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  • richardmitnick 12:13 pm on June 15, 2021 Permalink | Reply
    Tags: "Gravitational waves confirm a black hole law predicted by Stephen Hawking", , , , Caltech/MIT Advanced aLigo, , , ,   

    From Science News : “Gravitational waves confirm a black hole law predicted by Stephen Hawking” 

    From Science News

    June 14, 2021
    Emily Conover

    The “area law” says that a black hole’s surface area cannot decrease over time.

    1

    Gravitational waves from two merging black holes (shown in a simulation), spotted in 2015, revealed that the total surface area of the black holes doesn’t decrease when they merge. Credit: Simulating Extreme Spacetimes project.

    Despite their mysterious nature, black holes are thought to follow certain simple rules. Now, one of the most famous black hole laws, predicted by physicist Stephen Hawking, has been confirmed with gravitational waves.

    According to the black hole area theorem, developed by Hawking in the early 1970s, black holes can’t decrease in surface area over time. The area theorem fascinates physicists because it mirrors a well-known physics rule that disorder, or entropy, can’t decrease over time. Instead, entropy consistently increases (SN: 7/10/15).

    That’s “an exciting hint that black hole areas are something fundamental and important,” says astrophysicist Will Farr of Stony Brook University (US) in New York and the Flatiron Institute (US) in New York City.

    The surface area of a lone black hole won’t change — after all, nothing can escape from within. However, if you throw something into a black hole, it will gain more mass, increasing its surface area. But the incoming object could also make the black hole spin, which decreases the surface area. The area law says that the increase in surface area due to additional mass will always outweigh the decrease in surface area due to added spin.

    To test this area rule, Massachusetts Institute of Technology (US) astrophysicist Maximiliano Isi, Farr and others used ripples in spacetime stirred up by two black holes that spiraled inward and merged into one bigger black hole. A black hole’s surface area is defined by its event horizon — the boundary from within which it’s impossible to escape. According to the area theorem, the area of the newly formed black hole’s event horizon should be at least as big as the areas of the event horizons of the two original black holes combined.

    The team analyzed data from the first gravitational waves ever spotted, which were detected by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, in 2015 (SN: 2/11/16).

    2
    SWEET SUCCESS For the first time, physicists have directly observed gravitational waves, caused by two black holes colliding (illustrated here). Credit:SXS – Simulating eXtreme Spacetimes (US).

    Caltech/MIT Advanced aLigo

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation.

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

    The researchers split the gravitational wave data into two time segments, before and after the merger, and calculated the surface areas of the black holes in each period. The surface area of the newly formed black hole was greater than that of the two initial black holes combined, upholding the area law with a 95 percent confidence level, the team reports in a paper to appear in Physical Review Letters.

    “It’s the first time that we can put a number on this,” Isi says.

    The area theorem is a result of the general theory of relativity, which describes the physics of black holes and gravitational waves. Previous analyses of gravitational waves have agreed with predictions of general relativity, and thus already hinted that the area law can’t be wildly off. But the new study “is a more explicit confirmation,” of the area law, says physicist Cecilia Chirenti of the University of Maryland (US) in College Park, who was not involved with the research.

    So far, general relativity describes black holes well. But scientists don’t fully understand what happens where general relativity — which typically applies to large objects like black holes — meets quantum mechanics, which describes small stuff like atoms and subatomic particles. In that quantum realm, strange things can happen.

    For example, black holes can release a faint mist of particles called Hawking radiation, another idea developed by Hawking in the 1970s. That effect could allow black holes to shrink, violating the area law, but only over extremely long periods of time, so it wouldn’t have affected the relatively quick merger of black holes that LIGO saw.

    Physicists are looking for an improved theory that will combine the two disciplines into one new, improved theory of quantum gravity. Any failure of black holes to abide by the rules of general relativity could point physicists in the right direction to find that new theory.

    So physicists tend to be grumpy about the enduring success of general relativity, Farr says. “We’re like, ‘aw, it was right again.’”

    See the full article here .


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  • richardmitnick 1:52 pm on March 12, 2021 Permalink | Reply
    Tags: "Giant gravitational wave detectors could hear murmurs from across universe", , , Caltech/MIT Advanced aLigo, European Space Agency(EU)/National Aeronautics and Space Administration (US) eLISA space based- the future of gravitational wave research., , KAGRA Large-scale Cryogenic Graviationai wave Telescope Project(JP), , ,   

    From Science Magazine: “Giant gravitational wave detectors could hear murmurs from across universe” 

    From Science Magazine

    Mar. 10, 2021
    Adrian Cho

    Just 5 years ago, physicists opened a new window on the universe when they first detected gravitational waves, ripples in space itself set off when massive black holes or neutron stars collide. Even as discoveries pour in, researchers are already planning bigger, more sensitive detectors. And a Ford versus Ferrari kind of rivalry has emerged, with scientists in the United States simply proposing bigger detectors, and researchers in Europe pursuing a more radical design.

    “Right now, we’re only catching the rarest, loudest events, but there’s a whole lot more, murmuring through the universe,” says Jocelyn Read, an astrophysicist at California State University, Fullerton(US), who’s working on the U.S. effort. Physicists hope to have the new detectors running in the 2030s, which means they have to start planning now, says David Reitze, a physicist at the California Institute of Technology(US). “Gravitational wave discoveries have captivated the world, so now is a great time to be thinking about what comes next.”

    Current detectors are all L-shaped instruments called interferometers. Laser light bounces between mirrors suspended at either end of each arm, and some of it leaks through to meet at the crook of the L. There, the light interferes in a way that depends on the arms’ relative lengths. By monitoring that interference, physicists can spot a passing gravitational wave, which will generally make the lengths of the arms waver by different amounts.

    Caltech/MIT Advanced aLigo


    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


    European Space Agency(EU)/National Aeronautics and Space Administration (US) eLISA space based, the future of gravitational wave research.

    To tamp down other vibrations, the interferometer must be housed in a vacuum chamber and the weighty mirrors hung from sophisticated suspension systems. And to detect the tiny stretching of space, the interferometer arms must be long. In the Laser Interferometer Gravitational-Wave Observatory (LIGO), twin instruments in Louisiana and Washington state that spotted the first gravitational wave from two black holes whirling into each other, the arms are 4 kilometers long. Europe’s Virgo detector in Italy has 3-kilometer-long arms.

    In spite of the detectors’ sizes, a gravitational wave changes the relative lengths of their arms by less than the width of a proton.

    The dozens of black hole mergers that LIGO and Virgo have spotted have shown that stellar-mass black holes, created when massive stars collapse to points, are more varied in mass than theorists expected.

    Masses in the Stellar Graveyard GWTC-2 plot v1.0 BY LIGO-Virgo. Credit: Frank Elavsky and Aaron Geller at Northwestern University(US).

    In 2017, LIGO and Virgo delivered another revelation, detecting two neutron stars spiraling together and alerting astronomers to the merger’s location on the sky. Within hours telescopes of all types had studied the aftermath of the resulting “kilonova,” observing how the explosion forged copious heavy elements.

    Researchers now want a detector 10 times more sensitive, which they say would have mind-boggling potential. It could spot all black hole mergers within the observable universe and even peer back to the time before the first stars to search for primordial black holes that formed in the big bang. It should also spot hundreds of kilonovae, laying bare the nature of the ultradense matter in neutron stars.

    The U.S. vision for such a dream machine is simple. “We’re just going to make it really, really big,” says Read, who is helping design Cosmic Explorer, an interferometer with arms 40 kilometers long—essentially, a LIGO detector scaled up 10-fold.

    The “cookie cutter design” might enable the United States to afford multiple, widely separated detectors, which would help pinpoint sources on the sky as LIGO and Virgo do now, says Barry Barish, a physicist at Caltech who directed the construction of LIGO.

    Siting such mammoth wave catchers may be tricky. The 40-kilometer arms have to be straight, but Earth is round. If the crook of the L sits on the ground, then the ends of the interferometers might have to rest on berms 30 meters high. So U.S. researchers hope to find bowl-like areas that might accommodate the structure more naturally.

    In contrast, European physicists envision a single subterranean gravitational wave observatory, called the Einstein Telescope [above], that would do it all. “We want to realize an infrastructure that is able to host all the evolutions [of detectors] for 50 years,” says Michele Punturo, a physicist with Italy’s National Institute for Nuclear Physics(IT) in Perugia and co-chair of the ET steering committee.

    The ET would comprise multiple V-shaped interferometers with arms 10 kilometers long, arranged in an equilateral triangle deep underground to help shield out vibrations. With interferometers pointed in three directions, the ET could determine the polarization of gravitational waves—the direction in which they stretch space—to help locate sources on the sky and probe the fundamental nature of the waves.

    The tunnels would actually house two sets of interferometers. The signals detected by LIGO and Virgo hum at frequencies that range from about 10 to 2000 cycles per second and rise as a pair of objects spirals together. But picking up lower frequencies of just a few cycles per second would open new realms. To detect them, a second interferometer that uses a lower power laser and mirrors cooled to near absolute zero would nestle in each corner of the ET. (Such mirrors are already in use at Japan’s KAGRA Large-scale Cryogenic Graviationai wave Telescope Project(JP) which has 3-kilometer arms and is striving to catch up with LIGO and Virgo.)

    By going to lower frequencies, the ET could detect the merger of black holes hundreds of times as massive as the Sun. It could also catch neutron-star pairs hours before they actually merge, giving astronomers advance warning of kilonova explosions, says Marica Branchesi, an astronomer at Italy’s Gran Sasso Science Institute. “The early emission [of light] is extremely important, because there is a lot of physics there,” she says.

    The ET should cost €1.7 billion, including €900 million for the tunneling and basic infrastructure, Punturo says. Researchers are considering two sites, one near where Belgium, Germany, and the Netherlands meet and another on the island of Sardinia. The plan is under review by the European Strategy Forum on Research Infrastructures, which could put the ET on its to-do list this summer. “This is an important political step,” Punturo says, but not final approval for construction.

    The U.S. proposal is less mature. Researchers want the National Science Foundation(US) to provide $65 million for design work so a decision on the billion-dollar machine can be made in the mid-2020s, Barish says. Physicists hope to have both Cosmic Explorer and the ET running in the mid-2030s, at the same time as the planned Laser Interferometer Space Antenna, a constellation of three spacecraft millions of kilometers apart that will sense gravitational waves of far lower frequencies from supermassive black holes in the centers of galaxies.

    Gravity is talking. Lisa will listen. Dialogos of Eide.

    European Space Agency(EU)/National Aeronautics and Space Administration (US) eLISA space based, the future of gravitational wave research.

    The push for new gravitational wave detectors isn’t necessarily a competition. “What we really want is to have ET and Cosmic Explorer and, ideally, even a third detector of similar sensitivity,” says Stefan Hild, a physicist at Maastricht University [Universiteit Maastricht](NL) who works on the ET. Reitze notes, however, that timing and cost could “push towards convergence and simplicity in designs.” Instead of a Ford and a Ferrari, perhaps physicists will end up building a few Audis.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • richardmitnick 12:06 am on March 9, 2021 Permalink | Reply
    Tags: "Establishing the Origin of Solar-Mass Black Holes and the Connection to Dark Matter", A definitive confirmation of the existence of black holes was celebrated with the 2020 physics Nobel Prize awarded to Andrea Ghez; Reinhard Genzel; and Roger Penrose., , , , , Caltech/MIT Advanced aLigo, , , Dark matter comprises the majority of matter in the Universe but its nature remains unknown., From Kavli Institute for the Physics and Mathematics of the Universe (IPMU) [カブリ数物連携宇宙研](JP) at U Tokyo {東京大学;Tōkyō daigaku](JP), Multiple gravitational wave detections of merging black holes have been identified by LIGO commemorated with the 2017 physics Nobel Prize to Kip Thorne; Barry Barish; and Rainer Weiss., What is the origin of black holes and how is that question connected with another mystery-the nature of Dark Matter?   

    From Kavli Institute for the Physics and Mathematics of the Universe (IPMU) [カブリ数物連携宇宙研](JP) at U Tokyo {東京大学;Tōkyō daigaku](JP) : “Establishing the Origin of Solar-Mass Black Holes and the Connection to Dark Matter” 

    KavliFoundation

    From Kavli Institute for the Physics and Mathematics of the Universe (IPMU) [カブリ数物連携宇宙研](JP) at U Tokyo {東京大学;Tōkyō daigaku](JP)

    Kavli IPMU

    March 5, 2021

    Research Contacts:
    Volodymyr Takhistov
    Project Researcher / Kavli IPMU Fellow
    Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
    volodymyr.takhistov@ipmu.jp

    George M. Fuller
    Distinguished Professor of Physics
    Director of Center for Astrophysics and Space Sciences
    Department of Physics, University of California, San Diego
    Email: gfuller@physics.ucsd.edu

    Alexander Kusenko
    Professor of Physics and Astronomy
    Department of Physics and Astronomy, University of California, Los Angeles,
    Visiting Senior Scientist
    Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
    kusenko@ucla.edu

    Media contact:
    John Amari
    Press officer
    Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo
    press@ipmu.jp

    1
    Fig.1: [Left] A tiny primordial black hole being captured by a neutron star, subsequently devouring it and leaving a “transmuted” solar-mass black hole remnant behind. [Right] Expected mass distribution of “transmuted” solar-mass black holes following neutron stars formed as a result of a delayed or a rapid supernova. The LIGO GW190814 event with 2.6 solar-mass black hole candidate is also shown. Credit: Takhistov et. al.)

    What is the origin of black holes and how is that question connected with another mystery-the nature of Dark Matter*? Dark matter comprises the majority of matter in the Universe but its nature remains unknown.

    Multiple gravitational wave detections of merging black holes have been identified within the last few years by the Laser Interferometer Gravitational-Wave Observatory (LIGO) commemorated with the 2017 physics Nobel Prize to Kip Thorne; Barry Barish; and Rainer Weiss.

    3
    Left to right: Rainer Weiss, Barry Barish and Kip Thorne, who have been awarded the 2017 Nobel prize in physics. Credit: Molly Riley/AFP/Getty Images.

    Artist’s by now iconic conception of two merging black holes similar to those detected by LIGO. Credit: Caltech/MIT aLigo/Aurore Simonnet/Sonoma State.

    Caltech/MIT Advanced aLigo


    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


    ESA/eLISA the future of gravitational wave research

    A definitive confirmation of the existence of black holes was celebrated with the 2020 physics Nobel Prize awarded to Andrea Ghez; Reinhard Genzel; and Roger Penrose. Understanding the origin of black holes has thus emerged as a central issue in physics.

    2
    Roger Penrose, Reinhard Genzel and Andrea Ghez have won the the 2020 Nobel Prize for Physics. (Courtesy: IOP Publishing/Tushna Commissariat; CC-BY-SA H Garching; UCLA/Christopher Dibble)

    Surprisingly, LIGO has recently observed a 2.6 solar-mass black hole candidate (event GW190814, reported in Astrophysical Journal Letters). Assuming this is a black hole, and not an unusually massive neutron star, where does it come from?

    Solar-mass black holes are particularly intriguing, since they are not expected from conventional stellar evolution astrophysics. Such black holes might arise in the early Universe (primordial black holes) or be “transmuted” from existing neutron stars. Some black holes could have formed in the early universe long before the stars and galaxies formed. Such primordial black holes could make up some part or all of dark matter. If a neutron star captures a primordial black hole, the black hole consumes the neutron star from the inside, turning it into a solar-mass black hole. This process can produce a population of solar mass black holes, regardless of how small the primordial black holes are. Other forms of dark matter can accumulate inside a neutron star causing its eventual collapse into a solar-mass black hole.

    A new study, published in Physical Review Letters, advances a decisive test to investigate the origin of solar-mass black holes. This work was led by the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Fellow Volodymyr Takhistov and the international team included George M. Fuller, Distinguished Professor of Physics and Director of the Center for Astrophysics and Space Science at the University of California, San Diego(US), as well as Alexander Kusenko, Professor of Physics and Astronomy at the University of California, Los Angeles(US) and a Kavli IPMU Visiting Senior Scientist.

    As the study discusses (see Fig. 1), “transmuted” solar-mass black holes remaining from neutron stars being devoured by dark matter (either tiny primordial black holes or particle dark matter accumulation) should follow the mass-distribution of the original host neutron stars. Since the neutron star mass distribution is expected to peak around 1.5 solar masses, it is unlikely that heavier solar-mass black holes have originated from dark matter interacting with neutron stars. This suggests that such events as the candidate detected by LIGO, if they indeed constitute black holes, could be of primordial origin from the early Universe and thus drastically affect our understanding of astronomy. Future observations will use this test to investigate and identify the origin of black holes.

    Previously (see Physical Review Letters ), the same international team of researchers also demonstrated that disruption of neutron stars by small primordial black holes can lead to a rich variety of observational signatures and can help us understand such long-standing astronomical puzzles as the origin of heavy elements (e.g. gold and uranium) and the 511 keV gamma-ray excess observed from the center of our Galaxy.

    *Dark Matter Background
    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, some 30 years later, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com.


    Coma cluster via NASA/ESA Hubble.


    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL).


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Kavli Institute for the Physics and Mathematics of the Universe (IPMU) [カブリ数物連携宇宙研](JP) at U Tokyo {東京大学;Tōkyō daigaku](JP) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/

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

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

     
  • richardmitnick 12:32 pm on February 25, 2021 Permalink | Reply
    Tags: "Pulsars- pulsing with astrophysics", A subset of these neutron stars soldier on as even wilder objects dubbed pulsars., , , , Caltech/MIT Advanced aLigo, , , In a universe chock-full of bizarre objects neutron stars rank near the top of the list., , , The pulsar known as SXP 1062   

    From The Kavli Foundation: “Pulsars- pulsing with astrophysics” 

    KavliFoundation

    From The Kavli Foundation

    1
    In this composite image, X-rays from Chandra and XMM-Newton have been colored blue and optical data from the NOIRLab Cerro Tololo Inter-American Observatory in Chile are colored red and green. The pulsar known as SXP 1062, is the bright white source located on the right-hand side of the image in the middle of the diffuse blue emission inside a red shell. The diffuse X-rays and optical shell are both evidence of a supernova remnant surrounding the pulsar. The optical data also displays spectacular formations of gas and dust in a star-forming region on the left side of the image. Image Credit: NASA/CXC/Univ.of Potsdam/L. Oskinova et al.

    NASA Chandra X-ray Space Telescope.

    ESA/XMM Newton X-ray telescope (EU).

    NOIRLab CTIO Cerro Tololo Inter-American Observatory, approximately 80 km to the East of La Serena, Chile, at an altitude of 2200 meters.

    In a universe chock-full of bizarre objects neutron stars rank near the top of the list. Although merely the size of a city, pulsars still pack in about one-and-a-half times the mass of our entire Sun.

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Neutron stars manage to pull off this feat because their extreme gravity crushes atoms so tightly that the atoms’ protons and electrons fuse together, forming a hyperdense object composed almost entirely of neutrons (hence the moniker). Even the origin of neutron stars is intense—they’re forged when colossal stars cataclysmically explode as supernovae and the dying monster star’s pure iron core collapses in on itself.

    For reasons not well-understood, a subset of these neutron stars soldier on as even wilder objects dubbed pulsars. These are neutron stars that spin anywhere from once every few seconds to many hundreds of times per second, sending beams of radiation sweeping through the cosmos like hyper lighthouses.

    Measuring the characteristics of those beams is one of the main ways researchers are keying in on how neutron stars and pulsars alike work, in turn helping probe the boundaries of fundamental physics.

    “Pulsar emissions are the primary signature of neutron stars, and neutron stars represent the most extreme matter in the observable universe,” says Roger Romani, a professor of physics at Stanford University(US) and a member of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC).

    Romani and colleagues are keenly interested in the dividing line between neutron stars and the only objects made of even denser material, namely stellar black holes. (And which are not part of the “observable” universe, seeing as they do not emit light.) Stellar black holes form the same way as neutron stars, when ginormous stars go boom, though in the former’s case, the leftover stellar cinder compacts so tightly that its gravity traps light, and the object goes “dark.”

    The dividing line is one of mass, where the most massive stars yield the most massive cores that, at some threshold, generate the gravity necessary to progress past neutron-starhood and into black holiness. (Forgive the punnery.) Researchers want to better understand this boundary and reap the insights it will provide into how matter behaves in conditions completely unreplicable on Earth.

    “I’ve been chasing down where the neutron star – black hole boundary is,” says Romani. “How massive can a neutron star get before it disappears, collapsing into a black hole?”

    Pulsars are in fact paving the way to this understanding, specifically a kind of pulsar with the ominous nickname “black widow.” These are pulsars that steadily destroy companion stars with energetic outflows, oftentimes gravitationally slurping up some of the scattered matter from their victims. (The nickname derives from how female black widow spiders tend to eat their male partners, an act that gave the spiders their evocative appellation in the first place.) The rate of pulses from some black widow pulsars suggest they’ve have gobbled up so much matter that they’re at the “brink of collapse,” Romani says, and could transition into being black holes.

    Other important insights into neutron star physics will come via gravitational wave astronomy. It’s a field that sprung to life just six years ago with the announcement of the first-ever direct detection of gravitational waves by the LIGO observatory (led in part by members of the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology).

    Kavli MIT Institute For Astrophysics and Space Research.



    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

    As LIGO and its ilk capture more events in the years ahead spawned by the energetic mergers of neutron stars, as well as black holes and neutron stars, astrophysicists will gain a vital new dataset. “Gravitational wave signatures can also help once we get a large sample of neutron star-containing mergers,” Romani says.

    Also helpful will be pulsar pulses not of the usual radio-wave variety measured in abundance since the discovery of pulsars in 1967. “For the radio emission, we are flooded in data,” says Romani. “But most of it is ‘weather’ and it is hard to see how we will cut through this to probe the underlying physics.”

    Instead, harder-to-corral, higher-energy light, such as gamma rays and x-rays, is now broadening our understanding of the mechanisms driving pulsars.

    “For the extreme physics questions, additional measurements of neutron star masses, radii, and surface emissions, especially in the x-ray band, offer good hope of near-future progress,” says Romani.

    The KIPAC researcher expects this wealth of data will help answer one of the biggest outstanding mystery about pulsars—how the heck do they generate their telltale radio pulses, anyway? “Some plausible models have been proposed,” Romani says. “But there is as yet no generally accepted picture.”

    It goes to show that while neutron stars and pulsars are pushing astrophysics into new frontiers, some age-old, basic questions about these extraordinary objects still need answering.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

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

    The Kavli Foundation, based in Los Angeles, California, is a foundation that supports the advancement of science and the increase of public understanding and support for scientists and their work.

    The Kavli Foundation was established in December 2000 by its founder and benefactor, Fred Kavli, a Norwegian business leader and philanthropist, who made his money by creating Kavlico, a company that made sensors, and by investing in real estate in southern California and Nevada. David Auston, a former president of Case Western Reserve University and former Bell Labs scientist, was the first president of the Kavli Foundation and is largely credited with the vision of the scientific investments. Kavli died in 2013, and his foundation is currently actively involved in establishing research institutes at universities throughout the United States, in Europe, and in Asia.

    To date, the Kavli Foundation has made grants to establish Kavli Institutes on the campuses of 16 major universities. In addition to the Kavli Institutes, six Kavli professorships have been established: two at University of California, Santa Barbara, one each at University of California, Los Angeles, University of California, Irvine, Columbia University, Cornell University, and California Institute of Technology.

     
  • richardmitnick 2:58 pm on February 11, 2021 Permalink | Reply
    Tags: "Hubble Uncovers Concentration of Small Black Holes", A gravitational pinball game takes place inside globular clusters., , , , Because a black hole cannot be seen they carefully studied the motion of stars inside the cluster., , Caltech/MIT Advanced aLigo, , Hubble researchers went hunting for an IMBH in the nearby globular cluster NGC 6397., Intermediate-mass black holes (IMBHs) have been elusive., , NGC 6397 is a core-collapsed cluster., The amount of mass a black hole can pack away varies widely from less than twice the mass of our Sun to over a billion times our Sun's mass., The central black holes may eventually merge sending ripples across space as gravitational waves., The study led to the conclusion that there is not just one hefty black hole but a swarm of smaller black holes – a mini-cluster in the core of the globular., This game of stellar pinball is called "dynamical friction" where heavier stars are segregated in the cluster's core and lower-mass stars migrate to the cluster's periphery.   

    From NASA/ESA Hubble Telescope: “Hubble Uncovers Concentration of Small Black Holes” 

    NASA/ESA Hubble Telescope


    From NASA/ESA Hubble Telescope

    February 11, 2021

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    Bethany Downer
    ESA/Hubble Space Telescope
    bethany.downer@esahubble.org

    Science Contacts:
    Eduardo Vitral
    Institut d’Astrophysique de Paris (IAP)(FR)
    vitral@iap.fr

    Dr. Gary A. Mamon
    Institut d’Astrophysique de Paris (IAP) (FR)
    gam@iap.fr

    1
    Compass Image for NGC 6397
    Credits: Image: NASA/ESA, T. Brown, S. Casertano, and J. Anderson (STScI) (US)
    Science: NASA/ ESA E. Vitral and G. Mamon (Institut d’Astrophysique de Paris (IAP) (FR)

    Summary

    The idea that black holes come in different sizes may sound a little odd at first. After all, a black hole by definition is an object that has collapsed under gravity to an infinite density, making it smaller than the period at the end of this sentence. But the amount of mass a black hole can pack away varies widely from less than twice the mass of our Sun to over a billion times our Sun’s mass. Midway between are intermediate-mass black holes (IMBHs) weighing roughly hundreds to tens of thousands of solar masses. So, black holes come small, medium, and large.

    However, the IMBHs have been elusive. They are predicted to hide out in the centers of globular star clusters, beehive-shaped swarms of as many as a million stars. Hubble researchers went hunting for an IMBH in the nearby globular cluster NGC 6397 and came up with a surprise. Because a black hole cannot be seen, they carefully studied the motion of stars inside the cluster, that would be gravitationally affected by the black hole’s gravitational tug. The amplitudes and shapes of the stellar orbits led to the conclusion that there is not just one hefty black hole, but a swarm of smaller black holes – a mini-cluster in the core of the globular.

    Why are the black holes hanging out together? A gravitational pinball game takes place inside globular clusters where more massive objects sink to the center by exchanging momentum with smaller stars, that then migrate to the cluster’s periphery. The central black holes may eventually merge, sending ripples across space as gravitational waves.

    ________________________________________________________________________________________________________

    Astronomers found something they weren’t expecting at the heart of the globular cluster NGC 6397: a concentration of smaller black holes lurking there instead of one massive black hole.

    Globular clusters are extremely dense stellar systems, which host stars that are closely packed together. These systems are also typically very old — the globular cluster at the focus of this study, NGC 6397, is almost as old as the universe itself. This cluster resides 7,800 light-years away, making it one of the closest globular clusters to Earth. Due to its very dense nucleus, it is known as a core-collapsed cluster.

    At first, astronomers thought the globular cluster hosted an intermediate-mass black hole (IMBH). These IMBHs are the long-sought “missing link” between supermassive black holes (many millions of times our Sun’s mass) that lie at the cores of galaxies, and stellar-mass black holes (a few times our Sun’s mass) that form following the collapse of a single massive star. Their mere existence is hotly debated. Only a few candidates have been identified to date.

    “We found very strong evidence for an invisible mass in the dense core of the globular cluster, but we were surprised to find that this extra mass is not ‘point-like’ (that would be expected for a solitary massive black hole) but extended to a few percent of the size of the cluster,” said Eduardo Vitral of the Paris Institute of Astrophysics, (IAP) (FR).

    To detect the elusive hidden mass, Vitral and Gary Mamon, also of IAP, used the velocities of stars in the cluster to determine the distribution of its total mass, that is the mass in the visible stars, as well as in faint stars and black holes. The more mass at some location, the faster the stars travel around it.

    The researchers used previous estimates of the stars’ tiny proper motions (their apparent motions on the sky), which allow for determining their true velocities within the cluster. These precise measurements for stars in the cluster’s core could only be made with Hubble over several years of observation. The Hubble data were added to well-calibrated proper motion measurements provided by the European Space Agency’s Gaia space observatory, but which are less precise than Hubble’s observations in the core.

    ESA (EU)/GAIA satellite .

    “Our analysis indicated that the orbits of the stars are close to random throughout the globular cluster, rather than systematically circular or very elongated,” explained Mamon. These moderate-elongation orbital shapes constrain what the inner mass must be.

    The researchers conclude that the invisible component can only be made of the remnants of massive stars (white dwarfs, neutron stars, and black holes) given its mass, extent and location. These stellar corpses progressively sank to the cluster’s center after gravitational interactions with nearby less massive stars. This game of stellar pinball is called “dynamical friction,” where, through an exchange of momentum, heavier stars are segregated in the cluster’s core and lower-mass stars migrate to the cluster’s periphery.

    “We used the theory of stellar evolution to conclude that most of the extra mass we found was in the form of black holes,” said Mamon. Two other recent studies had also proposed that stellar remnants, in particular, stellar-mass black holes, could populate the inner regions of globular clusters. “Ours is the first study to provide both the mass and the extent of what appears to be a collection of mostly black holes in the center of a core-collapsed globular cluster,” added Vitral [Astronomy & Astrophysics].

    The astronomers also note that this discovery raises the possibility that mergers of these tightly packed black holes in globular clusters may be an important source of gravitational waves, ripples through spacetime. Such phenomena could be detected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) experiment. LIGO is funded by the National Science Foundation and operated by Caltech and MIT.

    MIT /Caltech Advanced aLigo .

    See the full article here.


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    Major Instrumentation

    Wide Field Camera 3 [WFC3]

    NASA/ESA Hubble WFC3

    Advanced Camera for Surveys [ACS]

    NASA Hubble Advanced Camera for Surveys.

    Cosmic Origins Spectrograph [COS]

    NASA Hubble Cosmic Origins Spectrograph.

    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 3:45 pm on January 21, 2021 Permalink | Reply
    Tags: An X-ray signal is unexpectedly lingering., , , , Caltech/MIT Advanced aLigo, , Kilonova explosions, , NASA's Goddard Space Flight Center in Maryland, , Three years ago two neutron stars collided in a cataclysmic crash.,   

    From University of Maryland via Live Science: “A neutron-star crash spotted 3 years ago is still pumping out X-rays. But why?” 


    From University of Maryland

    via

    Live Science

    1.21.21
    Meghan Bartels

    1
    An artist’s depiction of X-ray emissions forming the last afterglow of the high-energy jets produced by a neutron-star collision. © NASA’s Goddard Space Flight Center/CI Lab.

    Three years ago, two neutron stars collided in a cataclysmic crash, the first such merger ever observed directly. Naturally, scientists kept their eye on it — and now, something strange is happening.

    Astrophysicists observed the star collision on Aug. 17, 2017, spotting for the first time ever signs of the same event in both a gravitational-wave chirp detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) on Earth and a massive burst of different flavors of light.

    MIT /Caltech Advanced aLigo .

    The X-rays observed at the location 130 million light-years from Earth peaked less than six months after the merger’s discovery, then began to fade. But in observations gathered this year, that trend has stopped, and an X-ray signal is unexpectedly lingering, according to research presented on Thursday (Jan. 14) at the 237th meeting of the American Astronomical Society, held virtually due to the pandemic.

    “Our models so far were describing the observation incredibly well, so we thought we nailed it down,” Eleonora Troja, an astrophysicist at the University of Maryland and NASA’s Goddard Space Flight Center in Maryland, told Space.com. “I think everybody was convinced that this thing was going to fade quickly, and the last observation showed that it is not.”

    A star crash checkup … and mystery

    When NASA’s Chandra X-ray Observatory checked in on the former merger in the spring, things were beginning to look fishy.

    NASA Chandra X-ray Space Telescope.

    Scientists thought they were looking at the afterglow of the high-energy jet of material shot out by the collision, and they had expected the X-rays to have faded by the spring. But the source was still glowing in the spacecraft’s view. When the telescope looked again, in December, it still found a bright X-ray signal.

    It’s too early to know what precisely is happening, Troja said. Chandra may not look again until this December, although she plans to ask for the telescope to change plans to check in sooner. Radio instruments can study the collision more frequently, and could help solve the puzzle between now and then.

    For now, Troja believes one of two hypotheses will explain the continued X-ray emissions.

    In one scenario, the lingering X-rays are joined by radio light within the next eight months or year. Troja said that would suggest that scientists are seeing not the afterglow of jets shooting out from the collision, but the afterglow of the massive kilonova explosion itself — something scientists have never seen before.

    3
    An artist’s depiction of a cloud of debris created by a neutron-star collision. Credit: NASA’s Goddard Space Flight Center/CI Lab.

    “People think that in the 21st century we have seen it all and there is no first time left,” she said. Not so if this hypothesis holds. “This would be a first, it would be a new type of light, a new form of astrophysical source that we have never seen before.”

    If the X-ray emissions continue but no radio emissions join them, Troja thinks scientists may be looking at something perhaps still more intriguing: proof that the collision formed a massive neutron star, the most massive such object known to date.

    Soon after the collision, scientists calculated the mass of the initial neutron stars and the mass of what was left, after the dramatics shot matter out into space. But that value is between the current largest known neutron star and the smallest known black hole, leaving scientists stumped. The new observations could decide it: If the object is emitting X-rays, it sure isn’t a black hole. Confirming the result of the collision would give scientists an opportunity to better understand how matter behaves in superdense neutron stars, she said.

    “We have a beautiful problem,” Troja said. “No matter what the solution is, it’s going to be exciting, which is a great problem to have in astrophysics.”

    See the full article here .

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    Driven by the pursuit of excellence, the University of Maryland has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

    The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

    Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

     
  • richardmitnick 9:03 am on January 19, 2021 Permalink | Reply
    Tags: "Missing- One Black Hole With 10 Billion Solar Masses", , , , , Caltech/MIT Advanced aLigo, , The galaxy A2261-BCG,   

    From The New York Times: “Missing- One Black Hole With 10 Billion Solar Masses” 

    From The New York Times

    Jan. 19, 2021
    Dennis Overbye

    One of the biggest galaxies in the universe seems to lack its dark centerpiece.

    1
    The galaxy cluster Abell 2261, captured by the Hubble Space Telescope. The brightest galaxy, center left, is about one million light-years across and about 10 times the diameter of the Milky Way.Credit: NASA/ESA Hubble, M. Postman (STScI), T. Lauer (NOIRLab/NOAO), and the CLASH team.

    Astronomers are searching the cosmic lost-and-found for one of the biggest, baddest black holes thought to exist. So far they haven’t found it.

    In the past few decades, it has become part of astronomical lore, if not quite a law, that at the center of every luminous city of light, called a galaxy, lurks something like a hungry Beelzebub, a giant black hole into which the equivalent of millions or even billions of suns have disappeared. The bigger the galaxy, the more massive the black hole at its center.

    So it was a surprise a decade ago when Marc Postman, of the Space Telescope Science Institute, using the Hubble Space Telescope to survey clusters of galaxies, found a supergiant galaxy [The Astrophysical Journal] with no sign of a black hole in its center. Normally, the galaxy’s core would have a kink of extra light in its center, a kind of sparkling cloak, produced by stars that had been gathered there by the gravity of a giant black hole.

    On the contrary, at the exact center of the galaxy’s wide core, where a slight bump in starlight should have been, there was a slight dip. Moreover, the entire core, a cloud of stars some 20,000 light years across, was not even centered on the exact middle of the galaxy.

    “Oh, my God, this is really unusual,” Tod Lauer, an expert on galactic nuclei at the NOIRLab National Optical Astronomy Observatory in Tucson, Ariz., and an author on the paper, recalled saying when Dr. Postman showed him the finding.

    Kitt Peak NOIRLab National Observatory of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers 55 mi west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft), annotated.

    That was in 2012. In the years since, the two researchers and their colleagues have been ransacking the galaxy, looking for X-rays or radio waves from the missing black hole.

    The galaxy is the brightest one in a cluster known as Abell 2261. It is about 2.7 billion light-years from here, in the constellation Hercules in the northern sky, not far from the prominent star Vega. Using the standard rule of thumb, the black hole missing from the center of the 2261 galaxy should be 10 billion solar masses or more, comparable to the mightiest of these monsters known to astronomers. The black hole at the center of the Milky Way galaxy is only about four million solar masses.

    SGR A and SGR A* from Penn State and NASA/Chandra.


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

    So where has nature stashed the equivalent of 10 billion suns?

    One possibility is that the black hole is there but has gone silent, having temporarily run out of anything to eat. But another provocative possibility, Dr. Lauer and his colleagues say, is that the black hole was thrown out of the galaxy altogether.

    ‘A pit in every peach’

    Proving the latter could provide insight into some of the most violent and dynamic processes in the evolution of galaxies and the cosmos, about which astronomers have theorized but never seen — a dance of titanic forces and swirling worlds that can fling stars and planets across the void.

    “It’s an intriguing mystery, and we’re on the case,” Dr. Postman said in an email. He added that the upcoming James Webb Space Telescope would have the capability to shed light, so to speak, on the case.

    “What happens when you eject a supermassive black hole from a galaxy?” Dr. Lauer asked.

    “The story of A2261-BCG,” he said, referring to the galaxy’s formal name in literature, “is what happens with the most massive galaxies in the universe, the giant elliptical galaxies, at the end point of galaxy evolution.”

    Dr. Lauer is part of an informal group who call themselves Nukers. The group, whose membership is fluid — “like a band,” he said — first came together under Sandra Faber of the University of California, Santa Cruz, in the early days of the Hubble Space Telescope. Over the past four decades, they have sought to elucidate the nature of galactic nuclei, using the sharp eye of Hubble and other new facilities to peer into the intimate hearts of distant galaxies.

    2
    Radio emissions detected near the center of the galaxy suggested supermassive black hole activity had taken place there 50 million years ago.Credit: NASA/CXC, NASA/STScI, NAOJ/Subaru, NSF/NRAO/VLA.

    NASA Chandra X-ray Space Telescope.

    NASA/ESA Hubble Telescope.

    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level.

    NRAO Karl G Jansky Very Large Array, located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes.

    Black holes are objects so dense that not even light can escape their gravitational clutches. They are invisible by definition, but the ruckus — X-rays and radio screams — caused by material falling into its grasp can be seen across the universe. The discovery in the 1960s of quasars in the centers of galaxies first led astronomers to consider that supermassive black holes were responsible for such fireworks.

    By the turn of the century, astronomers had come to the conclusion that every galaxy harbored a supermassive black hole, millions to billions of times more massive than the sun, in its bosom. Where they came from — whether they grew from smaller black holes that had formed from the collapse of stars, or formed through some other process early in the universe — nobody is sure. “There is a pit in every peach,” Dr. Lauer said.

    But how do these entities affect their surroundings?

    In 1980, three astronomers, Mitchell Begelman, Martin Rees and Roger Blandford, wrote about how these black holes would alter the evolution of the galaxies they inhabit. When two galaxies collided and merged — an especially common event in the earlier universe — their central black holes would meet and form a binary system, two black holes circling each other.

    Dr. Begelman and his colleagues argued that these two massive black holes, swinging around, would interact with the sea of stars they were immersed in. Every once in a while, one of these stars would have a close encounter with the binary, and gravitational forces would push the star out of the center, leaving the black holes even more tightly bound.

    Over time, more and more stars would be tossed away from the center. Gradually, starlight that was once concentrated at the center would spread out into a broader, diffuse core, with a little kink at the center where the black-hole binary was doing its mating dance. The process is called “scouring.”

    “They were way ahead of the game,” Dr. Lauer said of the three astronomers.

    A knotty problem

    A scoured core was the kind of situation that Dr. Lauer and Dr. Postman thought they had encountered with Abell 2261. But instead of a peak at the center of the core, there was a dip, as if the supermassive black hole and its attendant stars had simply been taken away.

    This raised the even more dramatic possibility that the scenario envisioned by Dr. Begelman and his colleagues had played out all the way to the end: The two black holes had merged into one gigantic mouthful of nothing. The merger would have been accompanied by a cataclysmic burst of gravitational waves, space-time ripples predicted to exist by Einstein in 1916 and finally seen by the LIGO instruments a century later, in 2016.


    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

    If that burst was lopsided, it would have sent the resultant supermassive black hole flying through the galaxy, or even out of it, something astronomers had never observed. So finding the errant black hole was of the utmost importance.

    Further scrutiny of A2261-BCG revealed four little knots of light within the diffuse core. Could one of them be harboring the black hole?

    A team led by Sarah Burke-Spolaor of West Virginia University took to the sky with Hubble [above] and the Very Large Array [above] radio telescope in Socorro, New Mexico. Spectroscopic measurements by the Hubble could tell how fast the stars in the knots were jiggling around, and thus whether some massive object — a black hole — was needed to keep them all together.

    Two of the knots, they concluded, were probably small galaxies with small internal motions being cannibalized by the big galaxy. Measurements of the third knot had such large error bars that it could not yet be ruled in or out as the black hole’s location.

    The fourth, very compact knot near the bottom edge of the core was too faint even for the Hubble, Dr. Burke-Spoloar reported. “Observing this knot would have required an overblown amount of time (hundreds of hours) observing with Hubble Space Telescope,” she said in an email, and so it also remains a candidate for the black-hole hiding spot.

    The galaxy core also emits radio waves, but they didn’t help the search, Dr. Burke-Spolaor said.

    “We were originally hoping the radio emission would be some kind of literal smoking gun, showing an active jet that points directly back to black-hole location,” she said. But the radio relic was at least 50 million years old, according to its spectral characteristics, which meant, she said, that the large black hole would have had ample time to move elsewhere since the jet turned off.

    Next stop was NASA’s orbiting Chandra X-ray Observatory [above]. Kayhan Gultekin of the University of Michigan, another veteran Nuker who was not on the original discovery team, aimed the telescope at the cluster core and those suspicious knots. No dice. The putative black hole would have to be feeding at one-millionth of its potential rate if it were there at all, Dr. Gultekin said.

    “Either any black hole at the center is very faint, or it isn’t there,” he wrote in an email. The same goes for the case of a binary black-hole system, he said; it would need to be eating very little gas to stay hidden.

    In the meantime, Imran Nasim, of the University of Surrey in the U.K., who was not part of Dr. Postman’s team, has published a detailed analysis [MNRAS] of how the merger of two supermassive black holes could reform the galaxy into what the astronomers have found.

    “Simply, gravitational wave recoil ‘kicks’ the supermassive black hole out of the galaxy,” Dr. Nasim explained in an email. Having lost its supermassive anchor, the cloud of stars around the black hole binary spreads out, becoming more diffuse. The density of stars in that region — the densest part of the entire giant galaxy — is only one-tenth the density of stars in our own neighborhood of the Milky Way, resulting in a night sky that would appear anemic compared with our own.

    All this is another reason that astronomers eagerly await the launch of the James Webb Space Telescope, the long-awaited successor to Hubble, which is now scheduled for the end of October. That telescope will be able to examine all four knots at the same time and determine whether any of them are a cloaked, supermassive black hole.

    “Here you see our great sophistication,” Dr. Lauer said. “Hey! Maybe it’s in the knots! — Hey maybe it isn’t! Better search everything!”

    See the full article here .

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  • richardmitnick 4:46 pm on January 7, 2021 Permalink | Reply
    Tags: "After decades of effort scientists are finally seeing black holes—or are they?, , , Caltech/MIT Advanced aLigo, , , , Richard Genzel-MPE,   

    From Science Magazine: “After decades of effort scientists are finally seeing black holes—or are they? 

    From Science Magazine

    Jan. 7, 2021
    Adrian Cho

    1
    General relativity makes very specific predictions about what black holes are and how they should appear, as shown in this simulation. Credit: GODDARD SPACE FLIGHT CENTER/JEREMY SCHNITTMAN.

    While working on his doctorate in theoretical physics in the early 1970s, Saul Teukolsky solved a problem that seemed purely hypothetical. Imagine a black hole, the ghostly knot of gravity that forms when, say, a massive star burns out and collapses to an infinitesimal point. Suppose you perturb it, as you might strike a bell. How does the black hole respond?

    Teukolsky, then a graduate student at the California Institute of Technology (Caltech), attacked the problem with pencil, paper, and Albert Einstein’s theory of gravity, general relativity. Like a bell, the black hole would oscillate at one main frequency and multiple overtones, he found. The oscillations would quickly fade as the black hole radiated gravitational waves—ripples in the fabric of space itself. It was a sweet problem, says Teukolsky, now at Cornell University. And it was completely abstract—until 5 years ago.

    In February 2016, experimenters with the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of huge instruments in Louisiana and Washington, reported the first observation of fleeting gravitational ripples, which had emanated from two black holes, each about 30 times as massive as the Sun, spiraling into each other 1.3 billion light-years away.


    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

    LIGO even sensed the “ring down”: the shudder of the bigger black hole produced by the merger. Teukolsky’s old thesis was suddenly cutting-edge physics.

    The thought that anything I did would ever have implications for anything measurable in my lifetime was so far-fetched that the last 5 years have seemed like living in a dream world,” Teukolsky says. “I have to pinch myself, it doesn’t feel real.”

    Fantastical though it may seem, scientists can now study black holes as real objects. Gravitational wave detectors have spotted four dozen black hole mergers since LIGO’s breakthrough detection. In April 2019, an international collaboration called the Event Horizon Telescope (EHT) produced the first image of a black hole. By training radio telescopes around the globe on the supermassive black hole in the heart of the nearby galaxy Messier 87 (M87), EHT imaged a fiery ring of hot gas surrounding the black hole’s inky “shadow.”

    Messier 87*, The first image of the event horizon of a black hole. This is the supermassive black hole at the center of the galaxy Messier 87. Image via JPL/ Event Horizon Telescope Collaboration released on 10 April 2019.

    EHT map.

    Meanwhile, astronomers are tracking stars that zip close to the black hole in the center of our own Galaxy, following paths that may hold clues to the nature of the black hole itself.

    The observations are already challenging astrophysicists’ assumptions about how black holes form and influence their surroundings. The smaller black holes detected by LIGO and, now, the European gravitational wave detector Virgo in Italy have proved heavier and more varied than expected, straining astrophysicists’ understanding of the massive stars from which they presumably form. And the environment around the supermassive black hole in our Galaxy appears surprisingly fertile, teeming with young stars not expected to form in such a maelstrom. But some scientists feel the pull of a more fundamental question: Are they really seeing the black holes predicted by Einstein’s theory?

    Some theorists say the answer is most likely a ho-hum yes. “I don’t think we’re going to learn anything more about general relativity or the theory of black holes from any of this,” says Robert Wald, a gravitational theorist at the University of Chicago. Others aren’t so sure. “Are black holes strictly the same as you would expect with general relativity or are they different?” asks Clifford Will, a gravitational theorist at the University of Florida. “That’s going to be a major thrust of future observations.” Any anomalies would require a rethink of Einstein’s theory, which physicists suspect is not the final word on gravity, as it doesn’t jibe with the other cornerstone of modern physics, quantum mechanics.

    Using multiple techniques, researchers are already gaining different, complementary views of these strange objects, says Andrea Ghez, an astrophysicist at the University of California, Los Angeles, who shared the 2020 Nobel Prize in Physics for inferring the existence of the supermassive black hole in the heart of our Galaxy. “We’re still a long way from putting a complete picture together,” she says, “but we’re certainly getting more of the puzzle pieces in place.”

    Andrea Ghez has centered her work at the W.M Keck Observatory.

    W.M. Keck Observatory, two ten meter telescopes operated by Caltech and the University of California, Maunakea Hawaii USA, altitude 4,207 m (13,802 ft). Credit: Caltech.

    Consisting of pure gravitational energy, a black hole is a ball of contradictions. It contains no matter, but, like a bowling ball, possesses mass and can spin. It has no surface, but has a size. It behaves like an imposing, weighty object, but is really just a peculiar region of space.

    Or so says general relativity, which Einstein published in 1915. Two centuries earlier, Isaac Newton had posited that gravity is a force that somehow reaches through space to attract massive objects to one another. Einstein went deeper and argued that gravity arises because massive things such as stars and planets warp space and time—more accurately, spacetime—causing the trajectories of freely falling objects to curve into, say, the parabolic arc of a thrown ball.

    Early predictions of general relativity differed only slightly from those of Newton’s theory. Whereas Newton predicted that a planet should orbit its star in an ellipse, general relativity predicts that the orientation of the ellipse should advance slightly, or precess, with each orbit. In the first triumph of the theory, Einstein showed it accounted for the previously unexplained precession of the orbit of the planet Mercury. Only years later did physicists realize the theory also implied something far more radical.

    In 1939, theorist J. Robert Oppenheimer and colleagues calculated that when a sufficiently massive star burned out, no known force could stop its core from collapsing to an infinitesimal point, leaving behind its gravitational field as a permanent pit in spacetime. Within a certain distance of the point, gravity would be so strong that not even light could escape. Anything closer would be cut off from the rest of the universe, David Finkelstein, a theorist at Caltech, argued in 1958. This “event horizon” isn’t a physical surface. An astronaut falling past it would notice nothing special. Nevertheless, reasoned Finkelstein, who died just days before LIGO’s announcement in 2016, the horizon would act like a one-way membrane, letting things fall in, but preventing anything from getting out.

    According to general relativity, these objects—eventually named black holes by famed theorist John Archibald Wheeler—should also exhibit a shocking sameness. In 1963, Roy Kerr, a mathematician from New Zealand, worked out how a spinning black hole of a given mass would warp and twist spacetime. Others soon proved that, in general relativity, mass and spin are the only characteristics a black hole can have, implying that Kerr’s mathematical formula, known as the Kerr metric, describes every black hole there is. Wheeler dubbed the result the no-hair theorem to emphasize that two black holes of the same mass and spin are as indistinguishable as bald pates. Wheeler himself was bald, Teukolsky notes, “so maybe it was bald pride.”

    Some physicists suspected black holes might not exist outside theorists’ imaginations, says Sean Carroll, a theorist at Caltech. Skeptics argued that black holes might be an artifact of general relativity’s subtle math, or that they might only form under unrealistic conditions, such as the collapse of a perfectly spherical star. However, in the late 1960s, Roger Penrose, a theorist at the University of Oxford, dispelled such doubts with rigorous math, for which he shared the 2020 Nobel Prize in Physics. “Penrose exactly proved that, no, no, even if you have a lumpy thing, as long as the density became high enough, it was going to collapse to a black hole,” Carroll says.

    Soon enough, astronomers began to see signs of actual black holes. They spotted tiny x-ray sources, such as Cygnus X-1, each in orbit around a star. Astrophysicists deduced that the x-rays came from gas flowing from the star and heating up as it fell onto the mysterious object. The temperature of the gas and the details of the orbit implied the x-ray source was too massive and too small to be anything but a black hole. Similar reasoning suggested quasars, distant galaxies spewing radiation, are powered by supermassive black holes in their centers.

    But no one could be sure those black holes actually are what theorists had pictured, notes Feryal Özel, an astrophysicist at the University of Arizona (UA). For example, “Very little that we have done so far establishes the presence of an event horizon,” she says. “That is an open question.”

    Now, with multiple ways to peer at black holes, scientists can start to test their understanding and look for surprises that could revolutionize physics. “Even though it’s very unlikely, it would be so amazingly important if we found that there was any deviation” from the predictions of general relativity, Carroll says. “It’s a very high-risk, high-reward question.”

    Scientists hope to answer three specific questions: Do the observed black holes really have event horizons? Are they as featureless as the no-hair theorem says? And do they distort spacetime exactly as the Kerr metric predicts?

    Perhaps the simplest tool for answering them is one that Ghez developed. Since 1995, she and colleagues have used the 10-meter Keck telescope in Hawaii to track stars around a radio source known as Sagittarius A* (Sgr A*) in the center of our Galaxy. In 1998, the stars’ high speeds revealed they orbit an object 4 million times as massive as the Sun. Because Sgr A* packs so much mass into such a small volume, general relativity predicts it must be a supermassive black hole. Reinhard Genzel, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics, independently tracked the stars to reach the same conclusion and shared the Nobel Prize with Ghez.

    Richard Genzel studied back holes at the VLT of the European Southern Observatory.

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo.

    Much of the information comes from a single star, dubbed SO2 by Ghez, which whips around Sgr A* once every 16 years.

    Star S0-2 Andrea Ghez Keck/UCLA Galactic Center Group at SGR A*, the supermassive black hole at the center of the Milky Way.

    Just as the orbit of Mercury around the Sun precesses, so, too, should the orbit of SO2. Ghez and colleagues are now trying to tease out that precession from the extremely complicated data. “We’re right on the cusp,” she says. “We have a signal, but we’re still trying to convince ourselves that it’s real.” (In April 2020, Genzel and colleagues claimed to have seen the precession.)

    If they get a little lucky, Ghez and company hope to look for other anomalies that would probe the nature of the supermassive black hole. Close to the black hole, its spin should modify the precession of a star’s orbit in a way that’s predictable from Kerr’s mathematical description. “If there were stars even closer than the ones they’ve seen—maybe 10 times closer—then you could test whether the Kerr metric is exactly correct,” Will says.

    The star tracking will likely never probe very close to the event horizon of Sgr A*, which could fit within the orbit of Mercury. But EHT, which combines data from 11 radio telescopes or arrays around the world to form, essentially, one big telescope, has offered a closer look at a different supermassive black hole, the 6.5-billion-solar-mass beast in M87.

    The famous image the team released 2 years ago, which resembles a fiery circus hoop, is more complicated than it looks. The bright ring emanates from hot gas, but the dark center is not the black hole itself. Rather it is a “shadow” cast by the black hole as its gravity distorts or “lenses” the light from the gas in front of it. The edge of shadow marks not the event horizon, but rather a distance about 50% farther out where spacetime is distorted just enough so that passing light circles the black hole, neither escaping nor falling into the maw.

    Even so, the image holds clues about the object at its center. The spectrum of the glowing ring could reveal, for example, whether the object has a physical surface rather than an event horizon. Matter crashing onto a surface would shine even brighter than stuff sliding into a black hole, Özel explains. (So far researchers have seen no spectral distortion.) The shadow’s shape can also test the classical picture of a black hole. A spinning black hole’s event horizon should bulge at the equator. However, other effects in general relativity should counteract that effect on the shadow. “Because of a very funky cancellation of squishing in different directions, the shadow still looks circular,” Özel says. “That’s why the shape of the shadow becomes a direct test of the no-hair theorem.”

    Some researchers doubt EHT can image the black hole with enough precision for such tests. Samuel Gralla, a theorist at UA, questions whether EHT is even seeing a black hole shadow or merely viewing the disk of gas swirling around the black hole from the top down, in which case the dark spot is simply the eye of that astrophysical hurricane. But Özel says that even with limited resolution, EHT can contribute significantly to testing general relativity in the conceptual terra incognita around a black hole.

    Gravitational waves, in contrast, convey information straight from the black holes themselves. Churned out when black holes spiral together at half the speed of light, these ripples in spacetime pass unimpeded through ordinary matter. LIGO and Virgo have now detected mergers of black holes with masses ranging from three to 86 solar masses.

    The mergers can probe the black holes in several ways, says Frank Ohme, a gravitational theorist and LIGO member at the Max Planck Institute for Gravitational Physics. Assuming the objects are classical black holes, researchers can calculate from general relativity how the chirplike gravitational wave signal from a merger should speed up, climax in a spike, and then ring down. If the massive partners are actually larger material objects, then as they draw close they should distort each other, altering the peak of the signal. So far, researchers see no alterations, Ohme says.

    The merger produces a perturbed black hole just like the one in Teukolsky’s old thesis, offering another test of general relativity. The final black hole undulates briefly but powerfully, at one main frequency and multiple shorter lived overtones. According to the no-hair theorem, those frequencies and lifetimes only depend on the final black hole’s mass and spin. “If you analyze each mode individually, they all have to point to the same black hole mass and spin or something’s wrong,” Ohme says.

    In September 2019, Teukolsky and colleagues teased out the main vibration and a single overtone from a particularly loud merger. If experimenters can improve the sensitivity of their detectors, Ohme says, they might be able to spot two or three overtones—enough to start to test the no-hair theorem.

    Future instruments may make such tests much easier. The 30-meter optical telescopes being built in Chile and Hawaii should scrutinize the neighborhood of Sgr A* with a resolution roughly 80 times better than current instruments, Ghez says, possibly spying closer stars. Similarly, EHT researchers are adding more radio dishes to their network, which should enable them to image the black hole in M87 more precisely. They’re also trying to image Sgr A*.

    Meanwhile, gravitational wave researchers are already planning the next generation of more sensitive detectors, including the Laser Interferometer Space Antenna (LISA), made up of three satellites flying in formation millions of kilometers apart. To be launched in the 2030s, LISA would be so sensitive that it could spot an ordinary stellar-mass black hole spiraling into a much bigger supermassive black hole in a distant galaxy, says Nicolas Yunes, a theoretical physicist at the University of Illinois, Urbana-Champaign.

    The smaller black hole would serve as a precise probe of the spacetime around the bigger black hole, revealing whether it warps and twists exactly as the Kerr metric dictates. An affirmative result would cement the case that black holes are what general relativity predicts, Yunes says. “But you have to wait for LISA.”

    In the meantime, the sudden observability of black holes has changed the lives of gravitational physicists. Once the domain of thought experiments and elegant but abstract calculations like Teukolsky’s, general relativity and black holes are suddenly the hottest things in fundamental physics, with experts in general relativity feeding vital input to billion-dollar experiments. “I felt this transition very literally myself,” Ohme says. “It was really a small niche community, and with the detection of gravitational waves that all changed.”


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  • richardmitnick 11:24 am on October 29, 2020 Permalink | Reply
    Tags: "Designing new mirror materials for better gravitational-wave detection", , , , , Caltech/MIT Advanced aLigo, , , ,   

    From MIT News: “Designing new mirror materials for better gravitational-wave detection” 

    MIT News

    From MIT News

    October 28, 2020
    Kelso Harper | MIT Kavli Institute

    MIT Kavli Institute for Astrophysics and Space Research.

    Nicholas Demos, a first-generation college graduate and MathWorks Fellow in MIT’s Kavli Institute, is improving our ability to listen to the cosmos.

    1
    Nicholas Demos (left) shows a mirror-testing apparatus to Satoshi Tanioka, a visiting student from Sokendai University (JP).
    Credits: Photo courtesy of the researchers.

    Nicholas Demos, a physics graduate student, didn’t travel a conventional path to MIT. A first-generation college student, Demos didn’t have a clear trajectory in mind when he first attended California State University at Fullerton after high school. “It was kind of the path of least resistance,” Demos says.

    When his father passed away in the middle of his undergraduate studies, Demos left school to run the family business, Novatech Lighting Systems, which makes handheld spotlights. He ran the company for five years, but business didn’t suit him, he says: “The pursuit of money wasn’t motivating at all to me.”

    As soon as his brother graduated and could take over the business, Demos was ready to go back to school — this time with a clearer purpose. He chose to study physics, since he’d always excelled in math and science. Demos was the only student in his high school class to pass the AP calculus exam and even had what he calls a “side hustle” of building and selling computers out of his garage.

    His renewed determination for academics paid off. After his first year back at CSU Fullerton, Demos’ physics professor, Geoffrey Lovelace, asked him to join his lab. The following summer, Demos began researching gravitational waves, just as a more sensitive version of the Laser-Interferometer Gravitational Wave Observatory (LIGO) became operational.

    “The detector was reaching a sensitivity where everyone thought it should work,” says Demos, “Being on the cusp of a big discovery was exciting.”

    On Sept. 14, 2015, a little more than a year after Demos began his research, LIGO detected a gravitational wave for the very first time. It thrilled everyone in the small but growing field, including Demos. The ability to observe gravitational waves provides “a totally different way to look at the universe,” says Demos. “It’s a big step forward for astrophysics; there’s potential for things we haven’t even thought of appearing. A lot of unknown unknowns.”

    When Demos completed his undergraduate degree in 2017, he applied to MIT, hoping to continue working on LIGO. Matthew Evans, the MIT MathWorks Professor of Physics and Demos’ current advisor, says he was immediately impressed with Demos’ work. And according to Evans, Demos’ old advisor told him, “Nick was the best undergraduate he’d ever had.”

    Demos measures mirrors

    Whereas telescopes look for cosmic phenomena, LIGO listens.

    MIT /Caltech Advanced aLigo .

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

    Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    “LIGO is listening for the densest objects in the universe — neutron stars and black holes,” Demos says.

    Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo (IT) came online in August 2018.

    When these massive bodies near each other, they fall into a collapsing orbit, spinning faster and faster, closer and closer, until they collide.

    “What LIGO detects is this chirp — this faster and faster, louder and louder signal — that is like the sound of spacetime vibrating,” Demos says.

    These vibrations, or gravitational waves, travel vast distances through the universe, warping everything — stars, planets, people — in their path. What LIGO does is measure this stretching and squeezing of spacetime. “It’s basically a big, four-kilometer ruler,” Demos says.

    To measure gravitational waves, a LIGO detector has dual four-kilometer vacuum chambers laid in an enormous “L” shape [above]. Scientists split a beam of light and send it to the end of each chamber, where it bounces off of highly reflective mirrors and returns to the corner of the “L.”

    When a gravitational wave ripples through the Earth, it will stretch one arm of LIGO while squashing the other. The light, which has a fixed speed and won’t warp with the rest of the world, then takes a different length of time to travel down each arm. The scientists can measure this difference to detect the wave.

    The challenge is that the ripples caused by gravitational waves are minuscule since, despite appearances, gravity is a very weak force. In terms of the squashing and stretching, “we’re talking about these tiny, fractional changes,” says Demos, “roughly one-thousandth the size of a proton.”

    This means that everything in the LIGO experiment must be extremely precise and very still. Otherwise, the gravitational wave signals will be lost in a sea of noise. Unfortunately, some sources of noise are harder to eliminate than others.

    “The surface of the mirror is made up of atoms, and these atoms are jiggling about,” Demos says. “If you’re trying to measure something that’s smaller than a proton, that’s a problem, because your ruler is jiggling about on both ends.”

    The noise from the movement of atoms, also called thermal noise, is nearly unavoidable — the motion only stops at the unreachable temperature of absolute zero. However, some materials have less of this thermal noise than others.

    Demos’ job is to design and test new mirror materials to find those with the lowest thermal noise. In fact, he is one of the few people in the world able to test these samples. Matthew Evans and Research Scientist Slawomir Gras have developed the only apparatus able to quickly test full mirror samples, as opposed to just a single layer or a few layers of the materials used to coat the mirrors.

    “Any coating that LIGO wants to use will first be characterized by our experiment,” Demos says.

    The Evans lab is in the process of upgrading their setup to measure thermal noise across the surface of a sample, as opposed to only at a single point.

    “This is a job which is really at the heart of progress in gravitational wave detection,” Evans adds. “Nick’s persistent determination to get things done has really made a big difference for us.”

    Demos makes math work with MATLAB

    In September, Demos was one of a select group of students in the School of Science to receive a $70,000 fellowship from MathWorks, a software company that produces mathematical computing programs like MATLAB and Simulink.

    “The MathWorks Fellowship is a big honor,” says Demos, “It’s a huge relief financially because I don’t have to worry, my lab doesn’t have to worry, and I’ll be able to really pursue this.”

    It’s particularly appropriate for Demos to win this fellowship, as he frequently uses MATLAB in his research. “He’s gone through all of our analysis software in MATLAB and really refactored that code from the ground up,” says Evans. He adds that Demos is very deserving of this award, but he’s not worried about the recognition going to Demos’ head.

    “There’s a certain humility in his approach to things, which is not something you always find.”
    Share this news article on:

    See the full article here .


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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 11:08 am on September 25, 2020 Permalink | Reply
    Tags: "Physicists Argue That Black Holes From the Big Bang Could Be the Dark Matter", , , , , Caltech/MIT Advanced aLigo, , , Unseen “primordial” black holes might be the hidden dark matter-a new series of studies has shown how the theory can work.   

    From Quanta Magazine: “Physicists Argue That Black Holes From the Big Bang Could Be the Dark Matter” 

    From Quanta Magazine

    September 23, 2020
    Joshua Sokol

    1
    Primordial black holes would cluster in distinct clumps throughout the universe. Relatively large black holes would be surrounded by much smaller ones. Olena Shmahalo/Quanta Magazine.

    It was an old idea of Stephen Hawking’s: Unseen “primordial” black holes might be the hidden dark matter. It fell out of favor for decades, but a new series of studies has shown how the theory can work.

    Black holes are like sharks. Elegant, simple, scarier in the popular imagination than they deserve, and possibly lurking in deep, dark places all around us.

    Their very blackness makes it hard to estimate how many black holes inhabit the cosmos and how big they are. So it was a genuine surprise when the first gravitational waves thrummed through detectors at the Laser Interferometer Gravitational-Wave Observatory (LIGO) in September 2015.

    MIT /Caltech Advanced aLigo .

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

    Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy.

    Previously, the largest star-size black holes had topped out at around 20 times the mass of the sun. These new ones were about 30 solar masses each — not inconceivable, but odd. Moreover, once LIGO turned on and immediately started hearing these sorts of objects merge with each other, astrophysicists realized that there must be more black holes lurking out there than they had thought. Maybe a lot more.

    The discovery of these strange specimens breathed new life into an old idea — one that had, in recent years, been relegated to the fringe. We know that dying stars can make black holes. But perhaps black holes were also born during the Big Bang itself. A hidden population of such “primordial” black holes could conceivably constitute dark matter, a hidden thumb on the cosmic scale. After all, no dark matter particle has shown itself, despite decades of searching. What if the ingredients we really needed — black holes — were under our noses the whole time?

    “Yes, it was a crazy idea,” said Marc Kamionkowski, a cosmologist at Johns Hopkins University whose group came out with one of the many eye-catching papers [Physical Review Letters] that explored the possibility in 2016. “But it wasn’t necessarily crazier than anything else.”

    2
    Samuel Velasco/Quanta Magazine; source: LIGO -Virgo/Frank Elavsky, Aaron Geller/Northwestern.

    Alas, the flirtation with primordial black holes soured in 2017, after a paper by Yacine Ali-Haïmoud, an astrophysicist at New York University who had previously been on the optimistic Kamionkowski team, examined how this type of black hole should affect LIGO’s detection rate. He calculated [The merger rate of primordial-black-hole binaries” in Physical Review D] that if the baby universe spawned enough black holes to account for dark matter, then over time, these black holes would settle into binary pairs, orbit each other closer and closer, and merge at rates thousands of times higher than what LIGO observes. He urged other researchers to continue to investigate the idea using alternate approaches. But many lost hope. The argument was so damning that Kamionkowski said it quenched his own interest in the hypothesis.

    Now, however, following a flurry of recent papers, the primordial black hole idea appears to have come back to life. In one of the latest, published last week in the Journal of Cosmology and Astroparticle Physics, Karsten Jedamzik, a cosmologist at the University of Montpellier, showed how a large population of primordial black holes could result in collisions that perfectly match what LIGO observes. “If his results are correct — and it seems to be a careful calculation he’s done — that would put the last nail in the coffin of our own calculation,” said Ali-Haïmoud, who has continued to play with the primordial black hole idea in subsequent papers too. “It would mean that in fact they could be all the dark matter.”

    “It’s exciting,” said Christian Byrnes, a cosmologist at the University of Sussex who helped inspire some of Jedamzik’s arguments. “He’s gone further than anyone has gone before.”

    The original idea dates back to the 1970s with the work of Stephen Hawking and Bernard Carr. Hawking and Carr reasoned that in the universe’s first fractions of a second, small fluctuations in its density could have endowed lucky — or unlucky — regions with too much mass. Each of these regions would collapse into a black hole. The size of the black hole would be dictated by the region’s horizon — the parcel of space around any point reachable at the speed of light. Any matter within the horizon would feel the black hole’s gravity and fall in. Hawking’s rough calculations showed that if the black holes were bigger than small asteroids, they could plausibly still be lurking in the universe today.

    More progress came in the 1990s. By then, theorists also had the theory of cosmic inflation, which holds that the universe experienced a burst of extreme expansion right after the Big Bang. Inflation could explain where the initial density fluctuations would have come from.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lamda Cold Dark Matter Accerated Expansion of The universe http scinotions.com the-cosmic-inflation-suggests-the-existence-of-parallel-universes
    Alex Mittelmann, Coldcreation


    Alan Guth’s notes:

    Alan Guth’s original notes on inflation

    On top of those density fluctuations, physicists also considered a key transition that would coax along the collapse.

    When the universe was new, all of its matter and energy seethed in an unthinkably hot plasma. After the first hundred-thousandth of a second or so, the universe cooled a little, and the plasma’s loose quarks and gluons could bind together into heavier particles. With some of the lightning-fast particles now straitjacketed together, the pressure dropped. That might have helped more regions collapse into black holes.

    But back in the 1990s, nobody understood the physics of a fluid of quarks and gluons well enough to make precise predictions about how this transition would affect black hole production. Theorists couldn’t say how massive primordial black holes should be, or how many to expect.

    Moreover, cosmologists didn’t really seem to need primordial black holes. Astronomical surveys scanned patches of sky hoping to find a sea of dense, dark objects like black holes floating on the outskirts of the Milky Way, but they didn’t find many. Instead, most cosmologists came to believe that dark matter was made of ultra-shy particles called WIMPs. And hopes simmered that either purpose-built WIMP detectors or the upcoming Large Hadron Collider would soon find hard evidence of them.

    With the dark matter problem about to wrap itself up with a bow and no observations suggesting otherwise, primordial black holes became an academic backwater. “One senior cosmologist kind of ridiculed me for working on that,” said Jedamzik, who traces his own interest back to the 1990s. “So I stopped that, because I needed to have a permanent position.”

    Of course, no WIMPs have been found in the decades since then, nor any new particles (save the long-predicted Higgs boson). Dark matter remains dark.

    Yet much more is known today about the environment that could have spawned primordial black holes. Physicists can now calculate how pressure and density would have evolved from the quark-gluon plasma at the beginning of the universe. “It took the community really decades to work this out,” said Byrnes. With that information in hand, theorists such as Byrnes and Juan García-Bellido at the Autonomous University of Madrid have spent the last few years publishing studies [Primordial black holes, dark matter and hot-spot electroweak baryogenesis at the quark-hadron epoch] predicting that the early universe could have spawned not just one size of black hole, but a range of them.

    First, the quarks and gluons were glued together into protons and neutrons. That caused a pressure drop and could have spawned one set of primordial black holes. As the universe kept cooling, particles such as pions formed, creating another pressure plunge and possible black hole burst.

    Between these epochs, space itself expanded. The first black holes could suck in about one solar mass of material from the horizon around themselves.

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project.

    The second round could grab perhaps about 30 solar masses’ worth — just like the strange objects first seen by LIGO. “Gravitational waves came to our rescue,” said García-Bellido.

    Within weeks of the first gravitational wave announcement from LIGO in 2016, the primordial black hole hypothesis roared back to life. But the following year, Ali-Haïmoud came out with his argument that primordial black holes would be colliding far too often, which gave proponents a major hurdle to overcome.

    Jedamzik took up the challenge. During a long vacation in Costa Rica, he went after Ali-Haïmoud’s argument. Ali-Haïmoud had done his work analytically, through equations. But when Jedamzik created numerical simulations of the same problem, he found a twist.

    Primordial black holes would indeed form binaries. But Jedamzik concluded that in a universe teeming with black holes, a third black hole would often approach the initial pair and change places with one of them. This process would repeat again and again.

    Over time, this swinging from partner to partner would leave binary black holes with almost circular orbits. These partners would be incredibly slow to collide. Even a huge population of primordial black holes would merge so infrequently that the entire hypothesis would still fit within LIGO’s observed merger rate.

    4
    One arm of the LIGO detector located in Livingston, Louisiana. Credit: William Widmer for Quanta Magazine.

    He posted his work online this June [Primordial Black Hole Dark Matter and the LIGO/Virgo observations], fielding questions from outside experts like Ali-Haïmoud himself. “It was very important to convince the community, as much as you can, that you are not just saying some nonsense,” said Jedamzik, using a more forceful term than “nonsense.”

    He also built on work that predicted that primordial black holes would sit in dark clusters about as large in diameter as the distance between the sun and the nearest star. Each of these clusters might contain around a thousand black holes crammed together. The 30-solar-mass behemoths would sit at the center; the more common littler ones would fill in the rest of the space. These clusters would lurk everywhere astronomers think dark matter is. As with stars in a galaxy or planets circling the sun, each black hole’s orbital motion would keep it from devouring another — except during those uncommon mergers.

    In a second paper [Evidence for primordial black hole dark matter from LIGO/Virgo merger rates], Jedamzik calculated exactly how uncommon these mergers should be. He made the calculations for the big black holes that LIGO has observed, and for the smaller ones, which it has not. (Small black holes would produce faint, high-pitched signals and would have to be close by to be detected.) “I was, of course, stunned to see that one after the other I got the rate right,” he said.

    Advocates of the primordial black hole hypothesis still have a lot of convincing to do. Most physicists still believe that dark matter is made of some kind of elementary particle, one that’s devilishly hard to detect. Moreover, the LIGO black holes aren’t too different from what we would expect if they came from ordinary stars. “It sort of fills a hole in the theory that isn’t actually there,” said Carl Rodriguez, an astrophysicist at Carnegie Mellon University. “There are things that are weird about some of the LIGO sources, but we can explain everything that we’ve seen so far through normal stellar evolutionary process.”

    Selma de Mink, an astrophysicist at Harvard University who has sketched out theories for how stars alone can produce the heavy black hole binaries seen by LIGO, is more blunt: “I think astronomers can laugh a bit about it.”

    Finding just one black hole of sub-solar mass — which should be common, according to the primordial black hole scenario, and which can’t form from stars — would transform this entire debate. And with every subsequent observing run, LIGO has increased its sensitivity, allowing it to eventually either find such small black holes or set strict limits on how many can exist. “This is not one of these stories like string theory, where in a decade or three decades we might still be discussing if it’s correct,” Byrnes said.

    In the meantime, other astrophysicists are probing different aspects of the theory. For example, perhaps the strongest constraints on primordial black holes come from microlensing searches — those same surveys that began in the 1990s. In these efforts, astronomers monitor bright but distant sources, waiting to see if a dark object passes in front of them. These searches have long ruled out an evenly dispersed population of small black holes.

    But if primordial black holes exist at a range of masses, and if they’re packed into dense, massive clusters, those results could be less significant than researchers thought, García-Bellido said.

    Upcoming observations might eventually settle that question, too. The European Space Agency has recently agreed to contribute a key extra feature to NASA’s upcoming Nancy Grace Roman Space Telescope, one that would allow it to do groundbreaking microlensing studies.

    NASA/Nancy Grace Roman Space Telescope.

    The addition came at the behest of Günther Hasinger, ESA’s science director, who made the case that primordial black holes could explain multiple mysteries. To Hasinger, the idea is appealing because it doesn’t invoke new particles or new physics theories. It just repurposes old elements.

    “I believe maybe some of the puzzles which are still out there could actually solve themselves,” he said, “when you look with different eyes.”

    See the full article here .


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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.

     
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