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  • richardmitnick 4:54 pm on May 24, 2016 Permalink | Reply
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    From Goddard: “NASA Scientist Suggests Possible Link Between Primordial Black Holes and Dark Matter” 

    NASA Goddard Banner

    NASA Goddard Space Flight Center

    May 24, 2016
    Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Maryland

    Dark matter is a mysterious substance composing most of the material universe, now widely thought to be some form of massive exotic particle. An intriguing alternative view is that dark matter is made of black holes formed during the first second of our universe’s existence, known as primordial black holes. Now a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, suggests that this interpretation aligns with our knowledge of cosmic infrared and X-ray background glows and may explain the unexpectedly high masses of merging black holes detected last year.

    “This study is an effort to bring together a broad set of ideas and observations to test how well they fit, and the fit is surprisingly good,” said Alexander Kashlinsky, an astrophysicist at NASA Goddard. “If this is correct, then all galaxies, including our own, are embedded within a vast sphere of black holes each about 30 times the sun’s mass.”

    In 2005, Kashlinsky led a team of astronomers using NASA’s Spitzer Space Telescope to explore the background glow of infrared light in one part of the sky.

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    The researchers reported excessive patchiness in the glow and concluded it was likely caused by the aggregate light of the first sources to illuminate the universe more than 13 billion years ago. Follow-up studies confirmed that this cosmic infrared background (CIB) showed similar unexpected structure in other parts of the sky.

    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA)
    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA)

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    After masking out all known stars, galaxies and artifacts and enhancing what’s left, an irregular background glow appears. This is the cosmic infrared background (CIB); lighter colors indicate brighter areas.

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    This image from NASA’s Spitzer Space Telescope shows an infrared view of a sky area in the constellation Ursa Major.

    The CIB glow is more irregular than can be explained by distant unresolved galaxies, and this excess structure is thought to be light emitted when the universe was less than a billion years old. Scientists say it likely originated from the first luminous objects to form in the universe, which includes both the first stars and black holes.

    In 2013, another study compared how the cosmic X-ray background (CXB) detected by NASA’s Chandra X-ray Observatory compared to the CIB in the same area of the sky.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The first stars emitted mainly optical and ultraviolet light, which today is stretched into the infrared by the expansion of space, so they should not contribute significantly to the CXB.

    Yet the irregular glow of low-energy X-rays in the CXB matched the patchiness of the CIB quite well. The only object we know of that can be sufficiently luminous across this wide an energy range is a black hole. The research team concluded that primordial black holes must have been abundant among the earliest stars, making up at least about one out of every five of the sources contributing to the CIB.

    The nature of dark matter remains one of the most important unresolved issues in astrophysics. Scientists currently favor theoretical models that explain dark matter as an exotic massive particle, but so far searches have failed to turn up evidence these hypothetical particles actually exist. NASA is currently investigating this issue as part of its Alpha Magnetic Spectrometer and Fermi Gamma-ray Space Telescope missions.

    AMS-02 Bloc
    NASA/AMS02 device
    AMS02

    NASA/Fermi Telescope
    NASA/Fermi Telescope

    “These studies are providing increasingly sensitive results, slowly shrinking the box of parameters where dark matter particles can hide,” Kashlinsky said. “The failure to find them has led to renewed interest in studying how well primordial black holes — black holes formed in the universe’s first fraction of a second — could work as dark matter.”

    Physicists have outlined* several ways in which the hot, rapidly expanding universe could produce primordial black holes in the first thousandths of a second after the Big Bang. The older the universe is when these mechanisms take hold, the larger the black holes can be. And because the window for creating them lasts only a tiny fraction of the first second, scientists expect primordial black holes would exhibit a narrow range of masses.

    On Sept. 14, gravitational waves produced by a pair of merging black holes 1.3 billion light-years away were captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana.

    Caltech/MIT  Advanced Ligo Hanford, WA, USA installation
    Caltech/MIT Advanced Ligo Hanford, WA, USA installation

    Caltech/MIT Advanced aLigo detector in Livingston, Louisiana
    Caltech/MIT Advanced aLigo detector in Livingston, LA, USA

    This event marked the first-ever detection of gravitational waves as well as the first direct detection of black holes.


    Primordial black holes, if they exist, could be similar to the merging black holes detected by the LIGO team in 2014. This computer simulation shows in slow motion what this merger would have looked like up close. The ring around the black holes, called an Einstein ring, arises from all the stars in a small region directly behind the holes whose light is distorted by gravitational lensing. The gravitational waves detected by LIGO are not shown in this video, although their effects can be seen in the Einstein ring. Gravitational waves traveling out behind the black holes disturb stellar images comprising the Einstein ring, causing them to slosh around in the ring even long after the merger is complete. Gravitational waves traveling in other directions cause weaker, shorter-lived sloshing everywhere outside the Einstein ring. If played back in real time, the movie would last about a third of a second.
    Credits: SXS Lensing
    Access mp4 video here .

    The signal provided LIGO scientists with information about the masses of the individual black holes, which were 29 and 36 times the sun’s mass, plus or minus about four solar masses. These values were both unexpectedly large and surprisingly similar.

    In his new paper**, published May 24 in The Astrophysical Journal Letters, Kashlinsky analyzes what might have happened if dark matter consisted of a population of black holes similar to those detected by LIGO. The black holes distort the distribution of mass in the early universe, adding a small fluctuation that has consequences hundreds of millions of years later, when the first stars begin to form.

    For much of the universe’s first 500 million years, normal matter remained too hot to coalesce into the first stars. Dark matter was unaffected by the high temperature because, whatever its nature, it primarily interacts through gravity. Aggregating by mutual attraction, dark matter first collapsed into clumps called minihaloes, which provided a gravitational seed enabling normal matter to accumulate. Hot gas collapsed toward the minihaloes, resulting in pockets of gas dense enough to further collapse on their own into the first stars. Kashlinsky shows that if black holes play the part of dark matter, this process occurs more rapidly and easily produces the lumpiness of the CIB detected in Spitzer data even if only a small fraction of minihaloes manage to produce stars.

    As cosmic gas fell into the minihaloes, their constituent black holes would naturally capture some of it too. Matter falling toward a black hole heats up and ultimately produces X-rays. Together, infrared light from the first stars and X-rays from gas falling into dark matter black holes can account for the observed agreement between the patchiness of the CIB and the CXB.

    Occasionally, some primordial black holes will pass close enough to be gravitationally captured into binary systems. The black holes in each of these binaries will, over eons, emit gravitational radiation, lose orbital energy and spiral inward, ultimately merging into a larger black hole like the event LIGO observed.

    “Future LIGO observing runs will tell us much more about the universe’s population of black holes, and it won’t be long before we’ll know if the scenario I outline is either supported or ruled out,” Kashlinsky said.

    Kashlinsky leads science team centered at Goddard that is participating in the European Space Agency’s Euclid mission, which is currently scheduled to launch in 2020.

    ESA/Euclid spacecraft
    ESA/Euclid spacecraft

    The project, named LIBRAE, will enable the observatory to probe source populations in the CIB with high precision and determine what portion was produced by black holes.

    *Science paper:
    Primordial Black Holes – Recent Developments

    **Science paper:
    LIGO GRAVITATIONAL WAVE DETECTION, PRIMORDIAL BLACK HOLES, AND THE NEAR-IR COSMIC INFRARED BACKGROUND ANISOTROPIES

    See the full article here.

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

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

    NASA Goddard Campus
    NASA/Goddard Campus
    NASA

     
  • richardmitnick 3:06 pm on May 24, 2016 Permalink | Reply
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    From Hubble: “Hubble finds clues to the birth of supermassive black holes” 

    NASA Hubble Banner

    NASA Hubble Telescope

    Hubble

    24 May 2016
    At ESA/Hubble
    Fabio Pacucci
    Scuola Normale Superiore
    Pisa, Italy
    Email: fabio.pacucci@sns.it

    Andrea Ferrara
    Scuola Normale Superiore
    Pisa, Italy
    Email: andrea.ferrara@sns.it

    Andrea Grazian
    National Institute for Astrophysics
    Rome, Italy
    Email: grazian@oa-roma.inaf.it

    Mathias Jäger
    ESA/Hubble, Public Information Officer
    Garching bei München, Germany
    Tel: +49 176 62397500
    Email: mjaeger@partner.eso.org

    At NASA/Chandra
    Media contacts:
    Felicia Chou / Sean Potter
    Headquarters, Washington
    202-358-0257 / 1536
    felicia.chou@nasa.gov / sean.potter@nasa.gov

    Megan Watzke
    Chandra X-ray Center, Cambridge, Mass.
    617-496-7998
    mwatzke@cfa.harvard.edu

    1

    Astrophysicists have taken a major step forward in understanding how supermassive black holes formed. Using data from Hubble and two other space telescopes, Italian researchers have found the best evidence yet for the seeds that ultimately grow into these cosmic giants.

    For years astronomers have debated how the earliest generation of supermassive black holes formed very quickly, relatively speaking, after the Big Bang. Now, an Italian team has identified two objects in the early Universe that seem to be the origin of these early supermassive black holes. The two objects represent the most promising black hole seed candidates found so far [1].

    The group used computer models and applied a new analysis method to data from the NASA Chandra X-ray Observatory, the NASA/ESA Hubble Space Telescope, and the NASA Spitzer Space Telescope to find and identify the two objects. Both of these newly discovered black hole seed candidates are seen less than a billion years after the Big Bang and have an initial mass of about 100 000 times the Sun.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    “Our discovery, if confirmed, would explain how these monster black holes were born,” said Fabio Pacucci, lead author of the study, of Scuola Normale Superiore in Pisa, Italy.

    This new result helps to explain why we see supermassive black holes less than one billion years after the Big Bang.

    There are two main theories to explain the formation of supermassive black holes in the early Universe. One assumes that the seeds grow out of black holes with a mass about ten to a hundred times greater than our Sun, as expected for the collapse of a massive star. The black hole seeds then grew through mergers with other small black holes and by pulling in gas from their surroundings. However, they would have to grow at an unusually high rate to reach the mass of supermassive black holes already discovered in the billion years young Universe.

    The new findings support another scenario where at least some very massive black hole seeds with 100 000 times the mass of the Sun formed directly when a massive cloud of gas collapses [2]. In this case the growth of the black holes would be jump started, and would proceed more quickly.

    “There is a lot of controversy over which path these black holes take,” said co-author Andrea Ferrara also of Scuola Normale Superiore. “Our work suggests we are converging on one answer, where black holes start big and grow at the normal rate, rather than starting small and growing at a very fast rate.”

    Andrea Grazian, a co-author from the National Institute for Astrophysics in Italy explains: “Black hole seeds are extremely hard to find and confirming their detection is very difficult. However, we think our research has uncovered the two best candidates so far.”

    Even though both black hole seed candidates match the theoretical predictions, further observations are needed to confirm their true nature. To fully distinguish between the two formation theories, it will also be necessary to find more candidates.

    These results* will appear in the June 21st issue of the Monthly Notices of the Royal Astronomical Society and is available online. The authors of the paper are Fabio Pacucci (SNS, Italy), Andrea Ferrara (SNS), Andrea Grazian (INAF), Fabrizio Fiore (INAF), Emaneule Giallongo (INAF), and Simonetta Puccetti (ASI Science Data Center).

    The team plans to conduct follow-up observations in X-rays and in the infrared range to check whether the two objects have more of the properties expected for black hole seeds. Upcoming observatories, like the NASA/ESA/CSA James Webb Space Telescope and the European Extremely Large Telescope will certainly mark a breakthrough in this field, by detecting even smaller and more distant black holes.

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile
    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile

    Notes

    [1] Supermassive black holes contain millions or even billions of times the mass of the Sun. In the modern Universe they can be found in the centre of nearly all large galaxies, including the Milky Way.

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

    The supermassive black hole in the centre of the Milky Way has a mass of four million solar masses. The two black hole seed candidates would also be the progenitors of two of the modern supermassive black holes.

    [2] Black hole seeds created through the collapse of a massive cloud of gas bypass any other intermediate phases such as the formation and subsequent destruction of a massive star.

    The team of scientists in this study consists of Fabio Pacucci (Scuola Normale Superiore, Italy), Andrea Ferrara (Scuola Normale Superiore, Italy), Andrea Grazian (INAF, Italy), Fabrizio Fiore (INAF, Italy), Emanuele Giallongo (INAF, Italy), Simonetta Puccetti (ASDC-ASI, Italy)

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

    NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate in Washington, D.C. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

    *Science paper:
    First Identification of Direct Collapse Black Hole Candidates in the Early Universe in CANDELS/GOODS-S

    See the full article here .

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    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 10:11 am on May 23, 2016 Permalink | Reply
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    From Daily Galaxy: “”Attempt No Journey There” –Swarm of 10,000 Black Holes and Neutron Stars Orbit Milky Way’s Supermassive Black Hole” 

    Daily Galaxy
    The Daily Galaxy

    1
    No image caption, no image credit

    May 22, 2016

    “The giant black holes in the cores of galaxies, a million to 20 billion times heavier than the Sun, therefore, cannot have been born in the death of a star. They must have formed in some other way, perhaps by the agglomeration of many smaller black holes; perhaps by the collapse of massive clouds of gas.” ― Kip S. Thorne, The Science of Interstellar.

    “The Center of our Milky Way Galaxy is a place of extremes,” says Mark Morris, an expert on The Galactic Center at UCLA. “For every star in our nighttime sky, for example, there would be a million for someone looking up from a planet near the Galactic center.”

    Thinking about a far-future visit to our galaxy’s central zone, brings to mind Arthur C. Clark’s admonition about a visit to Jupiter’s ocean moon, Europa –“All These Worlds are Yours –Except Europa Attempt No Landing There.” In addition to the extreme star density, a swarm of 10,000 or more black holes may be orbiting the Milky Way’s supermassive black hole, according to observations from NASA’s Chandra X-ray Observatory in 2015.

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

    This would represent the highest concentration of black holes anywhere in the Galaxy. These relatively small, stellar-mass black holes, along with neutron stars, appear to have migrated into the Galactic Center over the course of several billion years. Could this migration be the prelude to feeding our supermassive black hole suggested by Caltech’s Kip Thorne?

    The discovery was made as part of Chandra’s ongoing program of monitoring the region around Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, reported by by Michael Muno of the University of California, Los Angeles (UCLA) at a 2015 meeting of the American Astronomical Society.

    Among the thousands of X-ray sources detected within 70 light years of Sgr A*, Muno and his colleagues searched for those most likely to be active black holes and neutron stars by selecting only the brightest sources that also exhibited large variations in their X-ray output. These characteristics identify black holes and neutron stars that are in binary star systems and are pulling matter from nearby companion stars. Of the seven sources that met these criteria, four are within three light years of Sgr A*.

    “Although the region around Sgr A* is crowded with stars, we expected that there was only a 20 percent chance that we would find even one X-ray binary within a three-light-year radius,” said Muno. “The observed high concentration of these sources implies that a huge number of black holes and neutron stars have gathered in the center of the Galaxy.”

    Mark Morris, also of UCLA and a coauthor on the present work, had predicted a decade ago that a process called dynamical friction would cause stellar black holes to sink toward the center of the Galaxy. Black holes are formed as remnants of the explosions of massive stars and have masses of about 10 suns. As black holes orbit the center of the Galaxy at a distance of several light years, they pull on surrounding stars, which pull back on the black holes.

    2
    Unidentified. No image credit.

    3

    The images above are part of a Chandra program that monitors a region around the Milky Way’s supermassive black hole, Sagittarius A* (Sgr A*). Four bright, variable X-ray sources (circles) were discovered within 3 light years of Sgr A* (the bright source just above Source C). The lower panel illustrates the strong variability of one of these sources. This variability, which is present in all the sources, is indicative of an X-ray binary system where a black hole or neutron star is pulling matter from a nearby companion star.

    “Stars are packed quite close together in the center zone,” says Morris. “Then, there’s that supermassive black hole that is sitting in there, relatively quiet for now, but occasionally producing a dramatic outpouring of energy. The UCLA Galactic center group been use the Keck Telescopes in Hawaii to follow its activity for the last 17 years, watching not only the fluctuating emission from the black hole, but also watching the stars around it as they rapidly orbit the black hole.”

    Morris had predicted a decade ago that a process called dynamical friction would cause stellar black holes to sink toward the center of the Galaxy. Black holes are formed as remnants of the explosions of massive stars and have masses of about 10 suns. As black holes orbit the center of the Galaxy at a distance of several light years, they pull on surrounding stars, which pull back on the black holes. The net effect is that black holes spiral inward, and the low-mass stars move out. From the estimated number of stars and black holes in the Galactic Center region, dynamical friction is expected to produce a dense swarm of 20,000 black holes within three light years of Sgr A*. A similar effect is at work for neutron stars, but to a lesser extent because they have a lower mass.

    Once black holes are concentrated near Sgr A*, they will have numerous close encounters with normal stars there, some of which are in binary star systems. The intense gravity of a black hole can induce an ordinary star to “change partners” and pair up with the black hole while ejecting its companion. This process and a similar one for neutron stars are expected to produce several hundreds of black hole and neutron star binary systems.

    The black holes and neutron stars in the cluster are expected to gradually be swallowed by the supermassive black hole, Sgr A*, at a rate of about one every million years. At this rate, about 10,000 black holes and neutron stars would have been captured in a few billion years, adding about 3 percent to the mass of the central supermassive black hole, which is currently estimated to contain the mass of 3.7 million suns.

    In the meantime, the acceleration of low-mass stars by black holes will eject low-mass stars from the central region. This expulsion will reduce the likelihood that normal stars will be captured by the central supermassive black hole. This may explain why the central regions of some galaxies, including the Milky Way, are fairly quiet even though they contain a supermassive black hole.

    See the full article here .

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  • richardmitnick 3:58 pm on May 7, 2016 Permalink | Reply
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    From Ethan Siegel: “Ask Ethan: How Does Dark Matter Interact With Black Holes?” 

    Starts with a Bang

    May 7, 2016
    Ethan Siegel

    Black Hole Image credit NASA JPL-Caltech.
    Black Hole Image credit: NASA/JPL-Caltech

    Black holes are some of the most extreme objects in the Universe: a concentration of mass so great that it collapses, under General Relativity, into a singularity at its center. Atoms, nuclei, and even fundamental particles themselves are crushed down to an arbitrarily small thickness in our three-dimensional space. At the same time, everything that falls into it is doomed to never escape, but simply to add to its gravitational pull. What does that mean for dark matter? Our Patreon supporter kilobug wants to know:

    How does dark matter interact with black holes? Does it get sucked into the singularity like normal matter, contributing to the mass of the black hole? If so, when the black hole evaporates through Hawking radiation, what happens to [it]?

    This is a great question, and it all starts with what black holes actually are.

    Here on Earth, if you want to send something into space, you need to overcome the Earth’s gravitational pull. For our planet, what we call “escape velocity” is somewhere around 25,000 mph (or 11.2 km/s), which we can achieve with powerful rocket launches. If we were instead on the surface of the Sun, the escape velocity would be much greater: about 55 times as great, or 617.5 km/s. When our Sun dies, it will contract down to a white dwarf, of about 50% the Sun’s current mass but only the physical size of Earth. In this case, its escape velocity will be about 4570 km/s, or about 1.5% the speed of light.

    1
    Sirius A and B, a normal (Sun-like) star and a white dwarf star. Even though the white dwarf is much lower in mass, its tiny, Earth-like size ensures its escape velocity is many times larger. Image credit: NASA, ESA and G. Bacon (STScI)

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    This is important, because as you concentrate more and more mass into a particular region of space, the speed required to escape this object gets closer and closer to the speed of light. And once your escape velocity at the object’s surface reaches or exceeds [?] the speed of light, it isn’t just that light can’t get out, it’s required that — at least as we understand matter, energy, space and time today — everything within that object collapse down to a singularity. The reason is simple: all the fundamental forces, including the forces that hold atoms, protons, or even quarks together, can move no faster than the speed of light. So if you’re at any point away from a central singularity and you’re trying to hold a more distant object up against gravitational collapse, you can’t do it; collapse is inevitable. And all you need to crest past this limit in the first place is a star more massive than about 20-40 times the mass of our Sun.

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    Dying star. Associate Professor Orsola De Marco from Sydney’s Macquarie University.http://www.zmescience.com/space/dying-star-nebulae-26072011/

    When it runs out of fuel in its core, the center will implode under its own gravity, creating a catastrophic supernovae, blowing off and destroying the outer layers but leaving a black hole at the center. These “stellar mass” black holes, somewhere in the neighborhood of 10 solar masses, will grow over time, consuming any matter or energy that dares to venture too close to it. Even if you move at the speed of light when you fall in, you’ll never get out again. Due to the extreme curvature of space inside, you’ll inevitably encounter the singularity at the center. When that happens, all you do is add to the energy of the black hole.

    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital
    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital

    From the outside, we can’t tell whether a black hole was initially made up of protons and electrons, neutrons, dark matter or even antimatter. There are — as far as we can tell — only three properties that we can observe about a black hole from outside of it: its mass, its electric charge and its angular momentum, which is a measure of how fast it’s spinning. Dark matter, as far as we know, has no electric charge, nor does it have any of the other quantum numbers (color charge, baryon number, lepton number, lepton family number, etc.) that may or may not be conserved or destroyed as pertains to the black hole information paradox.

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    Illustration credit: ESA, retrieved via http://chandra.harvard.edu/resources/illustrations/blackholes2.html.

    Because of how black holes are formed (from the explosions of supermassive stars), when they’re first formed, black holes are pretty much 100% normal (baryonic) matter, and just about 0% dark matter. Remember that dark matter interacts only gravitationally, unlike normal matter, which interacts via the gravitational, weak, electromagnetic and strong forces. Yes, there’s perhaps five times as much dark matter total in large galaxies and clusters as there is normal matter, but that’s summed up over the entire huge halo.

    Dark matter halo  Image credit: Virgo consortium / A. Amblard / ESA
    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    In a typical galaxy, that dark matter halo extends for a few million light years, spherically, in all directions, while the normal matter is concentrated in a disk that’s just 0.01% the dark matter’s volume.

    Black holes tend to form in the innards of the galaxy, where the normal matter totally dominates over dark matter. Consider just the region of space where we’re located: around our Sun. If we drew a sphere that was 100 AU in radius (where one AU is the distance of the Earth from the Sun) around our Solar System, we’d enclose all the planets, moons, asteroids and pretty much the entire Kuiper belt…

    Kuiper Belt. Minor Planet Center
    Kuiper Belt. Minor Planet Center

    … but the baryonic mass — the normal matter — of what would be inside our sphere would be dominated by our Sun, and would weigh about 2 × 10^30 kg. On the other hand, the total amount of dark matter in that same sphere? Only about 1 × 10^19 kg, or just 0.0000000005% the mass of the normal matter in that same region, or about the mass of a modest asteroid the size of Juno, approximately 200 km across.

    Our Solar system, NASA/Chandra
    Our Solar system, NASA/Chandra

    Over time, dark matter and normal matter both will collide with this black hole, getting absorbed and adding to its mass. The vast majority of black hole mass growth will come from normal matter and not dark matter, although at some point, many quadrillion years into the future, the rate of black hole decay will finally surpass the rate of black hole growth. The Hawking radiation process results in the emission of particles and photons from outside the black hole’s event horizon, conserving all the energy, charge and angular momentum from the black hole’s insides. This process may take anywhere from 10^67 years (for a solar mass black hole) to 10^100 years (for the most massive multi-billion solar mass black holes), but eventually what comes out is a mix of everything that’s possible.

    This means that some dark matter will come out of black holes, but that’s expected to be completely independent of whether a substantial amount of dark matter went into the black hole in the first place. All a black hole has memory of, once things have fallen in, is a small set of quantum numbers, and the amount of dark matter that went into it isn’t one of them. What comes out isn’t going to be the same as what you put in!

    5
    Image credit: E. Siegel, on the quantum origin of Hawking Radiation.

    So at the end of the day, dark matter is just another food source for black holes, and not a very good one at that. Even worse: it’s not even an interesting source of food. What black hole “sees” is no different than shining a flashlight into a black hole and having your photons absorbed until, via E=mc^2, you’ve put in as much energy as there is mass in the dark matter that fell in. No other types of charge exist in dark matter, and other than the angular momentum from falling in off-center (which applies to photons, too), there’s no other effect on black holes at all, either going in or coming out.

    See the full article here .

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

     
  • richardmitnick 11:13 am on May 5, 2016 Permalink | Reply
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    From ALMA: “ALMA Measures Mass of Black Hole with Extreme Precision” 

    ALMA Array

    ALMA

    05 May 2016

    Nicolás Lira T.
    Education and Public Outreach Coordinator
    Joint ALMA Observatory
    Santiago, Chile
    Tel: +56 2 2467 6519
    Cell: +56 9 9445 7726
    Email: nicolas.lira@alma.cl

    Charles E. Blue
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    Tel: +1 434 296 0314
    Cell: +1 202 236 6324
    E-mail: cblue@nrao.edu

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    Education and Public Outreach Officer, NAOJ Chile
    Observatory
Tokyo, Japan

    Tel: +81 422 34 3630

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    Public Information Officer, ESO

    Garching bei München, Germany

    Tel: +49 89 3200 6655

    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    1
    Combined image of NGC 1332 shows the central disk of gas surrounding the supermassive black hole at the center of the galaxy. New ALMA observations traced the motion of the disk, providing remarkably precise measurements of the black hole’s mass: 660 million times the mass of our Sun. The main image is from the Carnegie-Irvine Galaxy Survey. The box in the upper left is from the Hubble Space Telescope and shows the galaxy’s central region in infrared light and the dusty disk appears as a dark silhouette. The ALMA image, upper right box, shows the rotation of the disk, enabling astronomers to calculate its mass. The red region in the ALMA image represents emission that has been redshifted by gas rotating away from us; the blue represents blue-shifted gas rotating toward us. The range of colors represent rotational speeds up to 500 kilometers per second. Credit: A. Barth (UC Irvine), ALMA (NRAO/ESO/NAOJ); NASA/ESA Hubble; Carnegie-Irvine Galaxy Survey.

    3
    DSS image of lenticular galaxy NGC 1332 and part of elliptical galaxy NGC 1331. Celestial Atlas.

    Supermassive black holes, some weighing millions to billions of times the mass of the Sun, dominate the centers of their host galaxies. To determine the actual mass of a supermassive black hole, astronomers must measure the strength of its gravitational pull on the stars and clouds of gas that swarm around it.

    Using the Atacama Large Millimeter/submillimeter Array (ALMA), a team of astronomers has delved remarkably deep into the heart of a nearby elliptical galaxy to study the motion of a disk of cold interstellar gas encircling the supermassive black hole at its center. These observations provide one of the most accurate mass measurements to date for a black hole outside of our Galaxy, helping set the scale for these cosmic behemoths.

    To obtain this result, Aaron Barth, an astronomer at the University of California, Irvine (UCI), and lead author on a paper published* in the Astrophysical Journal Letters, and his team used ALMA to measure the speed of carbon monoxide gas in orbit around the black hole at the center of NGC 1332, a massive elliptical galaxy approximately 73 million light-years from Earth in the direction of the southern constellation Eridanus.

    “Measuring the mass of a black hole accurately is very challenging, even with the most powerful telescopes on Earth or in space,” Barth said. “ALMA has the revolutionary ability to observe disks of cold gas around supermassive black holes at small enough scales that we can clearly distinguish the black hole’s influence on the disk’s rotational speed.”

    The ALMA observations reveal details of the disk’s structure on the order of 16 light-years across. They also measure the disk’s rotation well within the estimated 80 light-year radius of the black hole’s “sphere of influence” – the region where the black hole’s gravity is dominant.

    Near the disk’s center, ALMA observed the gas traveling at more than 500 kilometers per second. By comparing these data with simulations, the astronomers calculated that the black hole at the center of NGC 1332 has a mass 660 million times greater than our Sun, plus or minus ten percent. This is about 150 times the mass of the black hole at the center of the Milky Way, yet still comparatively modest relative to the largest black holes known to exist, which can be many billions of solar masses.

    ALMA’s close-in observations were essential, the researchers note, to avoid confounding the black hole measurement with the gravitational influence of other material – stars, clouds of interstellar gas, and dark matter – that comprises most of the galaxy’s overall mass.

    “This black hole, though individually massive, accounts for less one percent of the mass of all the stars in the galaxy,” noted Barth. “Most of a galaxy’s mass is in the form of dark matter and stars, and on the scale of an entire galaxy, even a giant black hole is just a tiny speck in the center. The key to detecting the influence of the black hole is to observe orbital motion on such small scales that the black hole’s gravitational pull is the dominant force.” This observation is the first demonstration of this capability for ALMA.

    Astronomers use various techniques to measure the mass of black holes. All of them, however, rely on tracing the motion of objects as close to the black hole as possible. In the Milky Way, powerful ground-based telescopes using adaptive optics can image individual stars near the galactic center and precisely track their trajectories over time. Though remarkably accurate, this technique is feasible only within our own Galaxy; other galaxies are too distant to distinguish the motion of individual stars.

    To make similar measurements in other galaxies, astronomers either examine the aggregate motion of stars in a galaxy’s central region, or trace the motion of gas disks and mega-masers — natural cosmic radio sources.

    Previous studies of NGC 1332 with ground- and space-based telescopes gave wildly different estimates for the mass of this black hole, ranging from 500 million to 1.5 billion times the mass of the Sun.

    The new ALMA data confirm that the lower estimates are more accurate.

    Crucially, the new ALMA observations have higher resolution than any of the past observations. ALMA also detects the emission from the densest, coldest component of the disk, which is in a remarkably orderly circular motion around the black hole.

    Many past measurements made with optical telescopes, including the Hubble Space Telescope, focused on the emission from the hot, ionized gas orbiting in the central region of a galaxy. Ionized-gas disks tend to be much more turbulent than cold disks, which leads to lower precision when measuring a black hole’s mass.

    “ALMA can map out the rotation of gas disks in galaxy centers with even sharper resolution than the Hubble Space Telescope,” noted UCI graduate student Benjamin Boizelle, a co-author on the study. “This observation demonstrates a technique that can be applied to many other galaxies to measure the masses of supermassive black holes to remarkable precision.”

    Additional information

    These results were published* in the Astrophysical Journal Letters as Measurement of the black hole mass in NGC 1332 from ALMA observations at 0.044 arcsecond resolution, by Aaron Barth et al.

    The team is composed of Aaron Barth (University of California, Irvine), Benjamin D. Boizelle (University of California, Irvine), Jeremy Darling (University of Colorado, Boulder), Andrew J. Baker (Rutgers, the State University of New Jersey, Piscataway), David A. Buote (University of California, Irvine), Luis Ho (Kavli Institute of Astronomy and Astrophysics, Peking University, China), and Jonelle L. Walsh (Texas A&M University, College Station).

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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  • richardmitnick 7:06 pm on April 28, 2016 Permalink | Reply
    Tags: , , Black Holes,   

    From Nautilus: “Where Nature Hides the Darkest Mystery of All” 

    Nautilus

    Nautilus

    April 28, 2016
    Matthew Francis

    No known object in existence has as clear a division between “inside” and “outside” as a black hole. We live and see the outside, and no probe will bring us information about the inside. We can send radio messages or robotic spacecraft, but once they cross over into a black hole’s interior, we’ll never get back those emissaries … or any information about what happened to them.

    The boundary of a black hole is its event horizon. It’s not a surface in the usual sense—there’s no physical barrier—but it’s very much a real thing. Outside the horizon, an object can escape the black hole’s gravitational pull if it’s moving sufficiently fast; inside, it would need to move faster than light-speed, something forbidden by the laws of nature.

    In a meaningful sense, a black hole is its event horizon, since we can’t observe anything inside it by any method. The interior is nature’s biggest secret, enshrouded by a barrier that lets everything in but nothing out.

    1
    Simulating Space: A computer simulation of a gas cloud passing near the supermassive black hole at the center of the Milky Way, and the gravitational effects on the cloud. ESO/MPE/Marc Schartmann

    To make black holes even more enigmatic, they are also perfectly featureless, according to general relativity, our best explanation of how gravity works. They may be born from situations as different as the deaths of stars and the gravitational collapse of huge amounts of gas in the early universe, but the result is the same. Even the chemical composition of what gets sucked into and forms it is irrelevant. The only properties a black hole exhibits to the wider cosmos are its mass and how fast it’s rotating.

    This result is puckishly known as the “no-hair theorem”: Whatever is going on in the interior, no “hair” sticks out of the event horizon. (The name was coined by prominent physicist John Archibald Wheeler, obviously not a man sensitive about a receding hairline.) That theorem presents a challenging conundrum: We don’t know whether a black hole actually deletes its autobiography, “forgetting” its past and its progenitor’s composition, or preserves it somehow in a way we don’t know yet. If that information is destroyed, it’s a violation of one of the principles of quantum mechanics; if it’s preserved, it requires a theory beyond general relativity.

    The interior of a black hole isn’t merely an inaccessible region of the cosmos. It’s a laboratory for the most extreme physics: the strongest gravity and the most intense of quantum processes. For that reason, physicists are interested in understanding what goes on inside, even while they are frustrated by the lack of direct experiments or observations that could test their ideas.

    We can’t penetrate the bald event horizon, but that doesn’t mean we know nothing about a black hole’s interior. We’re pretty sure black holes don’t contain a portal to another region of space (a wormhole) or another reality, whatever sci-fi may have told us. Most physicists are also reasonably certain that a full description of the interior of black holes will require quantum gravity, a theory unifying quantum physics and general relativity—or possibly a modified version of our current model of gravity. The full structure of such a theory is unknown, but researchers have some thumbnail sketches about what it might look like.

    One hybrid approach was put together by Yakov Borisovich Zel’dovich, Jacob Bekenstein, and especially Stephen Hawking. Without a quantum theory of gravity, they used particle physics in combination with general relativity to show that the event horizon has a non-zero temperature and therefore glows, albeit very faintly. This glow is known as Hawking radiation; it arises when partnered particles—one electron and one positron, pairs of photons, etc.—are created in the intense gravitational field. One particle falls into the black hole, while the other escapes.

    Since the energy from the black hole was the source of the newly created particles’ mass (via E = mc2), the black hole’s mass shrinks slightly with every escaped particle. Unfortunately, the event horizon temperature is low for black holes like the ones we see, so Hawking radiation is correspondingly much fainter than other sources of light. However, if very low-mass black holes exist, they would shine brightly by Hawking radiation, and decay relatively quickly, evaporating away to nothing. Watching such a black hole vanish might help answer the question of whether information is truly lost or just hidden from us by the event horizon.

    Interestingly, Hawking himself thinks the problem has been solved, at least in principle: Black holes preserve the information they swallow, much as a hologram preserves information about three dimensions even though they are two-dimensional pictures. His hypothesis, based on an idea in string theory, doesn’t yet work in our four-dimensional cosmos (three spatial dimensions plus time), but rather for an abstract, higher-dimensional universe. As a result, not everyone is convinced by Hawking’s demonstration, even if they agree that black holes don’t forget their origins.

    Hawking radiation presumably consists of all sorts of things, including exotic particles like dark matter and gravitons, which we’ve never seen in the lab. That’s an intriguing notion, though again nature cruelly interferes with our best efforts to study it, by making tiny black holes rare or perhaps nonexistent. We might be able to see Hawking radiation from a larger black hole, but only if it’s not actively feeding on matter and if the hole is very close by. (Another option would be to create a tiny black hole in the lab, but without some new, exotic kind of physics, the necessary energy is beyond our reach.)

    The nearest known black hole to Earth, which carries the highly memorable name V404 Cygni, is about 8,000 light-years away. While that’s a mere hair’s breadth in cosmic terms, it’s far enough that we can’t study it up close. (For comparison, Voyager 1—the farthest human-built probe—is a little over 17 light-hours away at the time of writing.) The closest supermassive black hole (one that exceeds 100,000 times the mass of the sun) is even farther away: 26,000 light-years. That’s the monster at the center of the Milky Way, known as Sagittarius A* (pronounced “A star”).

    2
    V404 CYGNI, DSS Ultracam

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

    We see black holes like V404 Cygni by the matter surrounding them: Material stripped off companion stars, for example, heats up as it orbits the black hole, emitting strong X-ray and radio radiation. Thanks to high-resolution observations made last year, astronomers have measured swirling gas at very close orbits to the giant black hole in the galaxy M87. And the dance of stars and plasma near Sagittarius A* reveals the presence of the black hole that helps keep our galaxy together.

    With continued improvements, we’ll be able to get an even better view of black holes, drawing ever closer to the event horizon. Yet nature still hides the mystery of what lies inside a black hole, perhaps forever.

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 12:48 pm on April 26, 2016 Permalink | Reply
    Tags: , Black Holes,   

    From Science Alert: “Physicists have created a ‘black hole’ in the lab that could finally prove Hawking radiation exists” 

    ScienceAlert

    Science Alert

    26 APR 2016
    BEC CREW

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

    1
    Alain r/Wikimedia

    Will Stephen Hawking get his Nobel prize?

    Some 42 years ago, renowned theoretical physicist Stephen Hawking proposed that not everything that comes in contact with a black hole succumbs to its unfathomable nothingness. Tiny particles of light (photons) are sometimes ejected back out, robbing the black hole of an infinitesimal amount of energy, and this gradual loss of mass over time means every black hole eventually evaporates out of existence.

    Known as Hawking radiation, these escaping particles help us make sense of one of the greatest enigmas in the known Universe, but after more than four decades, no one’s been able to actually prove they exist, and Hawking’s proposal remained firmly in hypothesis territory.

    But all that could be about to change, with two independent groups of researchers reporting that they’ve found evidence to back up Hawking’s claims, and it could see one of the greatest living physicists finally win a Nobel Prize.

    So let’s go back to 1974, when all of this began. Hawking had gotten into an argument with Princeton University graduate student, Jacob Bekenstein, who suggested in his PhD thesis that a black hole’s entropy – the ‘disorder’ of a system, related to its volume, energy, pressure, and temperature – was proportional to the area of its event horizon.

    As Dennis Overbye explains for The New York Times, this was a problem, because according to the accepted understanding of physical laws at the time – including Hawking’s own work – the entropy and the volume of a black hole could never decrease.

    Hawking investigated the claims, and soon enough, realised that he had been proven wrong. “[D]r Hawking did a prodigious calculation including quantum theory, the strange rules that govern the subatomic world, and was shocked to find particles coming away from the black hole, indicating that it was not so black after all,” Overbye writes.

    Hawking proposed that the Universe is filled with ‘virtual particles’ that, according to what we know about how quantum mechanics works, blink in and out of existence and annihilate each other as soon as they come in contact – except if they happen to appear on either side of a black hole’s event horizon. Basically, one particle gets swallowed up by the black hole, and the other radiates away into space.

    The existence of Hawking radiation has answered a lot of questions about how black holes actually work, but in the process, raised a bunch of problems that physicists are still trying to reconcile.

    “No result in theoretical physics has been more fundamental or influential than his discovery that black holes have entropy proportional to their surface area,” says Lee Smolin, a theoretical physicist from the Perimeter Institute for Theoretical Physics in Canada.

    While Bekenstein received the Wolf Prize in 2012 and the American Physical Society’s Einstein prize in 2015 for his work, which The New York Times says are often precursors to the Nobel Prize, neither scientist has been awarded the most prestigious prize in science for the discovery. Bekenstein passed away last year, but Hawking is now closer than ever to seeing his hypothesis proven.

    The problem? Remember when I said the escaping photons were stealing an infinitesimal amount of energy from a black hole every time they escaped? Well, unfortunately for Hawking, this radiation is so delicate, it’s practically impossible to detect it from thousands of light-years away.

    But physicist Jeff Steinhauer from Technion University in Haifa, Israel, thinks he’s come up with a solution – if we can’t detect Hawking radiation in actual black holes thousands of light-years away from our best instruments, why not bring the black holes to our best instruments?

    As Oliver Moody reports for The Times, Steinhauer has managed to created a lab-sized ‘black hole’ made from sound, and when he kicked it into gear, he witnessed particles steal energy from its fringes.

    Reporting his experiment in a paper* posted to the physics pre-press website, arXiv.org, Steinhauer says he cooled helium to just above absolute zero, then churned it up so fast, it formed a ‘barrier’ through which sound should not be able to pass.

    “Steinhauer said he had found signs that phonons, the very small packets of energy that make up sound waves, were leaking out of his sonic black hole just as Hawking’s equations predict they should,” Moody reports.

    To be clear, the results of this experiment have not yet been peer-reviewed – that’s the point of putting everything up for the public to see on arXiv.org. They’re now being mulled over by physicists around the world, and they’re already proving controversial, but worthy of further investigation.

    “The experiments are beautiful,” physicist Silke Weinfurtner from the University of Nottingham in the UK, who is running his own Earth-based experiments to try and detect Hawking radiation, told The Telegraph. “Jeff has done an amazing job, but some of the claims he makes are open to debate. This is worth discussing.”

    Meanwhile, a paper published** in Physical Review Letters last month has found another way to strengthen the case for Hawking radiation. Physicists Chris Adami and Kamil Bradler from the University of Ottawa describe a new technique that allows them to follow a black hole’s life over time.

    That’s exciting stuff, because it means that whatever information or matter that passes over the event horizon doesn’t ‘disappear’ but is slowly leaking back out during the later stages of the black hole’s evaporation.

    “To perform this calculation, we had to guess how a black hole interacts with the Hawking radiation field that surrounds it,” Adami said in a press release. “This is because there currently is no theory of quantum gravity that could suggest such an interaction. However, it appears we made a well-educated guess because our model is equivalent to Hawking’s theory in the limit of fixed, unchanging black holes.”

    Both results will now need to be confirmed, but they suggest that we’re inching closer to figuring out a solution for how we can confirm or disprove the existence of Hawking radiation, and that’s good news for its namesake.

    As Moody points out, Peter Higgs, who predicted the existence of the Higgs boson, had to wait 49 years for his Nobel prize, we’ll have to wait and see if Hawking ends up with his own.

    *Science paper:
    Observation of thermal Hawking radiation and its entanglement in an analogue black hole

    **Science Paper:
    One-Shot Decoupling and Page Curves from a Dynamical Model for Black Hole Evaporation

    See the full article here .

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  • richardmitnick 12:58 pm on April 14, 2016 Permalink | Reply
    Tags: , , Black Holes,   

    From phys.org: “The hot problem of black hole firewalls” 

    physdotorg
    phys.org

    April 14, 2016
    Ross Lockwood

    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital
    Black hole and its accretion disk. Image credit NASA Dana Berry SkyWorks Digital

    For the last four years, physicists studying the mathematical underpinnings of black holes have been wrestling with a strange idea: that black holes contain a region known as a “firewall,” which utterly annihilates matter that dares to cross its boundaries. However, a new paper titled Naked Black Hole Firewalls*, co-authored by University of Alberta physics professor Don N. Page, aims to attack the fundamental tenets that give rise to this strange idea—with something much stranger.

    “The putative black hole firewall is one of the hottest problems in physics today, and we hope that our paper makes a significant contribution to the field,” says Page. “As part of the University of Alberta community, I’ve been privileged to be able to interact with many others in this field around the world.”

    Page’s contributors include Pisin Chen of the National Taiwan University and Stanford University, Yen Chin Ong of the Nordic Institute for Theoretical Physics (Nordita), Misao Sasaki of Kyoto University and Dong-han Yeom of the National Taiwan University.

    The classic picture of a black hole comes directly from Einstein’s theory of general relativity: a massive object warps the fabric of spacetime and, given sufficient material, this region of spacetime becomes so steep that not even light has sufficient speed to escape. Because no light can escape, these objects became known as black holes, entering our cultural consciousness as the universe’s most terrifying garbage disposals. A hapless space traveller entering the black hole’s event horizon, according to this model, would be completely destroyed inside the black hole.

    Despite their apparent simplicity, however, black holes have been devilishly difficult to describe, and in the 1970s, physicist Stephen Hawking proposed that some particles could in fact escape from a black hole through a process involving the creation of entangled particles, in a theory now known as Hawking radiation. Since then, the field of black hole physics has been a wellspring of interesting phenomena, requiring the mathematics of both quantum theory and general relativity for a complete description.

    In the intervening four decades, an outstanding problem—the black hole information paradox—has continued to stymie physicists as a direct result of introducing the mathematics of quantum theory into the mix. “At first, most scientists working on Einstein’s theory of gravity thought Hawking’s original suggestion was right, that information is lost when black holes form and evaporate,” says Page, who wrote the first paper objecting to Hawking’s suggestion. “Now most, though not all, gravitational physicists, including Hawking himself, believe that information is not lost. However, it is still mysterious how the information is preserved in detail.”

    In quantum mechanics, the two principles of quantum determinism and reversibility suggest that information must always be preserved. But since material falling into a black hole—along with the information describing that material—are apparently annihilated sometime after they cross the event horizon, physicists have been left scratching their heads about this seeming inconsistency.

    The paradox itself arises due to Hawking radiation, which demonstrates that matter can be emitted from a black hole, but initially it appeared that no information about the matter that once fell into the black hole is carried away. In 2012, a group of physicists studying this paradox found that three basic assumptions involved in this paradox cannot all be consistent.

    Namely, principles of unitarity and local quantum field theory contradicted the assumption of “no-drama”—meaning that nothing unusual should happen when an object falls through the event horizon. Instead, they proposed that the most conservative solution to this contradiction is that there would indeed be “drama” at the surface of the black hole in the form of a “firewall” that would destroy an infalling object. This seems rather surprising, because the curvature is negligibly small at the event horizon of a sufficiently large black hole, where general relativity should hold and one would expect nothing special when crossing the horizon.

    “So-called firewalls, or high-energy density regions that we would otherwise think of as the surface of the black hole, would destroy anything falling in,” explains collaborator Pisin Chen at the National Taiwan University.

    The putative position of the firewall is something that didn’t sit well with the authors of the paper, who began work on this project at a workshop at the Yukawa Institute for Theoretical Physics in Kyoto, Japan. Since the firewall was proposed to be hidden behind the event horizon, an observer travelling past the gently curved event horizon of a large black hole, hoping to glimpse its interior, would instead be instantly incinerated the moment they passed behind the veil. Attacking the fundamental tenets used to create the firewall, the authors demonstrate that this region of quantum-mechanical destruction can strangely migrate to a region outside of the black hole due to the quantum fluctuations of the Hawking radiation, allowing an observer a full-frontal view of a black hole’s “naked firewall.”

    “If a firewall exists, not only would an infalling object be destroyed by it, but the destruction could be visible, even from the outside,” says Misao Sasaki, a contributor from Kyoto University.

    Page emphasizes that such a “naked firewall” outside of the event horizon is problematic. If a firewall actually exists, the authors argue that it wouldn’t simply be confined to a region within the black hole, but its destructive power could reach beyond the limits of the event horizon, into a region of space that could be observed. This makes the notion of firewalls less conservative than previously thought, and suggests putting more effort into finding a better solution to the firewall paradox.

    Science paper
    *Naked Black Hole Firewalls.
    Science team:
    Pisin Chen, 1,2; Yen Chin Ong, 3 y; Don N. Page, 4, z; Misao Sasaki, 5, x; and Dong-han Yeom, 1

    Affiliations
    1 Leung Center for Cosmology and Particle Astrophysics,
    National Taiwan University, Taipei 10617, Taiwan
    2 Kavli Institute for Particle Astrophysics and Cosmology,
    SLAC National Accelerator Laboratory,
    Stanford University, CA 94305, U.S.A.
    3 Nordita, KTH Royal Institute of Technology & Stockholm University,
    Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden
    4 Theoretical Physics Institute, University of Alberta,
    Edmonton, Alberta T6G 2E1, Canada
    5 Yukawa Institute for Theoretical Physics,
    Kyoto University, Kyoto 606-8502, Japan

    See the full article here .

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    About Phys.org in 100 Words

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

     
  • richardmitnick 9:38 am on April 14, 2016 Permalink | Reply
    Tags: , , Black Holes, ,   

    From Science Alert: “Astronomers have discovered a region in space where black holes have mysteriously aligned” 

    ScienceAlert

    Science Alert

    12 APR 2016
    BEC CREW

    1

    What the hell’s going on out there?

    There’s a region in the distant Universe where a handful of supermassive black holes have mysteriously aligned, and as a result, they’re spewing out incredibly powerful radio jets in the same direction. This is the first time astronomers have seen such a phenomenon, and they say it could be the result of fluctuations of primordial mass that appeared in the early Universe.

    “Since these black holes don’t know about each other, or have any way of exchanging information or influencing each other directly over such vast scales, this spin alignment must have occurred during the formation of the galaxies in the early Universe,” explains one of the team, Andrew Russ Taylor, director of South Africa’s Institute for Data Intensive Astronomy.

    As with many discoveries that happen in outer space, no one was expecting to find a region where supermassive black holes had mysteriously managed to sync up their spins.

    Taylor and his team were actually on the hunt for the faintest radio sources in the Universe, using data from the Giant Metrewave Radio Telescope (GMRT) in India – one of the largest and most sensitive radio telescope arrays in the world.

    Giant Metrewave Radio Telescope near Pune in India
    Giant Metrewave Radio Telescope near Pune in India

    The GMRT had just completed a three-year deep radio imaging survey, detecting radio waves spewed forth by black holes in a distant region of the Universe called ELAIS, which encompasses several galaxies.

    By looking at the direction these radio waves were coming from, the researchers figured out that within ELAIS-N1, the supermassive black holes at the centre of each of these galaxies were all spinning in the same direction. But how?

    Taylor and his colleagues suggest that the black holes are too far apart to have influenced each other’s alignment in their current positions in space, so whatever forced them into the same spin must happened very early on in the formation of the Universe.

    “[T]he alignment of the black holes is probably caused by an overall spin in the structure of this region of space, triggered by fluctuations of primordial matter in the early Universe, way before galaxies even formed,” Yasmin Tayag reports for Inverse.

    But if we accept that, then something even greater must have given rise to the fluctuations of primordial matter that caused these supermassive black holes to align. In other words, what caused the fluctuations that forced these black holes into the same spin?

    It’s not yet clear, and a large-scale spin distribution has not been predicted by our current understanding of the physics that govern the Universe, but the researchers suggest that it could be anything from incredibly strong cosmic magnetic fields – possibly associated with exotic particles such as axions – to something called cosmic strings, which are theoretical fault lines in the Universe that exist between different regions of space.

    “This is not obviously expected based on our current understanding of cosmology. It’s a bizarre finding,” astronomer Romeel Dave from the University of Western Cape in South Africa, who was not involved in the discovery, said in a press statement.

    We’re going to need much more sensitive telescopes to figure that out, and with the South African MeerKAT radio telescope and the Square Kilometre Array (SKA) – the world’s most powerful radio telescope and one of the biggest scientific instruments ever devised – currently under construction, we might not have to wait too long.

    SKA Meerkat telescope
    SKA Meerkat telescope

    “[We really need MeerKAT to make the very sensitive maps, over a very large area and with great detail, that will be necessary to differentiate between possible explanations,” says Taylor. “It opens up a whole new research area for these instruments, which will probe as deeply into the and as far back as we can go – it’s going to be an exciting time to be an astronomer.”

    The discovery has been reported* in the Monthly Notices of the Royal Astronomical Society.

    *Science paper:
    Alignments of radio galaxies in deep radio imaging of ELAIS N1

    Science team:
    A. R. Taylor 1,2,★ and P. Jagannathan 1,3

    Affiliations:
    1 Department of Astronomy, University of Cape Town, Rondebosch 7701, South Africa
    2 Department of Physic and Astronomy, University of the Western Cape, Bellville 7535, South Africa
    3 National Radio Astronomy Observatory, Socorro, NM, USA

    See the full article here .

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  • richardmitnick 4:50 pm on April 8, 2016 Permalink | Reply
    Tags: , Black Holes, ,   

    From New Scientist: “Physics adventures down the superfluid supersonic black hole” 

    NewScientist

    New Scientist

    9 April 2016
    Anil Ananthaswamy

    1
    What happens to the stuff a black hole sucks in? Jan Kornstaedt/Gallerystock

    IMAGINE lying in a giant bathtub when someone pulls the plug. Sliding towards a watery exit from this world, it gets worse. The fluid gathers pace to supersonic speed and you realise no one can even hear you scream. Your sounds are transported with you down the drain, lost to the bathtub for all time.

    It is the stuff of surrealist nightmares – and a pretty fair description of what happens to an atom or a photon of light as it crosses a black hole’s event horizon. Black holes famously devour anything that comes too close: light, matter, information. In doing so, they cause some almighty headaches for our best theories of physical reality.

    Or do they? Although we are pretty certain black holes exist, we’ve never observed one directly, let alone got up close and personal. That’s where the bathtub analogy is now coming into serious play. Get fully to grips with it, and we could have a new way not just to fathom black holes, but also to crack some of cosmology’s other toughest nuts – from why the expansion of the universe is accelerating to how it all began.

    There’s a catch, naturally. To make the analogy real, we can’t use any old water from the tap. It takes a fluid so extreme and bizarre that it was fabricated for the first time just 20 years ago, and only exists within a whisker of absolute zero, the lowest temperature there is. With that magic ingredient, you can begin to make a superfluid sonic black hole.

    Black holes are the most mysterious of the many predictions made by general relativity, Einstein’s theory of gravity that he formulated just over a century ago. General relativity is a peerless guide to the workings of gravity, but puts gravity at odds with the other known forces of nature. Unlike them, gravity is not caused by the exchange of quantum particles; instead, massive bodies bend space and time around them, creating dents in the fabric of the universe that dictate how other bodies move.

    The world according to general relativity contains some shady spectres – invisible dark matter to explain why galaxies whirl at the speeds they do, and dark energy to explain why the expansion of the universe is accelerating. The theory also fails completely when you wind the universe back to its first instants and the big bang. Here, it predicts a seemingly nonsensical “singularity” of infinite temperature and density.

    Still, black holes take the biscuit. We now think these impossibly dense scrunchings of mass exist across the cosmos – where massive stars have collapsed in on themselves, and at the heart of galaxies including our own.

    For all their heft, however, black holes seem strangely tenuous, at least in theory. In 1974, physicist Stephen Hawking used quantum rules to show that all black holes must eventually evaporate, apparently destroying any information they might have swallowed, a physical no-no.

    According to quantum physics, space-time is a roiling broth of particles and their antiparticles that pop up spontaneously in pairs, disappearing again almost instantaneously. But when such a pair pops up at the edge of a black hole’s event horizon – the point beyond which nothing can escape its gravity – sometimes one will have the energy to whizz away, while the other falls in. By the law of conservation of energy, this second particle must have negative energy, causing the black hole to slowly lose its oomph and evaporate. The signal this is happening is a faint stream of escaping partner particles – Hawking radiation.

    In theory at least, Hawking radiation has a temperature: the smaller the black hole, the warmer it is. For a black hole 30 times the mass of our sun, it is a titchy nanokelvin or so, impossible to measure in the chaotic surroundings of an astrophysical black hole. Hopes were high that the Large Hadron Collider at CERN near Geneva, Switzerland, might produce mini black holes with measurable Hawking radiation – but not a peep.

    CERN/LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    CERN/LHC

    “This is a pity, because if they had, I would have got a Nobel prize,” Hawking said in a BBC lecture this February.

    2
    Bose-Einstein condensates arise when supercooled gases of atoms all enter the same quantum state. Pascal Goetgheluck/Science Photo Library

    Wind back to 1981, however, and physicist William Unruh of the University of British Columbia in Vancouver, Canada, was thinking of ways to study Hawking radiation. It led him to some strange parallels between the “metric” – a mathematical construction in general relativity that expresses the geometry of space-time – and equations used to describe superfluid flow.

    Unruh showed that the equations governing such flow at supersonic speed mimicked the metric of space-time around a black hole. This implied a superfluid could create a black hole that would trap “phonons” of sound, just as an astrophysical black hole traps photons of light. It’s the surrealist nightmare, with an added twist. Just as with an astrophysical black hole, quantum fluctuations would make a sonic black hole emit Hawking radiation – but made of phonons, not photons.

    Unruh realised this could be just the thing to test Hawking’s idea. Prove the radiation exists in one situation, and the mathematical mirror provides a pretty good indication that it does in the other.

    He was rather ahead of the times. Although the first superfluid state was created in liquid helium in the late 1930s, for a sonic black hole the fluid had to be flowing faster than the speed of sound in that fluid – in superfluid helium, that’s hundreds of metres a second. Experimental verification of Unruh’s idea would have to wait.

    Then, in 1995, came a Nobel-prizewinning development: the creation of the first Bose-Einstein condensates (BECs). This is an entirely different state of matter beyond solid, liquid and gas, made up of collections of atoms cooled down to temperatures so low, sometimes a few nanokelvin above absolute zero, that the individual atoms lose their identity. They occupy the same quantum state, and behave and flow as one.

    Sonic event horizon

    Creating this extreme, bizarre form of superfluid was an experimental tour de force, and came with an important detail as far as the black hole story was concerned: in a BEC, the speed of sound is just millimetres a second. Sonic black holes suddenly looked feasible.

    Iacopo Carusotto, a theorist at the BEC Center in Trento, Italy, was initially a sceptic. But returning from holiday in 2005, he found himself sitting next to a college friend on a train who turned out to be a gravitational physicist, and the two got talking shop. The friend introduced Carusotto to Roberto Balbinot, an expert on general relativity at the University of Bologna. These two started to build computer models of sonic black holes that took into account factors such as how the speed of sound varies according to how a fluid is moving, its temperature, the wavelength of the phonons and so on.

    Carusotto still has the first image spewed out by the simulation in 2008 hanging on the wall in his office. “I jumped off my chair,” he says. It shows that as a Bose-Einstein condensate starts flowing at supersonic speeds, a sonic event horizon forms and phonons of Hawking radiation spontaneously appear. “To see it so precisely in agreement with theory was a great surprise, and a great success,” says Carusotto.

    Jeff Steinhauer, an atomic physicist at the Technion-Israel Institute of Technology in Haifa, was the man who could make the analogy an experimental reality. He had developed some crucial tools: a way of measuring a condensate’s temperature to an accuracy of a nanokelvin, and complex systems of adjustable magnetic fields to stop condensates sagging and being disrupted under the effect of real gravity. By 2009, he was able to use lasers to accelerate a long, thin stretch of condensate to supersonic speed. The result was the first sonic black hole with an event horizon (Physical Review Letters*, vol 105, p 240401).

    Measuring individual phonons to verify the existence of Hawking radiation proved more tricky. In 2014, Steinhauer reached a halfway house by accelerating a thin condensate stream to supersonic speed and then allowing it to slow again. This created the equivalent of two event horizons – a black-hole horizon from which no sound could escape, and a “white-hole” horizon into which no sound could enter. In such a situation, Hawking phonons produced by the black hole bounce between the two horizons, producing more and more Hawking radiation in a similar way to how light is amplified in a laser.

    3
    Bose-Einstein condensates may hold the answer. National Institute of Syandards and ethnology/Science Photo Library

    And amplified radiation is certainly what Steinhauer saw. “It was very exciting to suddenly see this effect,” he says. “It was very gratifying to think that the physics Hawking predicted was creating it.” The question raised by Carusotto and others since is how to tell for certain whether the initial phonon was created by spontaneous, random quantum fluctuation rather than some classical process. Final confirmation could be coming soon: Steinhauer currently has a paper** under peer review in which he reports seeing unadorned Hawking radiation from a single sonic horizon (arxiv.org/abs/1510.00621).

    Steinhauer himself wouldn’t discuss this work further, but theorist Stefano Liberati of the International School for Advanced Studies in Trieste, Italy, is excited. “If this result is confirmed, it’s definitely a major breakthrough,” he says. “It would be the first experimental detection of Hawking radiation.”

    Whether it’s enough for Hawking to get his Nobel prize remains to be seen, but Liberati thinks this work is just the beginning. Not only might sonic black holes illuminate further mysteries of the real thing (see “What are black holes made of?“), but get superfluids flowing in different ways and you can create other space-time geometries that equate to other cosmological problems. One is the exponential expansion of the universe in the period known as inflation, thought to have occurred immediately after the big bang. Current cosmological theories predict that during this phase, the quantum fluctuations of space-time also got stretched, eventually giving rise to the particles we see everywhere today. We can’t test this idea directly, but Liberati and his colleagues have shown how a similar situation implemented using a condensate should give rise to phonons. “You should be able to reproduce the salient features of cosmological particle creation,” he says.

    One way of doing this involves using lasers or magnetic fields to suddenly compress a condensate, thus changing the speed of sound within it. This creates an analogy to the change in light’s travel time between two points in space as the universe expands. In 2012, Christoph Westbrook and his colleagues at the Charles Fabry Laboratory at the University of Paris-Sud in France did just that and saw indirect effects of phonon creation – although the experimental temperature of 200 nanokelvin was still too high to rule out thermal fluctuations as the source.

    Liberati suggests that a similar analogy could provide clues to another huge cosmological conundrum, dark energy. The peculiar problem of dark energy is not so much that it exists. General relativity allows for a “cosmological constant” that represents the energy of empty space and whose effect would be to expand space ever faster, just as dark energy is thought to do. But calculating the value of this constant from observations gives a number 10120 times smaller than the value you get from quantum field theory.

    Again, Bose-Einstein condensates could hold the answer. In a condensate, not all the atoms that you cool down end up in the lowest-energy condensate state: you never get a perfect condensate. What’s more, these stragglers “backreact” with the condensate, an interaction that appears in the equations in a similar way to the cosmological constant.

    “The superfluid analogy might provide clues to the cosmic conundrum of dark energy“

    To Liberati, this is suggestive of the real nature of dark energy, and space-time itself. What if the fabric of the universe, and hence gravity, emerge from some as-yet-unknown “atoms” of space-time, just as a superfluid state emerges from normal atoms when they are cooled? If some of these atoms are left over and do not form the basis of space-time, then their backreaction with those that do could reduce the value of the cosmological constant to match what astronomers find.

    In this view, the equations of general relativity might just be a high-level picture that emerges from a more fundamental description. In fluid dynamics, the set of equations known as Euler’s equations similarly describes the flow as a whole, but not the molecular interactions that underlie it. “It’s teaching you a very important lesson,” says Liberati. “If gravity is emergent, the only way you can calculate the cosmological constant is by knowing the fundamental system from which gravity emerges.”

    The quest for a more fundamental picture of gravity is central to the search for a “theory of everything” that will finally unite all the forces of nature, gravity included. So far, convincing answers have been thin on the ground – in part because we have lacked any way to test ideas experimentally. In that sense, listening carefully to sounds swirling through superfluids could be the stuff of physicists’ dreams, rather than their nightmares. “It’s a success story,” says Liberati. “It’s a case in which theoretical physics finally made connection with experiments.”

    _____________________________________________________________________________________________

    What are black holes made of?

    For all we know, it could be snails and puppy-dog tails. There is no microscopic theory of a black hole’s innards, but Georgi Dvali of the Ludwig Maximilian University of Munich, Germany, thinks we might find clues in parallels between how black holes and Bose-Einstein condensates process information.

    Black holes are careless stewards of information, apparently dribbling it away as they evaporate (see main story), but they are efficient stores of it. It would take about 10-5 electronvolts of energy to stuff one quantum bit of information into a cubic-centimetre box. To stuff that qubit into a black hole of the same size – which would have the mass of Earth – would take 1066 times less energy, says Dvali.

    Intriguingly, Dvali and his colleagues have shown that Bose-Einstein condensates seem to process information similarly to black holes. “There is a one-to-one correspondence,” he says. “In particular, the system delivers very cheap qubits for storing information.”

    Bose-Einstein condensates exist in a so-called quantum-critical state, transitioning from a normal state to one in which all the atoms act as a coherent quantum whole. Dvali speculates that the parallels indicate that black holes are quantum-critical states too – albeit not of atoms, but of quantum particles of gravity known as gravitons.

    _____________________________________________________________________________________________

    *Realization of a sonic black hole analogue in a Bose-Einstein condensate
    Oren Lahav, Amir Itah, Alex Blumkin, Carmit Gordon, Shahar Rinott,
    Alona Zayats, and Jeff Steinhauer
    Technion – Israel Institute of Technology, Haifa, Israel

    **Observation of thermal Hawking radiation and its entanglement in an analogue black hole
    Jeff Steinhauer
    Department of Physics, Technion—Israel Institute of Technology, Technion City, Haifa 32000, Israel

    See the full article here .

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