Later, Schmidt, along with his colleague Donald Lynden-Bell, discovered that quasars are galaxies harboring supermassive black holes billions of light-years away – not stars in our own galaxy, as was once believed. His seminal work dramatically increased the scale of the observable universe and advanced our present view on the violent nature of the universe in which massive black holes play a dominant role.

    What are quasars? Astronomers today believe that a quasar is a compact region in the center of a galaxy in the early universe. The compact region is thought to surround a central supermassive black hole, much like the black hole thought to reside in the center of our own Milky Way galaxy and many (or most) other galaxies. The powerful luminosity of a quasar is thought to be the result of processes taking place in an accretion disk, or disk of material surrounding the black hole, as these supermassive black holes consume stars that pass too near.

    4
    ULAS J1120+0641, farthest quasar known as of 2011. The quasar appears as a faint red dot close to the center. Composite image created from the Sloan Digital Sky Survey and the UKIRT Infrared Deep Sky Survey, via Wikimedia Commons.

    SDSS Telescope at Apache Point Observatory, NM, USA
    SDSS Telescope at Apache Point Observatory, NM, USA

    UKIRT, located on Mauna Kea, Hawaii, USA as part of Mauna Kea Observatory
    UKIRT interior
    UKIRT, located on Mauna Kea, Hawaii, USA as part of Mauna Kea Observatory

    The Chinese-born U.S. astrophysicist Hong-Yee Chiu coined the name quasar in May 1964, in the publication Physics Today. He wrote:

    So far, the clumsily long name ‘quasi-stellar radio sources’ is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form ‘quasar’ will be used throughout this paper.

    Today, the farthest known quasar is ULAS J1120+0641. Its co-moving distance is 28.85 billion light-years.

    Bottom line: On February 5 1963, astronomer Maarten Schmidt’s flash of inspiration led to the understanding that quasi-stellar radio sources, or quasars, exist in the very distant universe. Quasars became the most distant, and most luminous, objects known. They changed the way we think about the universe.

    See the full article here .

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  • richardmitnick 11:18 am on December 22, 2016 Permalink | Reply
    Tags: A better way to simulate accretion of the supermassive black hole at the center of the Milky Way is developed by PPPL and Princeton scientists, Accretion disks, Kinetic approach, Pegasus computer code, ,   

    From PPPL: “A better way to simulate accretion of the supermassive black hole at the center of the Milky Way is developed by PPPL and Princeton scientists” 


    PPPL

    December 22, 2016
    John Greenwald

    1
    Image and inset of region surrounding Sagittarius A*. (Image: NASA/UMass/D.Wang et al. Inset: NASA/STScI)

    Scientists at Princeton University and the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have developed a rigorous new method for modeling the accretion disk that feeds the supermassive black hole at the center of our Milky Way galaxy.

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

    The paper, published online in December in the journal Physical Review Letters, provides a much-needed foundation for simulation of the extraordinary processes involved.

    Accretion disks are clouds of plasma that orbit and gradually swirl into massive bodies such as black holes — intense gravitational fields produced by stars that collapse to a tiny fraction of their original size. These collapsed stars are bounded by an “event horizon,” from which not even light can escape. As accretion disks flow toward event horizons, they power some of the brightest and most energetic sources of electromagnetic radiation in the universe.

    Four million times the mass of the sun

    The colossal black hole at the center of the Milky Way — called “Sagittarius A*” because it is found in the constellation Sagittarius — has a gravitational mass that is four million times greater than our own sun. Yet the accretion disk plasma that spirals into this mass is “radiatively inefficient,” meaning that it emits much less radiation than one would expect.

    “So the question is, why is this disk so quiescent?” asks Matthew Kunz, lead author of the paper, assistant professor of astrophysical sciences at Princeton University and a physicist at PPPL. Co-authors include James Stone, Princeton professor of astrophysical sciences, and Eliot Quataert, director of theoretical astrophysics at the University of California, Berkeley.

    To develop a method for finding the answer, the researchers considered the nature of the superhot Sagittarius A* accretion disk. Its plasma is so hot and dilute that it is collisionless, meaning that the trajectories of protons and electrons inside the plasma rarely intersect.

    This lack of collisionality distinguishes the Sagittarius A* accretion disk from brighter and more radiative disks that orbit other black holes. The brighter disks are collisional and can be modeled by formulas dating from the 1990s, which treat the plasma as an electrically conducting fluid. But “such models are inappropriate for accretion onto our supermassive black hole,” Kunz said, since they cannot describe the process that causes the collisionless Sagittarius A* disk to grow unstable and spiral down.

    Tracing collisionless particles

    To model the process for the Sagittarius A* disk, the paper replaces the formulas that treat the motion of collisional plasmas as a macroscopic fluid. Instead, the authors use a method that physicists call “kinetic” to systematically trace the paths of individual collisionless particles. This complex approach, conducted using the Pegasus computer code developed at Princeton by Kunz, Stone and Xuening Bai, now a lecturer at Harvard University, produced a set of equations better able to model behavior of the disk that orbits the supermassive black hole.

    This kinetic approach could help astrophysicists understand what causes the accretion disk region around the Sagittarius A* hole to radiate so little light. Results could also improve understanding of other key issues, such as how magnetized plasmas behave in extreme environments and how magnetic fields can be amplified.

    The goal of the new method, said Kunz, “will be to produce more predictive models of the emission from black-hole accretion at the galactic center for comparison with astrophysical observations.” Such observations come from instruments such as the Chandra X-ray observatory, an Earth-orbiting satellite that NASA launched in 1999, and the upcoming Event Horizon Telescope, an array of nine Earth-based radio telescopes located in countries around the world.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    Event Horizon Telescope Array

    Event Horizon Telescope map

    The locations of the radio dishes that will be part of the Event Horizon Telescope array. Image credit: Event Horizon Telescope sites, via University of Arizona at https://www.as.arizona.edu/event-horizon-telescope.

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

    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

    Future Array/Telescopes

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Research for this paper was funded by the National Science Foundation and grants from the Lyman Spitzer, Jr. Fellowship; a Simons Investigator Award from the Simons Foundation; and the David and Lucille Packard Foundation.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University. PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

     
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