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  • richardmitnick 8:37 am on October 4, 2018 Permalink | Reply
    Tags: Black Hole Mergers, Blue Waters supercomputer at the University of Illinois at Urbana-Champaign, , , ,   

    From NASA Goddard Space Flight Center via Manu Garcia of IAC: “New Simulation Sheds Light on Spiraling Supermassive Black Holes” 


    From Manu Garcia, a friend from IAC.

    The universe around us.
    Astronomy, everything you wanted to know about our local universe and never dared to ask.

    NASA Goddard Banner
    From NASA Goddard Space Flight Center

    Oct. 2, 2018
    Jeanette Kazmierczak
    jeanette.a.kazmierczak@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    1
    This animation rotates 360 degrees around a frozen version of the simulation in the plane of the disk. Credit: NASA’s Goddard Space Flight Center

    A new model is bringing scientists a step closer to understanding the kinds of light signals produced when two supermassive black holes, which are millions to billions of times the mass of the Sun, spiral toward a collision. For the first time, a new computer simulation that fully incorporates the physical effects of Einstein’s general theory of relativity shows that gas in such systems will glow predominantly in ultraviolet and X-ray light.

    Just about every galaxy the size of our own Milky Way or larger contains a monster black hole at its center. Observations show galaxy mergers occur frequently in the universe, but so far no one has seen a merger of these giant black holes.

    “We know galaxies with central supermassive black holes combine all the time in the universe, yet we only see a small fraction of galaxies with two of them near their centers,” said Scott Noble, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The pairs we do see aren’t emitting strong gravitational-wave signals because they’re too far away from each other. Our goal is to identify — with light alone — even closer pairs from which gravitational-wave signals may be detected in the future.”

    A paper describing the team’s analysis of the new simulation was published Tuesday, Oct. 2, in The Astrophysical Journal.


    Gas glows brightly in this computer simulation of supermassive black holes only 40 orbits from merging. Models like this may eventually help scientists pinpoint real examples of these powerful binary systems. Credits: NASA’s Goddard Space Flight Center

    Scientists have detected merging stellar-mass black holes — which range from around three to several dozen solar masses — using the National Science Foundation’s Laser Interferometer Gravitational-Wave Observatory (LIGO).

    Gravitational waves are space-time ripples traveling at the speed of light. They are created when massive orbiting objects like black holes and neutron stars spiral together and merge.

    Black holes heading toward a merger. Precise laser interferometry can detect the ripples in space-time generated when two black holes collide. LIGO-Caltech-MIT-Sonoma State Aurore Simonn

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Supermassive mergers will be much more difficult to find than their stellar-mass cousins. One reason ground-based observatories can’t detect gravitational waves from these events is because Earth itself is too noisy, shaking from seismic vibrations and gravitational changes from atmospheric disturbances. The detectors must be in space, like the Laser Interferometer Space Antenna (LISA) led by ESA (the European Space Agency) and planned for launch in the 2030s.


    ESA/NASA eLISA space based, the future of gravitational wave research

    Observatories monitoring sets of rapidly spinning, superdense stars called pulsars may detect gravitational waves from monster mergers. Like lighthouses, pulsars emit regularly timed beams of light that flash in and out of view as they rotate. Gravitational waves could cause slight changes in the timing of those flashes, but so far studies haven’t yielded any detections.

    But supermassive binaries nearing collision may have one thing stellar-mass binaries lack — a gas-rich environment. Scientists suspect the supernova explosion that creates a stellar black hole also blows away most of the surrounding gas. The black hole consumes what little remains so quickly there isn’t much left to glow when the merger happens.

    Supermassive binaries, on the other hand, result from galaxy mergers. Each supersized black hole brings along an entourage of gas and dust clouds, stars and planets. Scientists think a galaxy collision propels much of this material toward the central black holes, which consume it on a time scale similar to that needed for the binary to merge. As the black holes near, magnetic and gravitational forces heat the remaining gas, producing light astronomers should be able to see.

    “It’s very important to proceed on two tracks,” said co-author Manuela Campanelli, director of the Center for Computational Relativity and Gravitation at the Rochester Institute of Technology in New York, who initiated this project nine years ago. “Modeling these events requires sophisticated computational tools that include all the physical effects produced by two supermassive black holes orbiting each other at a fraction of the speed of light. Knowing what light signals to expect from these events will help modern observations identify them. Modeling and observations will then feed into each other, helping us better understand what is happening at the hearts of most galaxies.”

    The new simulation shows three orbits of a pair of supermassive black holes only 40 orbits from merging. The models reveal the light emitted at this stage of the process may be dominated by UV light with some high-energy X-rays, similar to what’s seen in any galaxy with a well-fed supermassive black hole.

    Three regions of light-emitting gas glow as the black holes merge, all connected by streams of hot gas: a large ring encircling the entire system, called the circumbinary disk, and two smaller ones around each black hole, called mini disks. All these objects emit predominantly UV light. When gas flows into a mini disk at a high rate, the disk’s UV light interacts with each black hole’s corona, a region of high-energy subatomic particles above and below the disk. This interaction produces X-rays. When the accretion rate is lower, UV light dims relative to the X-rays.

    Based on the simulation, the researchers expect X-rays emitted by a near-merger will be brighter and more variable than X-rays seen from single supermassive black holes. The pace of the changes links to both the orbital speed of gas located at the inner edge of the circumbinary disk as well as that of the merging black holes.


    This 360-degree video places the viewer in the middle of two circling supermassive black holes around 18.6 million miles (30 million kilometers) apart with an orbital period of 46 minutes. The simulation shows how the black holes distort the starry background and capture light, producing black hole silhouettes. A distinctive feature called a photon ring outlines the black holes. The entire system would have around 1 million times the Sun’s mass. Credits: NASA’s Goddard Space Flight Center; background, ESA/Gaia/DPAC

    “The way both black holes deflect light gives rise to complex lensing effects, as seen in the movie when one black hole passes in front of the other,” said Stéphane d’Ascoli, a doctoral student at École Normale Supérieure in Paris and lead author of the paper. “Some exotic features came as a surprise, such as the eyebrow-shaped shadows one black hole occasionally creates near the horizon of the other.”

    The simulation ran on the National Center for Supercomputing Applications’ Blue Waters supercomputer at the University of Illinois at Urbana-Champaign.

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

    Modeling three orbits of the system took 46 days on 9,600 computing cores. Campanelli said the collaboration was recently awarded additional time on Blue Waters to continue developing their models.

    The original simulation estimated gas temperatures. The team plans to refine their code to model how changing parameters of the system, like temperature, distance, total mass and accretion rate, will affect the emitted light. They’re interested in seeing what happens to gas traveling between the two black holes as well as modeling longer time spans.

    “We need to find signals in the light from supermassive black hole binaries distinctive enough that astronomers can find these rare systems among the throng of bright single supermassive black holes,” said co-author Julian Krolik, an astrophysicist at Johns Hopkins University in Baltimore. “If we can do that, we might be able to discover merging supermassive black holes before they’re seen by a space-based gravitational-wave observatory.”

    See the full article here.


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


    NASA/Goddard Campus

     
  • richardmitnick 3:32 pm on June 15, 2017 Permalink | Reply
    Tags: , , , Black Hole Mergers, , , ,   

    From Ethan Siegel: “Newest LIGO signal raises a huge question: do merging black holes emit light?” 

    Ethan Siegel
    June 15, 2017

    1
    There are many cases in the Universe, such as imploding stars or neutron star collisions, that are strongly suspected of creating high-energy bursts of electromagnetic energy. Black hole mergers aren’t supposed to be one of them, but the observational data may yet surprise us. Image credit: NASA / Skyworks Digital.

    Gravitational waves and electromagnetic ones don’t need to go together. But physics says it’s possible; what do the observations say?

    “The black holes collide in complete darkness. None of the energy exploding from the collision comes out as light. No telescope will ever see the event.”
    -Janna Levin

    Billions of years ago, two black holes much more massive than the Sun — 31 and 19 solar masses each — merged together in a distant galaxy far across the Universe. On January 4th of this year, those gravitational waves, traveling through the Universe at the speed of light, finally reached Earth, where they compressed and stretched our planet by the width of no more than a few atoms. Yet that was enough for the twin LIGO detectors in Washington and Louisiana to pick up the signal and reconstruct exactly what happened. For the third time ever, we had directly detected gravitational waves. Meanwhile, telescopes and observatories all over the world, including in orbit around Earth, were looking for an entirely different signal: for some type of light, or electromagnetic radiation, that these merging black holes might have produced.

    2
    Illustration of two black holes merging, of comparable mass to what LIGO has seen. The expectation is that there ought to be very little in the way of an electromagnetic signal emitted from such a merger, but the presence of strongly heated matter surrounding these objects could change that. Image credit:Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project (http://www.black-holes.org).

    According to our best models of physics, merging black holes aren’t supposed to emit any light at all. A massive singularity surrounded by an event horizon might emit gravitational waves, due to the changing curvature of space time as it orbits an inspirals with another giant mass, in line with General Relativity’s predictions. Because that gravitational energy, emitted as radiation, needs to come from somewhere, the final black hole post-merger is about two solar masses lighter than the sum of the originals that created it. This is completely in line with the other two mergers LIGO observed: where around 5% of the original masses were converted into pure energy, in the form of gravitational radiation.


    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

    3
    The masses of known binary black hole systems, including the three verified mergers and one merger candidate coming from LIGO. Image credit: LIGO/Caltech/Sonoma State (Aurore Simonnet).

    But if there’s anything outside of those black holes, such as an accretion disk, a firewall, a hard shell, a diffuse cloud, or any other possibility, the acceleration and heating of that material could conceivably create electromagnetic radiation traveling right alongside those gravitational waves. In the aftermath of the first LIGO detection, the Fermi Gamma-ray Burst Monitor made headlines as they claimed to detect a high energy burst of radiation coincident within a second of the gravitational wave signal.

    NASA/Fermi Telescope


    NASA/Fermi LAT

    Unfortunately, ESA’s Integral satellite not only failed to confirm Fermi’s results, but scientists working there uncovered a flaw in Fermi’s analysis of their data, completely discrediting their results.

    ESA/Integral

    4
    Artist’s impression of two merging black holes, with accretion disks. The density and energy of the matter here should be insufficient to create gamma ray or X-ray bursts, but you never know what nature holds. Image credit: NASA / Dana Berry (Skyworks Digital).

    The second merger held no such hints of electromagnetic signals, but that was less surprising: the black holes were of significantly lower mass, so any signal arising from them would be expected to be correspondingly lower in magnitude. But the third merger was large in mass again, more comparable to the first than the second. While Fermi has made no announcement, and Integral again reports a non-detection, there are two pieces of evidence that suggest there may have been an electromagnetic counterpart after all. The AGILE satellite from the Italian Space Agency detected a weak, short-lived event that occurred just half a second before the LIGO merger, while X-ray, radio and optical observations combined to identify a strange afterglow less than 24 hours after the merger.

    Italian Space Agency AGILE Spacecraft

    5
    Our galaxy’s supermassive black hole has witnessed some incredibly bright flares, but none as bright or long-lasting as XJ1500+0134. These transient events and afterglows do occur for quite some time, but if they’re associated with a gravitational merger, you’d expect the arrival time of the electromagnetic and gravitational wave signals to be concurrent. Image credit: NASA/CXC/Stanford/I. Zhuravleva et al.

    If either of these were connected to the black hole merger, it would be absolutely revolutionary. There is so little we presently know about black holes in general, much less merging black holes. We’ve never directly imaged one before, although the Event Horizon Telescope hopes to grab the first later this year.

    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

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

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    We’ve only just this year determined that black holes don’t have hard shells encircling the event horizon, and even that evidence is only statistical. So when it comes to the possibility that black holes might have an electromagnetic counterpart, it’s important to keep an open mind, to look, and to go wherever the data takes us.

    6
    Distant, massive quasars show ultramassive black holes in their cores, and their electromagnetic counterparts are easy to detect. But it remains to be seen whether merging black holes, particularly of these lower-mass (under 100 Suns) mergers, emit anything detectable. Image credit: J. Wise/Georgia Institute of Technology and J. Regan/Dublin City University.

    Unfortunately, neither one of these observations provide the necessary data to take us to a place where we’d conclude that merging black holes really do have a light-emitting counterpart. It’s very difficult to get compelling evidence in the first place, since even the twin LIGO detectors, operating with their incredible precision, can’t pinpoint the location of a gravitational wave signal to better accuracy than a constellation or three. Since gravitational waves and electromagnetic waves both travel at the speed of light, it’s extraordinarily unlikely that there would be nearly a 24 hour delay between a gravitational wave signal and an electromagnetic signal; in addition, that transient event appears to occur at a distance far too great to be associated with the gravitational wave event.

    7
    The observational field-of-view of the AGILE observatory during the moment of the LIGO observations (in color), with the possible location of the gravitational wave source shown in the magenta outlines.

    But the AGILE observations may potentially provide a hint that something interesting is going on. At the moment that the gravitational wave event occurred, AGILE was pointed at a region of space that contains 36% of the candidate LIGO region. And they do claim an “excess of detected X-ray photons” coming from somewhere on the sky over the standard, average background. But when you look at the data yourself, you have to ask yourself: how compelling is this?

    7
    Three critical figures, showing the raw data of the alleged ‘signal’ along with the background of X-ray emissions observed by the AGILE satellite, from the recently submitted publication, AGILE Observations of the Gravitational Wave Source GW170104.

    Over a few seconds before-and-after the LIGO merger, they pulled out an interesting event that they identify as “E2” in the three charts above. After doing a full analysis, where they account for what they saw and what sort of random fluctuations and backgrounds just naturally occur, they can conclude that there’s about a 99.9% chance that something interesting happened. In other words, that they saw an actual signal of something, rather than a random fluctuation. After all, the Universe is full of objects that emit gamma rays and X-rays, and that’s what the background is made of. But was it related to the gravitational merger of these two black holes?

    7
    Computer simulation of two merging black holes producing gravitational waves. The big, unanswered question is whether there will be any sort of electromagnetic, light counterpart to this signal? Image credit: Werner Benger, cc by-sa 4.0.

    If it were, you’d expect other satellites to see it. The best we can conclude, so far, is that if black holes do have an electromagnetic counterpart, it’s one that’s:

    incredibly weak,
    that occurs mostly at lower energies,
    that doesn’t have a bright optical or radio or gamma-ray component,
    and that occurs with an offset to the actual emission of gravitational waves.

    8
    The 30-ish solar mass binary black holes first observed by LIGO are very difficult to form without direct collapse. Now that it’s been observed twice, these black hole pairs are thought to be quite common. But the question of electromagnetic emission from these mergers is not yet settled. Image credit: LIGO, NSF, A. Simonnet (SSU).

    Also, everything we see is perfectly consistent — and arguably, more consistent — with the notion that merging black holes don’t have any electromagnetic counterparts at all. But the truth about it all is that we don’t have sufficient data to decide just yet. With more gravitational wave detectors, more black hole mergers of high masses, better pinpointing of the location, and better all-sky coverage of transient events, we just might find out the answer to this. If the missions and observatories proposed to collect this data are successfully built, operated, and (where necessary) launched, then 15 years from now, we can expect to actually know the scientific answer for certain.

    See the full article here .

    Please help promote STEM in your local schools.

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    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

     
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