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  • richardmitnick 1:11 pm on April 15, 2017 Permalink | Reply
    Tags: , , , Black Holes, , EHT - Event Horizon Telescope, , Global mm-VLBI Array   

    From ESO: “Taking the First Picture of a Black Hole” 

    ESO 50 Large

    European Southern Observatory

    30.3.2017

    1. What are the Event Horizon Telescope and the Global mm-VLBI Array?

    At the centre of our galaxy lurks a cosmic monster: a supermassive black hole called Sagittarius A* with a mass about four million times that of the Sun.

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

    Its gravity is so intense that not even light can escape its pull, but if it wasn’t for its strong gravitational influence on the stars and gas around it, we would have no idea that it was there! Now, an ambitious new endeavour is underway to take a never-seen-before image, of the event horizon of the black hole itself.

    Two international collaborations of radio telescopes have linked up to create Earth-sized virtual telescopes: the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA), working at different wavelengths.

    1
    This infographic details the locations of the participating telescopes of the Event Horizon Telescope and the Global mm-VLBI Array. Credit: ESO/O. Furtak

    Global mm-VLBI Array

    Event Horizon Telescope Array

    Event Horizon Telescope map

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

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

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

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    The impressive line-up of telescopes, which stretch across the globe from the South Pole to Hawaii to Europe, will work together to target the supermassive black hole at the heart of the Milky Way.

    To do this, astronomers will exploit a technique known as Very-long-baseline Interferometry (VLBI), where telescopes thousands of kilometres apart can link together and act as one.

    European VLBI

    This cooperative technique can achieve a far higher resolution than any single facility could obtain on its own — a resolution 2000 times that of the NASA/ESA Hubble Space Telescope! This super-high resolution is crucial for detecting the black hole, which — despite being about 20 times bigger than the Sun — lies a long way away, over 26 000 light-years from Earth.

    The plan to image a black hole has been in the works for years, but it’s only recently that technology has brought the ambitious endeavour within reach. Plus, a radio telescope heavyweight has just joined the team: the Atacama Large Millimeter/submillimeter Array (ALMA).

    Located high up on the Chajnantor plateau in Chile’s Atacama Desert, ALMA’s 66 antennas and exquisite receivers make it the largest and most sensitive component of the EHT/GMVA collaboration, increasing the overall sensitivity by a factor of 10. Despite being a state-of-the-art facility, ALMA has undergone several upgrades to take part in the collaboration. Specialist equipment has been installed, including new hard drives that are necessary to store the sheer amount of data produced by the observations, as well as an extremely accurate atomic clock, which is critical to link ALMA to the entire VLBI network.

    The first groundbreaking observations will be made in April 2017: observations at 3 millimetre wavelengths will be made with the GMVA from 1–4 April 2017, and with the EHT at 1.3 millimetre wavelengths from 5–14 April 2017. The GMVA will investigate the properties of the accretion and outflow around the Galactic Centre, while the EHT will attempt to image, for the very first time, the shadow of the black hole’s event horizon.

    There is a long, hard road ahead to process the massive amounts of data that will be acquired during the observation periods, and results are expected to become available towards the end of 2017.

    The outcome of these observations is eagerly awaited by the astronomy community worldwide, as their scientific potential is incredibly exciting and the collaboration are pursuing some awesome goals. These could include testing Einstein’s theory of general relativity, which predicts a roughly circular “shadow” around the black hole. Other goals include learning about how material accretes around black holes, as well as the formation of extremely fast jets of gas that blast out from them.

    3
    Simulated images of the shadow of a black hole: General relativity predicts that the shadow should be circular (middle), but a black hole could potentially also have a prolate (left) or oblate (right) shadow. Future EHT images will test this prediction. Credit: D. Psaltis and A. Broderick.

    This is the first post of a blog series that will take you along for the astronomical ride, giving insight into how cutting-edge research is done and what risks are involved.

    In the following posts, we’ll explore questions such as: What makes black holes so interesting? How do radio telescopes see the Universe? And what do we really know about the supermassive monster lurking at the centre of the Milky Way?

    11.4.2017

    2. What is a black hole?

    Right now, astronomers are attempting to take the first image of the event horizon of the supermassive black hole at the centre of the Milky Way — but what exactly are black holes?

    Black holes are some of the most bizarre and fascinating objects in the Universe. Essentially, they’re reality-bending concentrations of matter squeezed into a very tiny space, creating an object with an immense gravitational pull. Around a black hole is a boundary called an event horizon — the surface beyond which nothing can escape the black hole’s clutches, not even light.

    Take a tour of the anatomy of a black hole with our handy infographic:

    4
    Credit: ESO, ESA/Hubble, M. Kornmesser/N. Bartmann

    Since no light can escape from a black hole, we can’t see them directly. But their huge gravitational influence gives away their presence. Black holes are often orbited by stars, gas and other material in tight paths that become more crowded and frantic as they’re dragged closer to the event horizon. This creates a superheated accretion disc around the black hole, which emits vast amounts of radiation of different wavelengths.

    By observing this radiation from the activity around black holes, astronomers have determined that there are two main types: stellar mass and supermassive.

    A stellar mass black hole is the corpse of a star more than about 30 times as massive as our Sun. At the end of its life, such stars violently collapse and don’t stopped collapsing until all of their constituent matter has condensed down into an unimaginably tiny space. It’s easiest to discover stellar mass black holes that are part of an X-ray binary system, where the black hole is guzzling down material from its companion star.

    5
    Artist’s impression of the formation of a stellar black hole in a binary system. Credit: ESO/L. Calçada/M.Kornmesser

    The second type is called a supermassive black hole. These gargantuan black holes are up to billions of times more massive than an average star, and how they formed is much less clear and is a matter of ongoing study. One theory proposes they formed from enormous clouds of matter that collapsed when galaxies first formed; another theory suggests that colliding stellar mass black holes can merge into one enormous object.

    Today, these supermassive monsters reside at the centres of almost every galaxy — including our own Milky Way. They exert tremendous influence on their home galaxies, especially when they gorge on gas and stars.

    6
    Artist’s impression of a gas cloud after a close approach to the black hole at the centre of the Milky Way. The star orbiting the black hole are shown, along with blue lines that mark their fast, tight orbits. Credit: ESO/MPE/Marc Schartmann

    26 000 light-years away from Earth, Sagittarius A* (Sgr A* for short) is the supermassive black hole in the hot, violent centre of the Milky Way. It’s over 4 million times more massive than our Sun, over 20 million kilometres across, and is spinning at a large fraction of the speed of light. It’s shrouded from optical telescopes by dense clouds of dust and gas, so observatories that can observe different wavelengths — either longer (such as ALMA) or shorter (X-ray telescopes) — are essential to study its properties.

    Soon, through the combined power of ALMA and other millimetre-wavelength telescopes across the globe, we may become much better acquainted with the monstrous heart of our galaxy. The Global mm-VLBI Array is currently investigating the process of how gas, dust and other material accrete onto supermassive black holes, as well as the formation of the extremely fast gas jets that flow from them. The Event Horizon Telescope, on the other hand, is working towards a different goal: imaging the shadow of the event horizon, the point of no return.

    This is the second post of a blog series following the EHT and GMVA projects. Stay tuned to find out more about why the event horizon of a black hole is so interesting!

    Event Horizon Telescope website
    GMVA website
    BlackHoleCam — an EU-funded project to finally image, measure and understand astrophysical black holes
    Read more about ALMA
    Find out more about ALMA’s VLBI capabilities

    See the full article here .

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    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

    ESO LaSilla
    ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres

    ESO VLT
    VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO Vista Telescope
    ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO NTT
    ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres

    ESO VLT Survey telescope
    VLT Survey Telescope at Cerro Paranal with an elevation of 2,635 metres (8,645 ft) above sea level

    ALMA Array
    ALMA on the Chajnantor plateau at 5,000 metres

    ESO E-ELT
    ESO/E-ELT to be built at Cerro Armazones at 3,060 m

    ESO APEX
    APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert

     
    • Nikola Milovic 8:48 am on April 16, 2017 Permalink | Reply

      I wish I could make contact with scientists who are trying to learn something more about black holes. The main reason for this contact is my view that science still does not know what a black hole is and how and why it occurs.
      It is true that this is a place where even light can not escape. But, one must know the limits of long acting black hole and what happens within those boundaries towards the center of the black hole and outside those borders where both matter and light still “confused” and do not know which way to go. To be deciphered. What if scientists to “see” with new telescopes, is again out of the black hole and its limits where the “forbidden transition both sides of the border.
      It is true that this is an enormous amount of gravity, but how and why this occurs, science can not know if you do not know the structure of the universe.
      The black hole has a spherical shape and is situated so that all sides around this sphere can “suck every form of matter. The fact that science sees as the horizon, not what is in reality, neither of the black hole can form any kind of matter, nor can they be two black holes collide.

      Like

  • richardmitnick 8:18 am on March 31, 2017 Permalink | Reply
    Tags: , , , Black Holes, , , direct collapse black hole ala Avi Loeb   

    From COSMOS: “When giants warped the universe” 

    Cosmos Magazine bloc

    COSMOS

    31 March 2017
    Graham Phillips

    1
    They don’t make them like they used to: supermassive black holes emerged billions of years earlier than thought. Getty Images

    They gobble stars, bend space, warp time and may even provide gateways to other universes.

    Black holes fire the imagination of scientists and science-fiction aficionados alike. But at least one thing about them wasn’t all that mind-bending: we’ve long understood black holes to be the end point in the life of a big star, when it runs out of fuel and collapses on itself.

    However, in recent times astronomers have been confronted with a paradox: gigantic black holes that existed when the universe was less than a billion years old.

    Since average-sized black holes take many billions of years to form, astrophysicists have been scratching their heads to figure out how these monsters could have arisen so early. It now seems that rather than being the end game in the evolution of stars and galaxies, supermassive black holes were around at their beginnings and played a major role in shaping them.

    Recommended reading: The bright side of black holes

    It was the little known English clergyman and scientist John Michell who, in 1783, first articulated the idea of “dark stars” whose gravity was so great they would prevent light from escaping them. The concept was astonishingly prescient even if parts of his theory – particularly those based on Newton’s idea that light particles had mass – were flawed.

    The first accurate description of black holes came in 1916 from German physicist and astronomer Karl Schwarzschild. Schwarzschild was serving in the German Army at the time, despite already being over 40 years of age.

    After seeing action on both the western and eastern fronts, Schwarzschild was sent home due to a serious auto-immune skin disease, pemphigus.

    It was late 1915 and Einstein’s theory of General Relativity had just been published. Inspired, Schwarzschild lost no time writing a paper that predicted the existence of black holes; it was published just months before he succumbed to his disease in May 1916.

    According to Einstein’s theory, the force of gravity was the result of a mass distorting the fabric of space-time. In the same way that a bowling ball dimples the fabric of a trampoline, a star’s mass dimpled the space-time fabric of its system, keeping planets circling around it.

    The theory was underpinned by equations laying out the interaction of energy, mass, space and time. Schwarzschild’s achievement was to apply Einstein’s equations to a simplified scenario: a perfectly spherical star. One of the things that jumped out of his mathematical musings was an object with such a strong gravitational pull that not even light could escape it.

    While Schwarzschild’s idea made sense in the theoretical realm of mathematics, most physicists did not expect to find an exemplar in the real universe.

    By the 1960s, however, expectations were changing. Astronomers discovered the existence of extremely dense objects known as neutron stars. Detected by their unusual pulsing of electromagnetic radiation, they were the dense corpses of large stars that had exhausted their fuel. Without the force of the burning fuel pushing against their own gravity, they collapsed, compressing their matter until only the pressure of neutron against neutron halted the crush.

    Neutron stars got astrophysicists thinking back to Schwarzschild’s idea. What happens when really big suns with even stronger gravity cave in? All the matter would be squeezed down to a point with an extraordinarily strong gravitational field.

    Sometime in the 1960s, physicists coined the term “black hole”, and the hunt for something more than just a mathematical artefact was on.

    The first evidence that black holes weren’t just theoretical came in 1964, when a rocket decked with sensitive instruments was shot into sub-orbital space. It detected suspicious X-rays emanating from the constellation of Cygnus (the swan).

    The X-ray source became known as Cygnus X-1. By the early 1970s most astronomers inferred the X-rays were radiated by super-heated matter being sucked into the gravitational field of the black hole. It would take decades more, however, before the first conclusive evidence that black holes exist and obey Einstein’s equations of general relativity.

    This came in September 2015 with the detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States.



    Caltech/MIT Advanced aLigo Hanford, WA, USA installation

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


    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    These ripples in the fabric of space-time had been generated by two black holes colliding 1.3 billion years ago. Theorists had predicted that if such a titanic event occurred somewhere in our galaxy, the reverberations should be measurable on Earth.


    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    LIGO’s detection of gravitational waves thus also confirmed the existence of black holes. Yet even as the evidence that black holes truly exist has firmed up, our understanding of how they arise seems to be crumbling.

    The cracks in the theory grew gradually as astronomers accumulated evidence for the existence of a very different kind of black hole. While most black holes have a mass that is equivalent to 10-100 times that of our Sun, these monsters were equivalent to a million or a billion solar masses. With typical prosaicness, astronomers dubbed them supermassive black holes.

    Unlike smaller black holes, they also resided at the centres of galaxies. Most surprising of all, far-reaching telescopes like the European Southern Observatory’s Very Large Telescope detected them in extremely distant galaxies.


    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    Because of the extreme length of time it takes for their light to reach Earth, these galaxies provide snapshots of the universe in its infancy.

    “A billion years after the big bang you have black holes that are as massive as the biggest black holes we find around us today,” says Avi Loeb, an astrophysicist at Harvard University.

    That simply doesn’t make sense according to the accepted understanding that black holes come only at the end of a star’s life. “It’s sort of like going to the delivery room in a hospital and finding giant babies.”

    Were these monster babies the result of many black holes colliding? Or did they arise from moderately sized black holed that ballooned by feeding on gas and other stars? Neither of these scenarios sits well with astrophysicists.

    “Getting from even a hundred solar masses up to several billion solar masses in less than a billion years is quite challenging,” says Mitch Begelman, an astrophysicist from the University of Colorado. “Black holes are not vacuum cleaners. That’s a popular misconception. It’s very difficult to get a black hole to swallow lots of stuff [in a short period of time].”

    Loeb, who has been captivated by supermassive black holes since he got into astrophysics, thinks he might have a solution to the mystery: in 1994, he came up with the idea that a different kind of process gave birth to black holes in the early universe.

    In the modern universe, a black hole takes billions of years to form. The black hole’s precursor star (which must be greater than 10 solar masses to muster the required gravitational force) must first burn through its fuel, then explode as a supernova before it collapses.

    But while the biggest stars today reach the size of 300 solar masses, the early universe might have blazed with stars equivalent to as much as a million solar masses. Such a super star, according to Loeb’s calculations, would burn so feverishly it would use up its fuel in just a million years.

    Then it would collapse directly into a black hole a million times the mass of the Sun – what Loeb calls “a direct collapse black hole”.

    According to Loeb, the reason super stars were formed only in the embryonic universe, is because back then stars were made of simpler stuff: “The gas was pristine. It came from the big bang and had only hydrogen and helium,” he explains.

    Lacking heavier elements to radiate heat, the clouds stayed relatively warm. That allowed them to grow without fragmenting, forming super stars.

    By contrast, in today’s universe star dust contains heavy atoms like carbon, silicon and oxygen – forged in the nuclear furnaces of the first generation of stars and blown throughout the cosmos when those stars exploded.

    As result, modern-day dust clouds can cool to extremely low temperatures and fragment, mostly forming stars about the size of the Sun.

    If Loeb is right, early super stars gave rise to the direct collapsers, which gave rise to supermassive black holes. These monsters have had an enormous influence on how the universe evolved. They shaped galaxies in two ways.

    First, they gobbled up clouds and stars in their immediate vicinity. Second, like some cosmic air blower, they beamed out jets of energy that propelled dust and gas out of their galaxy.

    “Within tens of millions of years the black holes can remove the gas from the host galaxy,” Loeb says. By cleaning the galaxy of the raw material for star creation and growth, the black holes have capped the size of galaxies.

    If not for the supermassive black hole at the centre of the Milky Way, Loeb estimates, our galaxy could have grown a thousand times bigger than it is today. That would be some night sky to look up at.

    “The growth of black holes seems to be a crucial element in galaxy formation,” Begelman agrees. “Galaxies would look very different if there weren’t these black holes.”

    Of course, the absolute proof that direct collapse black holes exist will come when one is observed.

    In the past year astronomers have seen some tantalising clues. One is a galaxy known as CR7, which hosts a source of light much brighter than its stars – perhaps the radiation caused by a black hole sucking in gas.

    “You see evidence for a galaxy that has mainly hydrogen and helium,” Loeb says. “That could potentially be the birthplace of a direct collapse black hole.”

    See the full article here .

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  • richardmitnick 1:31 pm on March 28, 2017 Permalink | Reply
    Tags: , Black Holes, , , , , SUPERRADIANCE   

    From PI via GIZMODO: “Mind-Blowing New Theory Connects Black Holes, Dark Matter, and Gravitational Waves” 

    Perimeter Institute
    Perimeter Institute

    GIZMODO

    3.28.17
    Ryan F. Mandelbaum

    The past few years have been incredible for physics discoveries. Scientists spotted the Higgs boson, a particle they’d been hunting for almost 50 years, in 2012, and gravitational waves, which were theorized 100 years ago, in 2016. This year, they’re slated to take a picture of a black hole. So, thought some theorists, why not combine all of the craziest physics ideas into one, a physics turducken? What if we, say, try to spot the dark matter radiating off of black holes through their gravitational waves?

    It’s really not that strange of an idea. Now that scientists have detected gravitational waves, ripples in spacetime spawned by the most violent physical events, they want to use their discovery to make real physics observations. They think they have a way to spot all-new particles that might make up dark matter, an unknown substance that accounts for over 80 percent of all of the gravity in the universe.

    The basic idea is that we’re trying to use black holes… the densest, most compact objects in the universe, to search for new kinds of particles,” Masha Baryakhtar, postdoctoral researcher at the Perimeter Institute for Theoretical Physics in Canada, told Gizmodo. Especially one particle: “The axion. People have been looking for it for 40 years.”

    Black holes are the universe’s sinkholes, so strong that light can’t escape their pull once it’s entered. They’ve got such powerful gravitational fields that they produce gravitational waves when they collide with each other. Dark matter might not be made from particles (specks of mass and energy), but if it was, we might observe it as axions, particles around one quintillion (a billion billion) times lighter than an electron, hanging around black holes. Now that you understand all the terms, here’s how the theory works.

    Baryakhtar and her teammates think that black holes are more than just bear traps for light, but nuclei at the center of a sort of gravitational atom. The axions would be the electrons, so to speak. If you already know about black holes, you know they have incredibly hot, high-energy discs of gas orbiting them, produced by the friction between particles accelerated by the black hole’s gravity. This theory ignores that stuff, since axions wouldn’t interact via friction.

    Keeping with the atom analogy, the axions can jump around the black hole, gaining and losing energy the same way that electrons do. But electrons interact via electromagnetism, so they let out electromagnetic waves, or light waves. Axions interact via gravity, so they let out gravitational waves. But like I said earlier, axions are tiny. Unlike a tiny atom, the black hole in these “gravity atoms” rotates, supercharging the space around it and coaxing it into producing more axions. Despite the axion’s tiny mass, this so-called superradiance process could generate 10^80 axions, the same number of atoms in the entire universe, around a single black hole. Are you still with me? Crazy spinning blob makes lots of crazy stuff.

    Craziest of all, we should be able to hear a gravitational wave hum from these axions moving around and releasing gravitational waves in our detectors, similar to the way you see spectral lines coming off of electrons in atoms in chemistry class. “You’d see this at a particular frequency which would be roughly twice the axion mass,” said Baryakhtar.

    There are giant gravitational wave detectors scattered around the world; presently there’s one called LIGO (Laser Interferometer Gravitational Wave Observatory) in Washington State, another LIGO in Louisiana, and one called Virgo in Italy that are sensitive enough to detect gravitational waves, and with upgrades, to detect axions and prove their theory right.



    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


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



    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Scientists would essentially need to record data, play it back, and tune their analysis like a radio to pick up the signal at just the right frequency.

    There are other ways the team thinks it could spot this superradiance effect, by measuring the spins in sets of colliding black holes. If black holes really do produce axions, scientists would see very few quickly-spinning black holes in collisions, since the superradiance effects would slow down some of the colliding black holes and create a visible effect in the data, according to the research published this month in the journal Physical Review D. The black hole spins would have a specific pattern which we should be able to spot in the gravitational wave detector data.

    Other scientists were immediately excited about this paper. “I’m always super excited about new ways to detect my favorite pet particle, the axion! Also, SUPERRADIANCE!” Dr. Chanda Prescod-Weinstein, the University of Washington axion wrangler, told Gizmodo in an email. “It’s so cool, and I haven’t read a paper that talked about [superradiance] in years. So it was really fun to see superradiance and axions in one paper.”

    There are a few drawbacks, as there are with any theory. These theorized black hole atoms would have to produce axions of a certain mass, but that mass isn’t an ideal one for the axion to be a dark matter particle, said Prescod-Weinstein. Plus, the second detection idea, the one that looks at the spin rate of colliding black holes, might not work. “They say [in the paper] that they don’t take into account the potential influence of another black hole” in the colliding pair, Dr. Lionel London, a research associate at Cardiff University School of Physics and Astronomy specializing in gravitational wave modeling, told Gizmodo. “If this does turn out to be a significant effect and they’re not including it, this could cast doubt on their results.” But there’s hope. “There’s good reason to believe the effect of a companion [black hole] won’t be large.”

    When would we spot these kinds of events? As of now, the LIGO and Virgo gravitational wave detectors probably aren’t ready. “With the current sensitivity we’re on the edge” of detecting axions, said Baryakhtar. “But LIGO will continue improving their instruments and at design sensitivity we might be able to see as many as 1000s of these axion signals coming in,” she said. Thousands of hums from these black hole-atoms.

    So, if you’ve gotten all the way to this point of the story and still don’t understand what’s going on, a recap: We’ve got these gravitational wave detectors that cost hundreds of millions of dollars each, that are good at spotting really crazy things going on in the universe. Theorists have come up with an interesting way to use them to solve one of the most important interstellar mysteries: What the heck is dark matter? As with most new ideas in theoretical physics, this is something cool to think about and isn’t ready for the big time… yet.

    “I think that timescale is always a concern, but we’re just getting started with LIGO discoveries,” said Prescod-Weinstein. “So who knows what’s around the corner over the next 10 years.”

    See the full article here .

    Please help promote STEM in your local schools.

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    About Perimeter

    Perimeter Institute is the world’s largest research hub devoted to theoretical physics. The independent Institute was founded in 1999 to foster breakthroughs in the fundamental understanding of our universe, from the smallest particles to the entire cosmos. Research at Perimeter is motivated by the understanding that fundamental science advances human knowledge and catalyzes innovation, and that today’s theoretical physics is tomorrow’s technology. Located in the Region of Waterloo, the not-for-profit Institute is a unique public-private endeavour, including the Governments of Ontario and Canada, that enables cutting-edge research, trains the next generation of scientific pioneers, and shares the power of physics through award-winning educational outreach and public engagement.

     
  • richardmitnick 10:26 am on March 16, 2017 Permalink | Reply
    Tags: , , , Black Holes, ,   

    From MIT: “Scientists identify a black hole choking on stardust” 

    MIT News

    MIT Widget

    MIT News

    March 14, 2017
    Jennifer Chu

    1
    In this artist’s rendering, a thick accretion disk has formed around a supermassive black hole following the tidal disruption of a star that wandered too close. Stellar debris has fallen toward the black hole and collected into a thick chaotic disk of hot gas. Flashes of X-ray light near the center of the disk result in light echoes that allow astronomers to map the structure of the funnel-like flow, revealing for the first time strong gravity effects around a normally quiescent black hole.
    Image: NASA/Swift/Aurore Simonnet, Sonoma State University

    Data suggest black holes swallow stellar debris in bursts.

    In the center of a distant galaxy, almost 300 million light years from Earth, scientists have discovered a supermassive black hole that is “choking” on a sudden influx of stellar debris.

    In a paper published today in Astrophysical Journal Letters, researchers from MIT, NASA’s Goddard Space Flight Center, and elsewhere report on a “tidal disruption flare” — a dramatic burst of electromagnetic activity that occurs when a black hole obliterates a nearby star. The flare was first discovered on Nov. 11, 2014, and scientists have since trained a variety of telescopes on the event to learn more about how black holes grow and evolve.

    The MIT-led team looked through data collected by two different telescopes and identified a curious pattern in the energy emitted by the flare: As the obliterated star’s dust fell into the black hole, the researchers observed small fluctuations in the optical and ultraviolet (UV) bands of the electromagnetic spectrum. This very same pattern repeated itself 32 days later, this time in the X-ray band.

    The researchers used simulations of the event performed by others to infer that such energy “echoes” were produced from the following scenario: As a star migrated close to the black hole, it was quickly ripped apart by the black hole’s gravitational energy. The resulting stellar debris, swirling ever closer to the black hole, collided with itself, giving off bursts of optical and UV light at the collision sites. As it was pulled further in, the colliding debris heated up, producing X-ray flares, in the same pattern as the optical bursts, just before the debris fell into the black hole.

    “In essence, this black hole has not had much to feed on for a while, and suddenly along comes an unlucky star full of matter,” says Dheeraj Pasham, the paper’s first author and a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research. “What we’re seeing is, this stellar material is not just continuously being fed onto the black hole, but it’s interacting with itself — stopping and going, stopping and going. This is telling us that the black hole is ‘choking’ on this sudden supply of stellar debris.”

    Pasham’s co-authors include MIT Kavli postdoc Aleksander Sadowski and researchers from NASA’s Goddard Space Flight Center, the University of Maryland, the Harvard-Smithsonian Center for Astrophysics, Columbia University, and Johns Hopkins University.

    See the full article here .

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  • richardmitnick 9:02 am on March 2, 2017 Permalink | Reply
    Tags: , , Black Holes, , , Rapid changes point to origin of ultra-fast black hole winds   

    From ESA: “Rapid changes point to origin of ultra-fast black hole winds” 

    ESA Space For Europe Banner

    European Space Agency

    1 March 2017
    Markus Bauer








    ESA Science and Robotic Exploration Communication Officer









    Tel: +31 71 565 6799









    Mob: +31 61 594 3 954









    Email: markus.bauer@esa.int

    Michael Parker
    Institute of Astronomy, Cambridge, UK
    Email: mlparker@ast.cam.ac.uk

    Andrew Fabian
    Institute of Astronomy, Cambridge, UK
    Email: acf@ast.cam.ac.uk

    Norbert Schartel
    XMM-Newton project scientist
    Email: Norbert.Schartel@esa.int

    1
    Black hole with ultrafast winds. No image credit

    ESA and NASA space telescopes have made the most detailed observation of an ultra-fast wind flowing from the vicinity of a black hole at nearly a quarter of the speed of light.

    Outflowing gas is a common feature of the supermassive black holes that reside in the centre of large galaxies. Millions to billions of times more massive than the Sun, these black holes feed off the surrounding gas that swirls around them. Space telescopes see this as bright emissions, including X-rays, from the innermost part of the disc around the black hole.

    Occasionally, the black holes eat too much and burp out an ultra-fast wind. These winds are an important characteristic to study because they could have a strong influence on regulating the growth of the host galaxy by clearing the surrounding gas away and therefore suppressing the birth of stars.

    Using ESA’s XMM-Newton and NASA’s NuStar telescopes, scientists have now made the most detailed observation yet of such an outflow, coming from an active galaxy identified as IRAS 13224–3809.

    ESA/XMM Newton
    ESA/XMM Newton

    NASA/NuSTAR
    NASA/NuSTAR

    The winds recorded from the black hole reach 71 000 km/s – 0.24 times the speed of light – putting it in the top 5% of fastest known black hole winds.

    XMM-Newton focused on the black hole for 17 days straight, revealing the extremely variable nature of the winds.

    “We often only have one observation of a particular object, then several months or even years later we observe it again and see if there’s been a change,” says Michael Parker of the Institute of Astronomy at Cambridge, UK, lead author of the paper published in Nature this week that describes the new result.

    “Thanks to this long observation campaign, we observed changes in the winds on a timescale of less than an hour for the first time.”

    The changes were seen in the increasing temperature of the winds, a signature of their response to greater X-ray emission from the disc right next to the black hole.

    Furthermore, the observations also revealed changes to the chemical fingerprints of the outflowing gas: as the X-ray emission increased, it stripped electrons in the wind from their atoms, erasing the wind signatures seen in the data.

    “The chemical fingerprints of the wind changed with the strength of the X-rays in less than an hour, hundreds of times faster than ever seen before,” says co-author Andrew Fabian, also from the Institute of Astronomy and principal investigator of the project.

    “It allows us to link the X-ray emission arising from the infalling material into the black hole, to the variability of the outflowing wind farther away.”

    “Finding such variability, and finding evidence for this link, is a key step in understanding how black hole winds are launched and accelerated, which in turn is an essential part of understanding their ability to moderate star formation in the host galaxy,” adds Norbert Schartel, ESA’s XMM-Newton project scientist.

    The response of relativistic outflowing gas to the inner accretion disk of a black hole,” by M. Parker et al. is published in Nature.

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 6:27 pm on February 19, 2017 Permalink | Reply
    Tags: , , , Black Holes, , , NAOJ Nobeyama Radio Observatory, Supernova Remnant W44   

    From EarthSky: “Hints of a quiet, stray black hole” 

    1

    EarthSky
    Via NAOJ Nobeyama Radio Observatory
    No writer credit

    1
    Supernova Remnant W44. https://earthspacecircle.blogspot.com/2015/12/supernova-remnant-w44.html

    Graduate student Masaya Yamada and professor Tomoharu Oka, both of Keio University, led a research team that was surveying gas clouds around the supernova remnant W44, located 10,000 light-years away from us, when they noticed something unusual. Their statement explained:

    “During the survey, the team found a compact molecular cloud with enigmatic motion. This cloud, [nicknamed] the ‘Bullet,’ has a speed of more than 100 km/second [60 miles/second], which exceeds the speed of sound in interstellar space by more than two orders of magnitude. In addition, this cloud, with the size of two light-years, moves backward against the rotation of the Milky Way galaxy.”

    The energy of motion of the Bullet is many times larger than that injected by the original W44 supernova. The astronomers think this energy must come from a quiet, stray black hole, and they proposed two scenarios to explain the Bullet:

    ” In both cases, a dark and compact gravity source, possibly a black hole, has an important role. One scenario is the ‘explosion model’ in which an expanding gas shell of the supernova remnant passes by a static black hole. The black hole pulls the gas very close to it, giving rise to an explosion, which accelerates the gas toward us after the gas shell has passed the black hole. In this case, the astronomers estimated that the mass of the black hole would 3.5 times the solar mass or larger.

    The other scenario is the ‘irruption model’ in which a high speed black hole storms through a dense gas and the gas is dragged along by the strong gravity of the black hole to form a gas stream. In this case, researchers estimated the mass of the black hole would be 36 times the solar mass or larger. With the present dataset, it is difficult for the team to distinguish which scenario is more likely.”

    Via NAOJ Nobeyama Radio Observatory

    ASTE Atacama Submillimeter telescope
    ASTE Atacama Submillimeter telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Telescope

    3
    (a) CO (J=3-2) emissions (color) and 1.4 GHz radio continuum emissions (contours) around the supernova remnant W44. (b) Galactic longitude-velocity diagram of CO (J=3-2) emissions at the galactic latitude of -0.472 degrees. (c -f): Galactic longitude-velocity diagrams of the Bullet in CO (J=1-0), CO (J=3-2), CO (J=4-3), and HCO+ (J=1-0), from left to right. Galactic longitude-velocity diagrams show the speed of the gas at a specific position. Structures elongated in the vertical direction in the diagrams have a large velocity width. Credit: Yamada et al. (Keio University), NAOJ

    4
    Schematic diagrams of two scenarios for the formation mechanism of the Bullet. (a) explosion model and (b) irruption model. Both diagrams show a part of the shock front produced by the expansion of the supernova remnant W44. The shock wave enters into quiescent gas and compresses it to form dense gas. The Bullet is located in the center of the diagram and has completely different motion compared to the surrounding gas. Credit: Yamada et al. (Keio University)

    These astronomers published their findings in January, 2017 in the peer-reviewed Astrophysical Journal Letters.

    A black hole is a place in space where matter is squeezed into a tiny space, and where gravity pulls so hard that even light can’t escape. Black holes are black. No light comes from them. Up to now, most known stellar black holes are those with companion stars. The black hole pulls gas from the companion, which piles up around it and forms a disk. The disk heats up due to the enormous gravitational pull by the black hole and emits intense radiation.

    On the other hand, if a black hole is floating alone in space – as many must be – its lack of light or any sort of emission would make it very, very hard to find.

    See the full article here .

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  • richardmitnick 1:46 pm on February 8, 2017 Permalink | Reply
    Tags: Black Holes, ,   

    From CfA: “A Middleweight Black Hole is Hiding at the Center of a Giant Star Cluster” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    February 8, 2017
    Christine Pulliam
    Media Relations Manager
    Harvard-Smithsonian Center for Astrophysics
    617-495-7463
    cpulliam@cfa.harvard.edu

    1
    In this artist’s illustration, an intermediate-mass black hole in the foreground distorts light from the globular star cluster in the background. New research suggests that a 2,200 solar-mass black hole resides at the center of the globular cluster 47 Tucanae. CfA / M. Weiss

    2
    This artist’s conception shows another representation of the intermediate-mass black hole that may lurk in the center of the globular cluster 47 Tucanae. B. Kızıltan & T. Karacan

    All known black holes fall into two categories: small, stellar-mass black holes weighing a few Suns, and supermassive black holes weighing millions or billions of Suns. Astronomers expect that intermediate-mass black holes weighing 100 – 10,000 Suns also exist, but so far no conclusive proof of such middleweights has been found. Today, astronomers are announcing new evidence that an intermediate-mass black hole (IMBH) weighing 2,200 Suns is hiding at the center of the globular star cluster 47 Tucanae.

    “We want to find intermediate-mass black holes because they are the missing link between stellar-mass and supermassive black holes. They may be the primordial seeds that grew into the monsters we see in the centers of galaxies today,” says lead author Bulent Kiziltan of the Harvard-Smithsonian Center for Astrophysics (CfA).

    This work appears in the Feb. 9, 2017, issue of the prestigious science journal Nature.

    47 Tucanae is a 12-billion-year-old star cluster located 13,000 light-years from Earth in the southern constellation of Tucana the Toucan. It contains hundreds of thousands of stars in a ball only about 120 light-years in diameter. It also holds about two dozen pulsars that were important targets of this investigation.

    47 Tucanae has been examined for a central black hole before without success. In most cases, a black hole is found by looking for X-rays coming from a hot disk of material swirling around it. This method only works if the black hole is actively feeding on nearby gas. The center of 47 Tucanae is gas-free, effectively starving any black hole that might lurk there.

    The supermassive black hole at the center of the Milky Way also betrays its presence by its influence on nearby stars. Years of infrared observations have shown a handful of stars at our galactic center whipping around an invisible object with a strong gravitational tug. But the crowded center of 47 Tucanae makes it impossible to watch the motions of individual stars.

    The new research relies on two lines of evidence. The first is overall motions of stars throughout the cluster. A globular cluster’s environment is so dense that heavier stars tend to sink to the center of the cluster. An IMBH at the cluster’s center acts like a cosmic “spoon” and stirs the pot, causing those stars to slingshot to higher speeds and greater distances. This imparts a subtle signal that astronomers can measure.

    By employing computer simulations of stellar motions and distances, and comparing them with visible-light observations, the team finds evidence for just this sort of gravitational stirring.

    The second line of evidence comes from pulsars, compact remnants of dead stars whose radio signals are easily detectable. These objects also get flung about by the gravity of the central IMBH, causing them to be found at greater distances from the cluster’s center than would be expected if no black hole existed.

    Combined, this evidence suggests the presence of an IMBH of about 2,200 solar masses within 47 Tucanae.

    Since this black hole has eluded detection for so long, similar IMBHs may be hiding in other globular clusters. Locating them will require similar data on the positions and motions of both the stars and any pulsars within the clusters.

    See the full article here .

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 4:07 pm on February 2, 2017 Permalink | Reply
    Tags: , , , Black Holes, , , Tail of Stray Black Hole hiding in the Milky Way   

    From NAOJ: “Tail of Stray Black Hole hiding in the Milky Way” 

    NAOJ

    NAOJ

    2017 Feb 02
    No writer credit found

    By analyzing the gas motion of an extraordinarily fast-moving cosmic cloud in a corner of the Milky Way, astronomers found hints of a wandering black hole hidden in the cloud. This result marks the beginning of the search for quiet black holes; millions of such objects are expected to be floating in the Milky Way although only dozens have been found to date.

    1
    Figure 1. Artist’s impression of a stray black hole storming through a dense gas cloud. The gas is dragged along by the strong gravity of the black hole to form a narrow gas stream. Credit: Keio University

    It is difficult to find black holes, because they are completely black. In some cases black holes cause effects which can be seen. For example if a black hole has a companion star, gas streaming into the black hole piles up around it and forms a disk. The disk heats up due to the enormous gravitational pull by the black hole and emits intense radiation. But if a black hole is floating alone in space, no emissions would be observable coming from it.

    A research team led by Masaya Yamada, a graduate student at Keio University, Japan, and Tomoharu Oka, a professor at Keio University, used the ASTE Telescope in Chile and the 45-m Radio Telescope at Nobeyama Radio Observatory, both operated by the National Astronomical Observatory of Japan, to observe molecular clouds around the supernova remnant W44, located 10,000 light-years away from us. Their primary goal was to examine how much energy was transferred from the supernova explosion to the surrounding molecular gas, but they happened to find signs of a hidden black hole at the edge of W44.

    NAOJ Atacama Submillimeter Telescope Experiment (ASTE)  deployed to its site on Pampa La Bola, near Cerro Chajnantor and the Llano de Chajnantor Observatory in northern Chile
    NAOJ Atacama Submillimeter Telescope Experiment (ASTE) deployed to its site on Pampa La Bola, near Cerro Chajnantor and the Llano de Chajnantor Observatory in northern Chile

    NAOJ Nobeyama Radio Observatory, located near Minamimaki, Nagano at an elevation of 1350m
    NAOJ Nobeyama Radio Observatory, located near Minamimaki, Nagano at an elevation of 1350m

    During the survey, the team found a compact molecular cloud with enigmatic motion. This cloud, named the “Bullet,” has a speed of more than 100 km/s, which exceeds the speed of sound in interstellar space by more than two orders of magnitude. In addition, this cloud, with the size of two light-years, moves backward against the rotation of the Milky Way Galaxy.

    To investigate the origin of the Bullet, the team performed intensive observations of the gas cloud with ASTE and the Nobeyama 45-m Radio Telescope. The data indicate that the Bullet seems to jump out from the edge of the W44 supernova remnant with immense kinetic energy. “Most of the Bullet has an expanding motion with a speed of 50 km/s, but the tip of the Bullet has a speed of 120 km/s,” said Yamada. “Its kinetic energy is a few tens of times larger than that injected by the W44 supernova. It seems impossible to generate such an energetic cloud under ordinary environments.”

    3
    Figure 3. (a) CO (J=3-2) emissions (color) and 1.4 GHz radio continuum emissions (contours) around the supernova remnant W44. (b) Galactic longitude-velocity diagram of CO (J=3-2) emissions at the galactic latitude of -0.472 degrees. (c -f): Galactic longitude-velocity diagrams of the Bullet in CO (J=1-0), CO (J=3-2), CO (J=4-3), and HCO+ (J=1-0), from left to right. Galactic longitude-velocity diagrams show the speed of the gas at a specific position. Structures elongated in the vertical direction in the diagrams have a large velocity width. Credit: Yamada et al. (Keio University), NAOJ

    The team proposed two scenarios for the formation of the Bullet. In both cases, a dark and compact gravity source, possibly a black hole, has an important role. One scenario is the “explosion model” in which an expanding gas shell of the supernova remnant passes by a static black hole. The black hole pulls the gas very close to it, giving rise to an explosion, which accelerates the gas toward us after the gas shell has passed the black hole. In this case, the astronomers estimated that the mass of the black hole would 3.5 times the solar mass or larger. The other scenario is the “irruption model” in which a high speed black hole storms through a dense gas and the gas is dragged along by the strong gravity of the black hole to form a gas stream. In this case, researchers estimated the mass of the black hole would be 36 times the solar mass or larger. With the present dataset, it is difficult for the team to distinguish which scenario is more likely.

    4
    Figure 4. Schematic diagrams of two scenarios for the formation mechanism of the Bullet. (a) explosion model and (b) irruption model. Both diagrams show a part of the shock front produced by the expansion of the supernova remnant W44. The shock wave enters into quiescent gas and compresses it to form dense gas. The Bullet is located in the center of the diagram and has completely different motion compared to the surrounding gas. Yamada et al. (Keio University)

    Theoretical studies have predicted that 100 million to 1 billion black holes should exist in the Milky Way, although only 60 or so have been identified through observations to date. “We found a new way of discovering stray black holes,” said Oka. The team expects to disentangle the two possible scenarios and find more solid evidence for a black hole in the Bullet with higher resolution observations using a radio interferometer, such as the Atacama Large Millimeter/submillimeter Array (ALMA).

    These observation results were published as Yamada et al. Kinematics of Ultra-high-velocity Gas in the Expanding Molecular Shell adjacent to the W44 Supernova Remnant in the Astrophysical Journal Letters in January 2017.
    The research team members are: Masaya Yamada, Tomoharu Oka, Shunya Takekawa, Yuhei Iwata, Shiho Tsujimoto, Sekito Tokuyama, Maiko Furusawa, Keisuke Tanabe, and Mariko Nomura, from Keio University, Japan.

    This research was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science (No. 15H03643).

    See the full article here .

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    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior
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    ALMA Array
    ALMA

    sft
    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

     
  • richardmitnick 10:38 am on January 25, 2017 Permalink | Reply
    Tags: , , , Black Hole Orbits: Zoom-Whirls and Four-Leaf Clovers, Black Holes, Innermost Bound Circular Orbit (IBCO), Innermost Stable Circular Orbit (ISCO), Perihelion, Periodic table of the weird and wonderful orbits around black holes   

    From astrobites: “Black Hole Orbits: Zoom-Whirls and Four-Leaf Clovers” 

    Astrobites bloc

    Astrobites

    Jan 25, 2017
    Lisa Drummond

    Title: A periodic table for black hole orbits
    Authors: Janna Levin and Gabe Perez-Giz
    First Author’s Institution: Barnard College of Columbia University, New York
    1
    Status: Published in Phys. Rev. D, open access

    Orbits around a black hole can be fascinatingly intricate. Surprisingly, the simple precessing ellipse we observe in planetary motion is not what we see close to a black hole. Rather these orbits exhibit something called “zoom-whirl” behaviour, tracing out patterns that look like four-leaf clovers. The authors concentrate especially on periodic orbits and catalogue these orbits into a “periodic table” according to their main features.

    Anomalous precession of Mercury

    2
    Figure 1: Left: Mercury’s elliptical orbit around the sun. Right: The long axis of the ellipse slowly rotates, i.e. precession of the perihelion. Source: http://archive.ncsa.illinois.edu/Cyberia/NumRel/Images/mercury.jpeg

    For centuries, astronomers used Kepler’s equations to describe the orbital motion of all the planets—with the exception of Mercury. Mercury travels in an elliptical orbit, where the orientation of the long axis of the ellipse slowly rotates (i.e. precesses) around the Sun. This is referred to as the “precession of the perihelion of Mercury”, shown in Figure 1.

    Newtonian physics does predict some precession of planetary orbits (for example, due to planets influencing each other’s orbits) but the predicted Newtonian precession does not match observations. Mercury’s peculiar behaviour remained a puzzle until Einstein’s Theory of General Relativity (GR).

    Broadly speaking, GR is a theory of gravity that describes the way massive objects distort and bend the fabric of spacetime in their neighbourhood. The more massive the object, the more spacetime will be distorted by it, so relativistic effects are seen most strongly near very massive bodies such as stars and black holes. As the closest planet to the Sun, Mercury sits in a region of spacetime that is more distorted, leading to its more irregular orbit compared to the other planets.

    Orbiting a black hole

    The measurement of the precession of the perihelion of Mercury was a transformative moment for both Einstein and modern physics. However, Mercury’s orbit can be approximated by Keplerian physics even if the exact rate of precession is not accurate. This all changes where relativistic effects are very strong—near a black hole!

    Let’s consider for a moment the motion around relativistic (i.e. extremely massive) objects such as a black hole. Imagine you are travelling in a space ship in the vicinity of a black hole. If you are far enough away, you will qualitatively orbit in pretty much the expected way: an ellipse. The fact that you are orbiting around a black hole in particular doesn’t really matter at this distance—black holes will act like any other spherical mass. Sure, the ellipse may precess, as discussed above, but nothing weirder than that.

    As you move closer to the black hole, things start to get more interesting. The two radii we are concerned with here are the Innermost Stable Circular Orbit (ISCO) and the Innermost Bound Circular Orbit (IBCO). The IBCO is typically a smaller radius than the ISCO. Traversing the IBCO will generally lead to plunging orbits (unless you have a very powerful rocket to help you escape) that take you past the event horizon. The event horizon is the point-of-no-return; once you pass the event horizon of a black hole you cannot come back out! Outside of the ISCO, we see the familiar Mercury-type precession (the precessions of an ellipse) discussed above.

    Zooming and whirling

    3
    Figure 2: Examples of orbits traced out by a test particle around a black hole, where the black hole sits at the origin. Top row: Periodic orbits around a black hole. Bottom row: Nearby aperiodic orbits. Figure 1 in paper.

    This paper focuses a lot on “zoom-whirl” behaviour, where you orbit the black hole in between the ISCO and IBCO. These complicated and intricate orbits look like patterns drawn with a spirograph (see Figure 2). A key feature of these orbits are the leaves (for example, you can trace out a four-leaf clover pattern as you orbit), which distinguishes them from Mercury-type orbits. Another interesting feature is that you can “whirl” around just outside of the IBCO essentially an unlimited number of times, and then “zoom” back out to trace along one of the leaves of the orbit. Zooms are the number of “leaves” of the orbits; whirls are number of revolutions around the IBCO before hopping back out.

    An application of periodic orbits

    Periodic orbits are special because they capture fundamental information about orbits around a black hole; all generic black hole orbits are small deviations from periodic orbits. We see examples of exactly periodic orbits and nearly periodic orbits in Figure 2. Cataloguing the periodic orbits in this way could lead to a powerful application: reducing the computational burden of gravitational wave calculations.

    Gravitational waves (which are discussed extensively in this astrobite) are ripples in spacetime generated by massive objects interacting gravitationally. For example, two black holes spiralling into each other will generate a gravitational wave signal, which we can then observe using detectors on earth such as LIGO. The authors suggest that analysis using periodic orbits may yield computational advantages. For example, it may make signal extraction from time-frequency data an easier task.

    Therefore, a periodic table of the weird and wonderful orbits around black holes is not just fundamentally fascinating, but may be useful for hunting gravitational waves.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 12:08 pm on January 5, 2017 Permalink | Reply
    Tags: , , , Black Holes, , , Super-massive black hole, Vinicius Placco   

    From Notre Dame: “Notre Dame astrophysicist confirms source of galaxy collision” 

    Notre Dame bloc

    Notre Dame University

    January 05, 2017
    Brian Wallheimer

    1
    Vinicius Placco. No image credit

    Vinicius Placco, a research assistant professor of astrophysics at Notre Dame, collaborated with colleagues at the Harvard-Smithsonian Center for Astrophysics [CfA] to confirm that a massive amount of energy seen 2 billion light years from Earth stems from the collision of two galaxy clusters at the site of a giant black hole.

    Placco’s work is published today in the inaugural edition of Nature Astronomy. The paper’s findings detail matter ejected by a black hole being swept into the merger of two galaxy clusters.

    The black hole in one galaxy cluster shoots away much of the gas flowing toward it. The fast-moving particles receive a boost of energy from the galaxy cluster collision, creating shock waves.

    Placco was able to measure the spectrum of light coming from the galaxy harboring the super-massive black hole, to prove that it belongs to the galaxy cluster pair Abell 3411-12. That was used with other data collected from NASA’s Chandra X-Ray Observatory, the Giant Metrewave Radio Telescope [GMRT] in India, and the Keck Observatory and Japan’s Subaru telescope, both on Mauna Kea, Hawaii.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    GMRT Radio Telescope, located near Pune, India
    GMRT Radio Telescope, located near Pune, India

    Keck Observatory, Mauna Kea, Hawaii, USA
    Keck Observatory, Mauna Kea, Hawaii, USA

    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA
    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA

    Placco and Rafael Santucci, a graduate student at Universidade de São Paulo, Brazil, were awarded time on the Southern Astrophysical Research (SOAR) Telescope in Chile and were making remote observations from South Bend and São Paulo. A friend from his undergraduate years at Universidade de São Paulo, Felipe Andrade-Santos, who now is a post-doctoral research fellow at Harvard, asked Placco if he would use some of his time on the telescope to observe a galaxy in the direction of the Abell 3411 and Abell 3412 galaxy clusters.

    NOAO/ Southern Astrophysical Research Telescope (SOAR)telescope situated on Cerro Pachón - IV Región - Chile, at 2,700 meters (8,775 feet)
    NOAO/ Southern Astrophysical Research Telescope (SOAR)telescope situated on Cerro Pachón – IV Región – Chile, at 2,700 meters

    “It can take six months to a year to get time on the telescope, and this would delay the research considerably. Since we were at the telescope, we could help the Harvard team confirm what they were expecting to see,” Placco said. “We were in the right place at the right time with the right expertise.”

    Placco said it is satisfying to know that he was able to help as part of one piece of a puzzle that connected researchers on several continents and countries.

    “This is what makes science interesting and appealing,” Placco said. “All of these collaborators, even though they are not in the same place all the time, they know they can count on each other and work together.”

    See the full article here .

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    Notre Dame Campus

    The University of Notre Dame du Lac (or simply Notre Dame /ˌnoʊtərˈdeɪm/ NOH-tər-DAYM) is a Catholic research university located near South Bend, Indiana, in the United States. In French, Notre Dame du Lac means “Our Lady of the Lake” and refers to the university’s patron saint, the Virgin Mary.

    The school was founded by Father Edward Sorin, CSC, who was also its first president. Today, many Holy Cross priests continue to work for the university, including as its president. It was established as an all-male institution on November 26, 1842, on land donated by the Bishop of Vincennes. The university first enrolled women undergraduates in 1972. As of 2013 about 48 percent of the student body was female.[6] Notre Dame’s Catholic character is reflected in its explicit commitment to the Catholic faith, numerous ministries funded by the school, and the architecture around campus. The university is consistently ranked one of the top universities in the United States and as a major global university.

    The university today is organized into five colleges and one professional school, and its graduate program has 15 master’s and 26 doctoral degree programs.[7][8] Over 80% of the university’s 8,000 undergraduates live on campus in one of 29 single-sex residence halls, each of which fields teams for more than a dozen intramural sports, and the university counts approximately 120,000 alumni.[9]

    The university is globally recognized for its Notre Dame School of Architecture, a faculty that teaches (pre-modernist) traditional and classical architecture and urban planning (e.g. following the principles of New Urbanism and New Classical Architecture).[10] It also awards the renowned annual Driehaus Architecture Prize.

     
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