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  • richardmitnick 12:31 pm on January 22, 2019 Permalink | Reply
    Tags: , , , , EHT - Event Horizon Telescope, , Our Galaxy's Supermassive Black Hole Could Be Pointing a Relativistic Jet Right at Us, ,   

    From Science Alert: “Our Galaxy’s Supermassive Black Hole Could Be Pointing a Relativistic Jet Right at Us” 

    ScienceAlert

    From Science Alert

    22 JAN 2019
    MICHELLE STARR

    1
    A black hole simulation (Bronzwaer/Davelaar/Moscibrodzka/Falcke/Radboud University)

    Things are officially getting exciting. New science has just come in from the collaboration to photograph Sagittarius A*, the supermassive black hole at the centre of the Milky Way, and it’s ponying up the secrets at our galaxy’s dusty heart.

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

    The image below is the best picture yet of Sgr A* (don’t worry, there’s more to come from the Event Horizon Telescope), and while it may look like just a weird blob of light to you, astrophysicists studying the radio data can learn a lot from what they’re looking at – and they think they’ve identified a relativistic jet angled towards Earth.

    EHT map

    Because the image taken of the region is the highest resolution yet – twice as high as the previous best – the researchers were able to precisely map the properties of the light around the black hole as scattered by the cloud.

    “The galactic centre is full of matter around the black hole, which acts like frosted glass that we have to look through,” astrophysicist Eduardo Ros of the Max Planck Institute for Radio Astronomy in Germany told New Scientist.

    Using very long baseline interferometry to take observations at a wavelength of 3.5 millimetres (86 GHz frequency), a team of astronomers has used computer modelling to simulate what’s inside the thick cloud of plasma, dust and gas surrounding the black hole.

    1
    Above: The bottom right image shows Sgr A* as seen in the data. The top images are simulations, while the bottom left is Sgr A* with the scattering removed.
    (S. Issaoun, M. Mościbrodzka, Radboud University/ M. D. Johnson, CfA)

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    GMVA The Global VLBI Array

    It revealed that Sgr A*’s radio emission comes from a smaller region than previously thought.

    Most of it is coming from an area just 300 milllionth of a degree of the night sky, with a symmetrical shape. And, since black holes don’t emit detectable radiation on their own, the source is most likely one of two things.

    “This may indicate that the radio emission is produced in a disk of infalling gas rather than by a radio jet,” said astrophysicist Sara Issaoun of Radboud University in The Netherlands.

    “However, that would make Sgr A* an exception compared to other radio emitting black holes. The alternative could be that the radio jet is pointing almost at us.”

    Active black holes are surrounded by a swirling cloud of material that’s falling into it like water down a drain. As this material is swallowed by the black hole, it emits jets of particles from its rotational poles at velocities approaching light speed.

    We’re not quite sure how this happens, but astronomers believe that material from the inner part of the accretion disc is channelled towards and launched from the poles via magnetic field lines.

    Since Earth is in the galactic plane, having a jet pointed in our direction would mean that the black hole is oriented quite strangely, as if it’s lying on its side. (Nearby galaxy Centaurus A, for instance, has jets shooting perpendicular to the galactic plane.)

    But this orientation has been hinted at before. Last year the GRAVITY Collaboration described flares around Sgr A* consistent with something orbiting it face-on from our perspective – like looking at the Solar System from above.

    This means the long-awaited picture of the shadow of a black hole will – hopefully – be breathtakingly detailed.

    Meanwhile, studying data such as these help build a comprehensive picture of how these mysterious cosmic objects work.

    “Understanding how black holes work … takes more than the picture of its shadow (although incredible in its own right),” Issaoun wrote on Facebook. “It takes observations at many different wavelengths (radio, X-ray, infrared etc) to piece together the entire story, so every piece counts!”

    The team’s paper has been published in The Astrophysical Journal..

    So “Maybe this is true after all,” said Radboud University astronomer Heino Falcke, “and we are looking at this beast from a very special vantage point.”

    Hopefully, when the Event Horizon Telescope releases the first images of Sgr A*’s event horizon – something we are expecting very soon – they will reveal more. And, in case you were starting to get worried, the 1.4-millimetre wavelength (230 GHz) will reduce the light scattering by a factor of 8.

    See the full article here .

    See also here .


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  • richardmitnick 12:15 pm on December 23, 2018 Permalink | Reply
    Tags: , , , , , EHT - Event Horizon Telescope, , New fellowships, ,   

    From Perimeter Institute: “New fellowships to fuel fundamental physics with radio telescopes in Canada” 

    Perimeter Institute

    From Perimeter Institute

    December 20, 2018

    Perimeter Institute and Canada’s National Research Council have created a pair of postdoctoral fellowships for exceptional emerging radio astronomers.

    As radio astronomy enters a transformative new era, Perimeter Institute and Canada’s National Research Council (NRC) have launched two new fellowships to accelerate the research of young scientists conducting theory, data analysis, or instrument development.

    The new initiative is a collaboration between Perimeter and NRC’s Dominion Radio Astrophysical Observatory (DRAO), the site of Canada’s revolutionary Canadian Hydrogen Intensity Mapping Experiment (CHIME) Telescope.

    CHIME Canadian Hydrogen Intensity Mapping Experiment -A partnership between the University of British Columbia, the University of Toronto, McGill University, Yale and the National Research Council in British Columbia, at the Dominion Radio Astrophysical Observatory in Penticton,British Columbia

    Instruments like CHIME and forthcoming experiments possess unprecedented statistical power, promising to open new windows into fundamental physics questions, including dark matter, gravity, and neutrinos. These instruments will be used to tackle new challenges in data analysis and high-performance computing, and will help scientists resolve deep astronomical puzzles, such as the origin of fast radio bursts (FRBs).

    The Perimeter-DRAO partnership will bring together theorists, data analysts, and instrumentalists at the leading edge of this very exciting field.

    One of the postdoctoral fellows will be based at the DRAO, with the other at Perimeter Institute; each will be encouraged to spend time at the other institution to deepen the partnership and strengthen the connections between the institutions.

    Perimeter Institute is part of a number of radio astronomy collaborations, including CHIME/FRB, HIRAX (Hydrogen Intensity and Real-time Analysis Experiment), and the EHT (Event Horizon Telescope), among others.

    SKA HIRAX prototype dishes at Hartebeesthoek Astronomy Observatory near Johannesburg.

    EHT map

    EHT APEX, IRAM, G. Narayanan, J. McMahon, JCMT/JAC, S. Hostler, D. Harvey, ESO/C. Malin

    Perimeter researchers associated with these initiatives include Avery Broderick, Ue-Li Pen, Will Percival, Daniel Siegel, Kendrick Smith, and Neil Turok.

    In addition to hosting CHIME in British Columbia and several other radio telescopes, DRAO features laboratories and specialized equipment for the design and construction of all aspects of radio-frequency instrumentation, from highly sensitive antennae and receiver systems to high-speed digital signal processing hardware and software. This national facility is home to astronomers, astrophysicists, engineers, and technologists, as well as visiting researchers and students from universities and astronomical observatories around the world.

    The deadline to apply for the fellowships is January 31, 2019. Find more information and apply here.

    See the full article here .


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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 2:23 pm on October 21, 2018 Permalink | Reply
    Tags: Are Black Holes Actually Dark Energy Stars?, , , , , EHT - Event Horizon Telescope,   

    From Nautilus: “Are Black Holes Actually Dark Energy Stars?” 

    Nautilus

    From Nautilus

    Oct 15, 2018
    Jesse Stone

    1
    George Chapline believes that the Event Horizon Telescope will offer evidence that black holes are really dark energy stars. NASA.

    What does the supermassive black hole at the center of the Milky Way look like? Early next year, we might find out. The Event Horizon Telescope—really a virtual telescope with an effective diameter of the Earth—has been pointing at Sagittarius A* for the last several years.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    NSF CfA Greenland telescope

    Greenland Telescope

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    Most researchers in the astrophysics community expect that its images, taken from telescopes all over the Earth, will show the telltale signs of a black hole: a bright swirl of light, produced by a disc of gases trapped in the black hole’s orbit, surrounding a black shadow at the center—the event horizon. This encloses the region of space where the black-hole singularity’s gravitational pull is too strong for light to escape.

    But George Chapline, a physicist at the Lawrence Livermore National Laboratory, doesn’t expect to see a black hole. He doesn’t believe they’re real. In 2005, he told Nature that “it’s a near certainty that black holes don’t exist” and—building on previous work he’d done with physics Nobel laureate Robert Laughlin—introduced an alternative model that he dubbed “dark energy stars.” Dark energy is a term physicists use to describe a peculiar kind of energy that appears to permeate the entire universe.

    Dark energy depiction. Image: Volker Springle/Max Planck Institute for Astrophysics/SP)

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    It expands the fabric of spacetime itself, even as gravity attempts to bring objects closer together. Chapline believes that the immense energies in a collapsing star cause its protons and neutrons to decay into a gas of photons and other elementary particles, along with what he refers to as “droplets of vacuum energy.” These form a “condensed” phase of spacetime—much like a gas under enough pressure transitions to liquid—that has a much higher density of dark energy than the spacetime surrounding the star. This provides the pressure necessary to hold gravity at bay and prevent a singularity from forming. Without a singularity in spacetime, there is no black hole.

    The idea has found no support in the astrophysical community—over the last decade, Chapline’s papers on this topic have garnered only single-digit citations. His most popular paper in particle physics, by contrast, has been cited over 600 times. But Chapline suspects his days of wandering in the scientific wilderness may soon be over. He believes that the Event Horizon Telescope will offer evidence that dark energy stars are real.

    The idea goes back to a 2000 paper [International Journal of Modern Physics A], with Evan Hohlfeld and David Santiago, in which Chapline and Laughlin modeled spacetime as a Bose-Einstein condensate—a state of matter that arises when taking an extremely low-density gas to extremely low temperatures, near absolute zero. Chapline and Laughlin’s model is quantum mechanical in nature: General relativity emerges as a consequence of the way that the spacetime condensate behaves on large scales. Spacetime in this model also undergoes phase transformations when it gains or loses energy. Other scientists find this to be a promising path, too. A 2009 paper [Physical Review A] by a group of Japanese physicists stated that “[Bose-Einstein Condensates] are one of the most promising quantum fluids for” analogizing curved spacetime.

    Chapline and Laughlin argue that they can describe the collapsed stars that most scientists take to be black holes as regions where spacetime has undergone a phase transition. They find that the laws of general relativity are valid everywhere in the vicinity of the collapsed star, except at the event horizon, which marks the boundary between two different phases of spacetime.

    In the condensate model the event horizon surrounding a collapsed star is no longer a point of no return but instead a traversable, physical surface. This feature, along with the lack of a singularity that is the signature feature of black holes, means that paradoxes associated with black holes, like the destruction of information, don’t arise. Laughlin has been reticent to conjecture too far beyond his and Chapline’s initial ideas. He believes Chapline is onto something with dark energy stars, “but where we part company is in the amount of speculating we are willing to do about what ‘phase’ of the vacuum might be inside” what most scientists call black holes, Laughlin said. He’s holding off until experimental data reveals more about the interior phase. “I will then write my second paper on the subject,” he said.

    In recent years Chapline has continued to refine his dark energy star model in collaboration with several other authors, including Pawel Mazur of the University of South Carolina and Piotr Marecki of Leipzig University. He’s concluded that dark energy stars aren’t spherical or oblate, like black holes. Instead, they have the shape of a torus, or donut. In a rotating compact object, like a dark energy star, Chapline believes quantum effects in the spacetime condensate generate a large vortex along the object’s axis of rotation. Because the region inside the vortex is empty—think of the depression that forms at the center of whirlpool—the center of the dark energy star is hollow, like an apple without its core. A similar effect is observed when quantum mechanics is used to model rotating drops of superfluid. There too, a central vortex can form at the center of a rotating drop and, surprisingly, change its shape from a sphere to a torus.

    For Chapline, this strange toroidal geometry isn’t a bug of dark energy stars, but a feature, as it helps explain the origin and shape of astrophysical jets—the highly energetic beams of ionized matter that are generated along the axis of rotation of a compact object like a black hole. Chapline believes he’s identified a mechanism in dark energy stars that explains observations of astrophysical jets better than mainstream ones, which posit that energy is extracted from the accretion disk outside of a black hole and focused into a narrow beam along the black hole’s axis of rotation. To Chapline, matter and energy falling toward a dark energy star would make its way to the inner throat (the “donut hole”), where electrons orbiting the throat would, as in a Biermann Battery, generate magnetic fields powerful enough to drive the jets.

    Chapline points to recent experimental work where scientists, at the OMEGA Laser Facility at the University of Rochester, created magnetized jets using lasers to form a ring-like excitation on a flat surface.

    U Rochester Omega Laser facility

    Though the experiments were not conducted with dark energy stars in mind, Chapline believes it provides support for his theory since the ring-like excitation—Chapline calls it a “ring of fire”—is exactly what he would expect to happen along the throat of a dark energy star. He believes the ring could be the key to supporting the existence of dark energy stars. “This ought to eventually show up clearly” in the Event Horizon Telescope images, Chapline said, referring to the ring.

    3
    Black hole vs dark energy star: When viewed from the top down, a dark energy star has a central opening, the donut hole. Chapline believes that matter and energy rotating around the central opening (forming the “ring of fire”) is the source of the astrophysical jets observed by astronomers in the vicinity of what most believe to be black holes. No image credit.

    Chapline also points out that dark energy stars will not be completely opaque to light, as matter and light can pass into, but also out of, a dark energy star. A dark energy star won’t have a completely black interior—instead it will show a distorted image of any stars behind it. Other physicists, though, are skeptical that these kinds of deviations from conventional black hole models would show up in the Event Horizon Telescope data. Raul Carballo-Rubio, a physicist at the International School for Advanced Studies, in Trieste, Italy, has developed his own alternative model to black holes known as semi-classical relativistic stars. Speaking more generally about alternative black hole models Caraballo-Rubio said, “The differences [with black holes] that would arise in these models are too minute to be detected” by the Event Horizon Telescope.

    Chapline plans to discuss his dark energy star predictions in December, at the Kavli Institute for Theoretical Physics in Santa Barbara. But even if his predictions are confirmed, he said he doesn’t expect the scientific community to become convinced overnight. “I expect that for the next few years the [Event Horizon Telescope] people will be confused by what they see.”

    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 10:06 am on October 11, 2018 Permalink | Reply
    Tags: , , , , EHT - Event Horizon Telescope, , , This Is How We Will Successfully Image A Black Hole’s Event Horizon   

    From Ethan Siegel: “This Is How We Will Successfully Image A Black Hole’s Event Horizon” 

    From Ethan Siegel
    Oct 10, 2018

    1
    Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole’s accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results. (GRMHD SIMULATIONS OF VISIBILITY AMPLITUDE VARIABILITY FOR EVENT HORIZON TELESCOPE IMAGES OF SGR A*, L. MEDEIROS ET AL., ARXIV:1601.06799)

    As the Event Horizon Telescope prepares to release its first results, we can expect not just one, but two black hole images.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    NSF CfA Greenland telescope

    Greenland Telescope

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    What does a black hole actually look like? For generations, scientists argued over whether black holes actually existed or not. Sure, there were mathematical solutions in General Relativity that indicated they were possible, but not every mathematical solution corresponds to our physical reality. It took observational evidence to settle that issue.

    Owing to matter orbiting and infalling around black holes, both stellar-mass versions and the supermassive versions, we’ve detected the X-ray emissions characteristic of their existences. We found and measured the motions of individual stars that orbit suspected black holes, confirming the existence of massive objects at the centers of galaxies. If only we could directly image these objects that emit no light themselves, right? Amazingly, that time is here.

    2
    The black hole at the center of the Milky Way, along with the actual, physical size of the Event Horizon pictured in white. The visual extent of darkness will appear to be 5/2 as large as the event horizon itself.(UTE KRAUS, PHYSICS EDUCATION GROUP KRAUS, UNIVERSITÄT HILDESHEIM; BACKGROUND: AXEL MELLINGER)

    In theory, a black hole is an object that cannot hold itself up against gravity. Whatever outward forces there are — including radiation, nuclear and electromagnetic forces, or even quantum degeneracy arising from the Pauli exclusion principle — must be equal and opposite to the inward force of gravity, or collapse is inevitable. If you get that gravitational collapse, you will form an event horizon.

    An event horizon is the location where the fastest speed attainable, the speed of light, is exactly equal to the speed necessary to escape from the gravity of the object inside. Outside of the event horizon, light can escape. Inside the event horizon, light cannot. It’s for this reason that black holes are expected to be black: the event horizon should describe a dark sphere in space where there should be no light detectable of any type.

    We see objects in the Universe that are so consistent with the expectations for a black hole that there are no good theories, at all, for what else they might be. Furthermore, we can calculate how large these event horizons should both physically be for a black hole (proportional to a black hole’s mass) and how large they should appear in General Relativity (about 2.5 times the diameter of the physical extent).

    As viewed from Earth, the largest apparent black hole should be Sagittarius A*, which is the black hole at the center of the Milky Way, with an apparent size of approximately 37 micro-arc-seconds. At 4 million solar masses and a distance of around 27,000 light years, it should appear larger than any other. But the second largest one? That’s at the center of Messier 87, over 50 million light years away.

    SgrA* NASA/Chandra


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

    3
    The second-largest black hole as seen from Earth, the one at the center of the galaxy Messier 87, is shown in three views here. Despite its mass of 6.6 billion Suns, it is over 2000 times farther away than Sagittarius A*. It may not be resolvable by the EHT if our mass estimates are too large, but if the Universe is kind, we’ll get an image, after all. (TOP, OPTICAL, HUBBLE SPACE TELESCOPE / NASA / WIKISKY; LOWER LEFT, RADIO, NRAO / VERY LARGE ARRAY (VLA); LOWER RIGHT, X-RAY, NASA / CHANDRA X-RAY TELESCOPE)

    NASA/ESA Hubble Telescope

    NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    NASA/Chandra X-ray Telescope

    The reason that black hole is so huge? Because even at that incredible distance, it’s over 6 billion solar masses, meaning it should appear as roughly 3/4ths the size of the Milky Way’s black hole. Black holes are well-known for emitting radiation in the radio portion of the spectrum, as matter accelerates around the event horizon, but this gives us a brilliant way to attempt to view it: through very-long-baseline interferometry in the radio portion of the spectrum.

    All we need, to make that happen, is an enormous array of radio telescopes. We need them all over the globe, so that we can take temporally simultaneous measurements of the same objects from locations up to 12,700 kilometers (8,000 miles) away: the diameter of Earth. By taking these multiple images, we can piece together an image — so long as the source we’re imaging is radio-bright enough — as small as 15 micro-arc-seconds in size.

    The Event Horizon Telescope (EHT) is exactly such an array, and it’s not only been taking data from all over the world (including in Antarctica) for years, it’s already taken all the images necessary of Sagittarius A* and of Messier 87 you could hope for. All that’s left, now, is to process the data and construct the images for the general public to view.

    4
    Two of the possible models that can successfully fit the Event Horizon Telescope data thus far, as of earlier in 2018. Both show an off-center, asymmetric event horizon that’s enlarged versus the Schwarzschild radius, consistent with the predictions of Einstein’s General Relativity. (R.-S. LU ET AL, APJ 859, 1)

    We’ve already taken the data necessary to create the first black hole images ever, so what’s the hold up? What are we poised to learn? And what might surprise us about what the Universe has in store?

    In theory, the event horizon should appear as an opaque black circle, letting no light from behind it through. It should display a brightening on one side, as matter accelerates around the black hole. It should appear 250% the size that General Relativity predicts, due to the distortion of spacetime. And it should happen because of a spectacular network of telescopes, in unison, all viewing the same object.

    5
    The Allen Telescope Array is potential capable of detecting a strong radio signal from Proxima b, or of working in concert with other radio telescopes across extremely long baselines to try and resolve the event horizon of a black hole. (WIKIMEDIA COMMONS / COLBY GUTIERREZ-KRAYBILL)

    Normally, the resolution of your telescope is determined by two factors: the diameter of your telescope and the wavelength of light you’re using to view it. The number of wavelengths of light that fit across your dish determines the optimal angular diameter you can resolve. Yet if this were truly our limits, we’d never see a black hole at all. You’d need a telescope the diameter of the Earth to view even the closest ones in the radio, where black holes emit the strongest and most reliably.

    But the trick of very-long baseline interferometry is to view extremely bright sources, simultaneously, from identical telescopes separated by large distances. While they only have the light-gathering power of the surface area of the individual dishes, they can, if a source is bright enough, resolve objects with the resolution of the entire baseline. For the Event Horizon Telescope, that baseline is the diameter of the Earth.

    I’m so pleased that the Event Horizon Telescope, and imaging the event horizon of a black hole directly, was the topic of October 3rd’s Perimeter Institute public lecture: Images from the Edge of Spacetime, by Avery Broderick.

    The live blog is now complete, having aired initially at 7 PM Eastern Time (4 PM Pacific Time), and you can follow along by watching the video below. Watch the talk any time, and follow along with the live blog that follows!

    (All updates, below, will have the timestamps in bold in Pacific time, with screenshots where appropriate from the lecture itself.)


    1:26:25
    3:50 PM: Welcome! Let’s start the Live Blog a little early, so we can give you a bit of background.

    The biggest thing you have to realize, when it comes to imaging a black hole’s event horizon, is that we’re not looking for light, but the absence of light. When you look at a galaxy’s center, you’re going to see a ton of light, coming from all the matter located there. What the event horizon of a black hole gives you, spectacularly, is a shadow: a region wherein any light coming from behind it gets absorbed and swallowed. The key to imaging the event horizon is to see the light, behind the black hole, that emerges from around the horizon itself.

    7
    Some of the possible profile signals of the black hole’s event horizon as simulations of the Event Horizon Telescope indicate. (HIGH-ANGULAR-RESOLUTION AND HIGH-SENSITIVITY SCIENCE ENABLED BY BEAMFORMED ALMA, V. FISH ET AL., ARXIV:1309.3519)

    3:54 PM: What’s an incredibly exciting possibility, that hopefully we’ll get to hear more about in this lecture, is what we might see if something is flawed in Einstein’s theory of general relativity. Of course we expect Einstein to be right; general relativity has never led us astray yet, not in any experiment, measurement, or at any level of detail. But if the event horizon is a different size, opacity, or shape than what we predict, or doesn’t even exist at all, that could lead us to a revolution in physics. Quantum gravitational effects, for example, shouldn’t be important here. But if they are… well, that’s part of why we look!

    8
    This multiwavelength view of the Milky Way’s galactic center goes from the X-ray through the optical and into the infrared, showcasing Sagittarius A* and the intragalactic medium located some 25,000 light years away. Using radio data, the EHT will resolve the black hole’s event horizon. (X-RAY: NASA/CXC/UMASS/D. WANG ET AL.; OPTICAL: NASA/ESA/STSCI/D.WANG ET AL.; IR: NASA/JPL-CALTECH/SSC/S.STOLOVY)

    3:58 PM: I know we’re all hoping for an answer to the biggest question we have: what does the event horizon look like? That’s why we have the telescope array, after all, doing what it’s doing. But take a look at the multiwavelength image above. We have to see through all of that radiation, and prevent it from being a foreground contaminant, to image the event horizon of the black hole itself.

    It’s important to appreciate how much of the Universe we have to see through, as though it were transparent (and it’s not 100% transparent), just to have a shot at the event horizon itself. Today, I’m hoping we learn exactly how we can do this, and why we’re so confident that the EHT will get us there. Remember, the Milky Way’s black hole, and all black holes, are radio-loud objects!

    9
    This four-panel view shows the Milky Way’s central region in four different wavelengths of light, with the longer (submillimeter) wavelengths at top, going through the far-and-near infrared (2nd and 3rd) and ending in a visible-light view of the Milky Way. Note that the dust lanes and foreground stars obscure the center in visible light, but not so much in the infrared. (ESO/ATLASGAL CONSORTIUM/NASA/GLIMPSE CONSORTIUM/VVV SURVEY/ESA/PLANCK/D. MINNITI/S. GUISARD ACKNOWLEDGEMENT: IGNACIO TOLEDO, MARTIN KORNMESSER)

    4:01 PM: Before the lecture starts, and it’s about to begin, here’s one last thing: this is the center of the Milky Way in four independent wavelengths. There’s a lot going on there, and we’re looking for an object that’s roughly the size of Jupiter’s orbit around the Sun. Are you not impressed at the ambition of the EHT? You should be impressed!!

    4:04 PM: If you’re wondering why we don’t go for a closer black hole than the Milky Way’s center, because there are closer ones, it’s because the size of a black hole is dependent on its mass and its distance. Double the mass means double the radius; double the distance means half the radius. The second most massive black hole in the Milky Way that we’ve ever found is thousands of times less massive than the one at our galaxy’s center, but only about 10–20 times closer. This is why we go for bigger rather than closer!

    10
    Hawking radiation is what inevitably results from the predictions of quantum physics in the curved spacetime surrounding a black hole’s event horizon. This visualization is more accurate than a simple particle-antiparticle pair analogy, since it shows photons as the primary source of radiation rather than particles. However, the emission is due to the curvature of space, not the individual particles, and doesn’t all trace back to the event horizon itself. (E. SIEGEL)

    4:08 PM: “Black holes are objects into which things go, and don’t come out.” That is a solid definition of a black hole, which Avery gave… to first order. This should be true for every black hole in our Universe, but give it time. After about 10²⁰ years, perhaps a billion (or ten) times the age of our Universe, they’ll start to radiate, via Hawking radiation, faster than it can absorb any matter that surrounds it. They will shrink, and when they do, that will herald their disappearance.

    On long enough timescales, things will come out, albeit not from inside the black hole, but from the curved spacetime outside of it.

    4:10 PM: Avery says if you crush the Sun down to 3 km, it would become a black hole. Crush the Earth to 1 cm, and it’s a black hole. Crush a human, and it’s about 10^-11 times the width of a proton. (This is a correction to Avery’s number.)

    And crush the Universe down to… approximately the size of the Universe itself, and it’ll be a black hole? Be careful here; the Universe is expanding, and full of dark energy, and that changes the equation tremendously. Our Schwarzschild solution, a great approximation for real black holes, no longer applies here. (I hope Avery gets this right when he gets there!)

    11
    Our galaxy’s supermassive black hole has witnessed some incredibly bright flares, but none was as bright or long-lasting as XJ1500+0134. Owing to events like this and many others, a large amount of Chandra data, over a 19 year time period, exists of the galactic center. (NASA/CXC/STANFORD/I. ZHURAVLEVA ET AL.)

    4:14 PM: Looking at supermassive black holes is fantastic; you get to see, in the radio, these massive lobes.

    But the image above, that I’ve chosen, is in the X-ray! Black holes are powerful all across the electromagnetic spectrum. We can see their effects because, as Avery correctly notes, the matter expelled from the black holes changes their environments.

    4:17 PM: Avery makes the point that the Universe is complicated, but black holes are simple. And this is true, so long as you’re looking at their macro-properties. But there is a huge amount of theoretical motivation to assume that what a black hole is made out of matters! If you made a black hole out of 10⁵⁵ neutrons or 10⁵⁵ antineutrons, there should be a difference. Not in General Relativity, but in terms of information and quantum numbers.

    Does this actually matter? We’re not sure, and the EHT won’t teach us that. There are many questions we ought to remember that physics has left to resolve, no matter what the answers the EHT (or any experiment) can give us.

    4:20 PM: Avery brings up a fun acronym: ISCO. ISCO stands for innermost stable circular orbit. This is not the event horizon, but rather an orbit about three times the radius of the event horizon. There should be, therefore, an empty hole that’s in between ISCO and the event horizon, where no matter (stably) exists.

    The innermost orbit for matter, and for photons, and for even the spacetime that starts to get dragged around (yes, this happens!), all affect what someone viewing the event horizon would actually see. Frame-dragging is a real effect in relativity, and cannot be ignored!

    12
    Countless scientific tests of Einstein’s general theory of relativity have been performed, subjecting the idea to some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around a single mass, like the Sun; he applied these results to our Solar System with dramatic success. We can view this orbit as Earth (or any planet) being in free-fall around the Sun, traveling in a straight-line path in its own frame of reference. (LIGO SCIENTIFIC COLLABORATION / T. PYLE / CALTECH / MIT)

    4:24 PM: I think this is a really important point that Avery only glosses over, but is a source of confusion for a lot of people in General Relativity. The curvature of spacetime is not determined by mass. Sure, no less a figure than Wheeler noted that matter tells spacetime how to curve; curved space tells matter how to move, but it’s more than that. The curvature of spacetime is determined by the presence, distribution, and density of both matter and energy. This includes energy of all forms: radiation, kinetic energy, and many quantities other than just mass.

    Mass plays a major role, but it isn’t the only important thing as far as affecting spacetime goes.

    13
    A large slew of stars have been detected near the supermassive black hole at the Milky Way’s core. In addition to these stars and the gas and dust we find, we anticipate there to be upwards of 10,000 black holes within just a few light years of Sagittarius A*, but detecting them had proved elusive until now. (S. SAKAI / A. GHEZ / W.M. KECK OBSERVATORY / UCLA GALACTIC CENTER GROUP)

    4:27 PM: I want to note something that Avery said at the 0:25 minute mark in his talk, asking if these objects with large masses and X-ray/radio emissions are, in fact, black holes? He then left the question hanging and didn’t answer.

    But you know what? Except for crackpots on the internet, pretty much everyone now accepts that these objects are black holes, and it was Andrea Ghez’s group, at UCLA, that answered that question for us. You see stars, by looking in the infrared, orbiting a point of incredible mass, about 4 million solar masses. Yet no light (at least, in the infrared) comes from that mass.

    Why? Because there is no explanation for it other than a black hole. That’s a black hole, folks, and with supreme confidence we can look for it with a telescope like the EHT.

    14
    The galaxy NGC 1277, speeding through the Perseus cluster, not only contains predominantly red stars, but red (and not blue) globular clusters, as well as a shockingly large supermassive black hole to go along with its rapid speed through the cluster. (MICHAEL A. BEASLEY, IGNACIO TRUJILLO, RYAN LEAMAN & MIREIA MONTES, NATURE (2018), DOI:10.1038/NATURE25756)

    4:31 PM: There is a great graphic and a great conundrum in Avery’s talk. The largest black hole, as seen from Earth, is the one at the Milky Way’s center. The second largest is the one at M87. The fourth largest? The one at the center of Andromeda.

    But the third largest is a weirdo: NGC 1277. It’s the size of the Milky Way, but appears to have a >10 billion solar mass black hole. This is controversial, but it’s a tantalizing possibility!

    4:34 PM: Why is it so hard to resolve a black hole? Well, many reasons. We talked about resolution earlier, but that’s not the only one.

    Not every galaxy is radio-loud, meaning you can’t see the shadow against the radio background if there is no background. (And so, sorry NGC 1277 fans, that’s out.) If a galaxy isn’t radio-transparent, because there’s too much foreground, it won’t be visible either. But if you’re limited by diffraction, which is the nature of your telescope, you can see the wavelength divided by your telescope’s diameter. You’d need a ~12 million meter diameter telescope to get the EHT’s resolution in the radio.

    4:38 PM: So why does Avery, at the 0:36 mark in his talk, say you’d need a 5 km telescope, rather than a 12 million meter telescope, to see the black hole at the galaxy’s center?

    Two reasons. Number one, the telescopes he’s talking about are optical/infrared, which have wavelengths that are around 1,000 times shorter than the radio wavelengths the EHT will look at. (This is good; the plane of the Milky Way, which includes the galactic center, is opaque to visible light!)

    Number two, you want better resolution than the thing you’re trying to image. Otherwise, it’s just one pixel, and you can’t learn what you want to learn about an event horizon from just one pixel!

    14
    The occultation of Jupiter’s moon, Io, with its erupting volcanoes Loki and Pele, as occulted by Europa, which is invisible in this infrared image. GMT will provide significantly enhanced resolution and imaging. (LBTO)

    4:45 PM: His analogy with Fourier series isn’t really doing it for me. If you wonder, “how can you use multiple telescopes to get the resolution I need” to reconstruct an image, it is highly dependent on what you’re looking at. Always, more telescopes covering more area at more locations are better.

    But if you only have two telescopes, you can still do incredible thing, like the Large Binocular Telescope Observatory (LBTO) did just a few years ago, when they imaged erupting volcanoes on Jupiter’s Moon, Io, while another of its moons (Europa) eclipsed it. Pretty incredible!

    15
    The amount of computational power and data-writing speed has been the limiting factor in EHT-like studies. Proto-EHT began in 2007, and was capable of doing absolutely none of the science it’s doing today. (PERIMETER INSTITUTE)

    4:49 PM: So what took us so long to build the EHT? After all, we’ve had telescopes and planet Earth for a really, really long time, and we’ve been capable of taking these images. But it requires a whole lot of data. Writing down enough (and the right kinds of) data, fast enough, and then bringing them together with enough computational power to analyze them, is only now, for the first time, possible. If we had tried even a decade ago to build and run the EHT, it would not have been possible.

    4:51 PM: Avery says the biggest advance was the addition of ALMA to the EHT array. And ALMA is so, so fantastic. A piece of the array is shown, above, but check out below, where ALMA has taken some pretty spectacular, high-resolution images of… well, planets forming around young stars, like nothing else ever has, even up through today.

    4:53 PM: And now, at last, at the 0:51 minute mark of the talk, we get the real reason why all this analysis takes so long. There are different atmospheric phase delays that include calibration, calculation, mistakes and re-calculation, of 27 Petabytes of data, from all the different stations.

    Computational time is often a joke, but that’s the hold up. He has no images to show, because there are no final-version, mistake-free images available. Early 2019, maybe, is what he says we can look forward to for the first images.

    4:54 PM: Be patient, EHT fans! Be pleased they are taking the time to get it right!

    4:58 PM: Avery has just made an argument for why black holes must exist, and the objects at the centers of the Milky Way and M87 must be one. (Or, two, more accurately.) If you have stuff that falls onto a central accreting body, it will heat up and shine. But if they run into a hard object that doesn’t have an event horizon, it will heat up and shine upon impact. If you had impact emission, it would show up.

    There was no emission, which should theoretically show up in the infrared. The lack of this would push above the infrared limits, and it’s not there!

    Bam!

    And therefore, black hole. It can’t be large and cool, and isn’t hot enough to be a non-black-hole. QED.

    15
    The second-largest black hole as seen from Earth, the one at the center of the galaxy Messier 87, is around 1000 times larger than the Milky Way’s black hole, but is over 2000 times farther away. The relativistic jet emanating from its central core is one of the largest, most collimated ones ever observed. (ESA/HUBBLE AND NASA)

    5:02 PM: So how do you measure the mass of a black hole? You measure the gas orbiting the central black hole; you measure the stars orbiting it. But you get two different numbers, and they disagree. They disagree by about a factor of 2 for M87, and (although most people don’t remember) they used to disagree for the Milky Way in the early 2000s. From X-rays, we estimated around 2.5–2.7 million solar masses, but from stars, we estimate 4 million solar masses.

    Who’s right? My bet is on stars because the observations have fewer assumptions to translate into a mass, but the EHT should teach us which (if either) is correct!

    5:04 PM: Avery contends these are the two black holes you’d want, ideally, to test black holes. They’re different; one is small and close, the other is large and farther; one is active with a big jet (M87) while the other is quiet; both have a large enough angular size to be resolved with a telescope the size of our planet, etc. And these are good arguments. But I’d still rather have a stellar mass black hole that happened to be within just a few light years to try out. Any help, Alpha Centauri?

    (This is the first Perimeter talk I’ve seen that hasn’t been properly budgeted for time, BTW, so I’m sorry if any of you watching are bummed that it’s gone over.)

    16
    The proto-EHT data is consistent with, but only weakly constrains, the black hole properties of our galaxy’s center. (PERIMETER INSTITUTE)

    5:08 PM: Avery is talking about the early proto-EHT data, that took these first observations, and showed it was consistent with our models of black holes within General Relativity. But there is really so little that we get; we get info about mass, a little bit about rotation, and a little bit about the surrounding environment. Until we can see the horizon itself, and know its shape, we are very limited in what we can constrain.

    Even Avery is disappointed with what we can say with Proto-EHT data.

    5:10 PM: What will be very, very cool, that Avery is telling, is that there will be movies, not just images, that are interesting. On timescales of decades, black holes will jitter, similar to how Brownian motion works. Atoms and molecules bounce off of tiny particles under a microscope; that’s Brownian motion. Well, for the black hole at the galactic center, stars orbit and move closer-or-farther from the central black hole, and they gravitationally push it around!

    5:12 PM: I would like to point out that this is why it’s so important to make your observations simultaneously in time to one another; you cannot reconstruct a single image from interferometry if you’re not looking at the same object anymore. Like Heraclitus said, “you can’t step into the same river twice.” Well, you can’t look at the same black hole twice, apparently.

    That’s deep.

    5:13 PM: Okay, for those of you watching, I’m just going to say that if you’re 73 minutes into a 60 minute talk, and you’re just now mentioning things like the “Bardeen-Petterson effect,” someone should start playing the “wrap-it-up” music.

    17
    The supermassive black hole at the center of our galaxy, Sagittarius A*, flares brightly in X-rays whenever matter is devoured. In other wavelengths of light, from infrared to radio, we can see the individual stars in this innermost portion of the galaxy. (X-RAY: NASA/UMASS/D.WANG ET AL., IR: NASA/STSCI)

    5:17 PM: Okay, this last thing is cool enough that I should mention here: flares at the center of the Milky Way’s black hole. They happen, and they typically last minutes.

    But why? Are they turbulent features in the accretion disk? Or are they arising from the infall of matter, like “hot blobs” in the accretion flow, that flare out when they get accelerated and devoured?

    Models of both are continuously being improved, and based not on the event horizon itself, but the luminous signals that come out around the outside of the event horizon, we might be able to tell them apart. Why does our black hole flare? The EHT might teach us.

    5:20 PM: So, if you’ve made it this far, you probably watched the whole thing. So how do you sum it up?

    Black holes are real.
    We can see their effects and learn about it indirectly.
    They should have event horizons.
    The EHT should create an image of them with the data we have.
    It will take lots of time.
    And if we observe the light from outside of them, we might learn more about the environment of these black holes, and what causes transient events like flares.

    And that’s the end! Q&A time!

    5:22 PM: Fun question: what gets ejected from a black hole? What are these jets made out of? Where do they come from?

    Avery gives the real answer: we don’t know. We think they’re filled with protons, nuclei, etc., and that’s Avery’s first answer. But they could be just electromagnetic (light) radiation. (Avery says that; most scientists, as I understand it, deem that incredibly unlikely.)

    The follow-up is what is the jet’s effect on the black hole? While Avery is assuming equal-and-opposite bipolar jets, that assumption isn’t necessary. It’s like asking what effect a fly has as it splats on your semi truck’s windshield. It’s negligible.

    5:25 PM: Avery’s final question is what made him want to study black holes? And the answer is… Star Trek! There’s no better way to end a live-blog than that, so live long and prosper, everyone, and I’ll see you next time!

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

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

     
  • richardmitnick 8:22 pm on September 24, 2018 Permalink | Reply
    Tags: , , , , , EHT - Event Horizon Telescope, Planning for Images of a Black Hole   

    From AAS NOVA: “Planning for Images of a Black Hole” 

    AASNOVA

    From AAS NOVA

    24 September 2018
    Susanna Kohler

    1
    Some example snapshots of the simulated shadow of the event horizon of a black hole. The images from this simulation demonstrate what we expect to see in 1.3-mm emission in eventual images from the Event Horizon Telescope. [Adapted from Medeiros et al. 2018]

    In 2006 an ambitious project was begun: creating the world’s largest telescope with the goal of imaging the shadow of a black hole. But how will we analyze the images this project produces?

    A Planet-Sized Telescope

    Event Horizon Telescope Array

    The locations of the participating telescopes of the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) as of March 2017. Jointly, these telescopes plan to image the shadow of the event horizon of the supermassive black hole at the center of the Milky Way. [ESO/O. Furtak]

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    NSF CfA Greenland telescope

    Greenland Telescope

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    The Event Horizon Telescope (EHT) is composed of radio observatories around the world. These observatories combine their data using very-long-baseline interferometry to create a virtual telescope that has an effective diameter of the entire planet!

    The EHT, researchers hope, will have the power to peer in millimeter emission down to the very horizon of an accreting black hole — specifically, Sgr A*, the supermassive black hole in the Milky Way’s center — to learn about black-hole physics and general relativity in the depths of this monster’s gravitational pull.

    Today, the EHT is closer than ever to its goal, as the project continues to increase its resolving power and sensitivity as more telescopes join the system. Another important aspect of this project exists, however: the ability to analyze and characterize the images it produces in a meaningful way.

    3
    A simple example of using principal component analysis to decompose a set of images into independent eigenimages. The example images (top row) are snapshots from a simple model of a Gaussian spot moving on a circular path. The first four components of the principal component analysis decomposition — the four leading eigenimages — are shown in the bottom row, labeled with their corresponding eigenvalues. [Adapted from Medeiros et al. 2018]

    Recently, a team of scientists led by Lia Medeiros (University of Arizona, University of California Santa Barbara) has demonstrated that a novel approach — principal component analysis — may be a useful tool in this process.

    Principal Components

    Principal component analysis is a clever mathematical approach that allows the user to convert a complicated set of observations of variables into their “principal components”. This process — commonly used in traditional statistical applications like economics and finance — can simplify the amount of information present in the observations and help identify variability.

    Medeiros and collaborators demonstrate that a time sequence of simulated EHT observations — produced from high-fidelity general-relativistic magnetohydrodynamic simulations of a black hole — can be decomposed using principal component analysis into a sum of independent “eigenimages”. These eigenimages provide a means of compressing the information in the snapshots: most snapshots can be reproduced by summing just a few dozen of the leading eigenimages.

    Exploring Steady and Variable Flow

    4
    A typical snapshot from a simulation (top), followed by three different reconstructions of the snapshot from the leading 10, 40, and 100 eigenimages. [Adapted from Medeiros et al. 2018]

    How is this useful? If images from simulations of a black hole can be represented by sums of eigenimages, so can the actual observations produced by the EHT. By comparing the two sets of observations — real and simulated — to each other within this eigenimage framework, we’ll be able to better understand the components of what we’re observing. In addition, the mathematics of principal component analysis allow for this to work even with sparse interferometric data, as is expected with EHT observations.

    Furthermore, recognizing images that aren’t represented well by the leading eigenimages is equally important. These outlier images can be indicative of flaring or otherwise variable phenomena around the black hole, and identifying moments in which this occurs will help us to better understand the physics of accretion flows around black holes.

    So keep an eye out for the first images from the EHT, expected soon — there’s a good chance that principal component analysis will be helping us to make sense of them!

    Citation

    “Principal Component Analysis as a Tool for Characterizing Black Hole Images and Variability,” Lia Medeiros et al 2018 ApJ 864 7. http://iopscience.iop.org/article/10.3847/1538-4357/aad37a/meta

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 11:19 am on May 28, 2018 Permalink | Reply
    Tags: , , , , EHT - Event Horizon Telescope, , ,   

    From Ethan Siegel: “This Is Why The Event Horizon Telescope Still Doesn’t Have An Image Of A Black Hole” 

    From Ethan Siegel
    May 28, 2018

    1
    The black hole at the center of our Milky Way, simulated here, is the largest one seen from Earth’s perspective. The Event Horizon Telescope should, this year, come out with their first image of what this central black hole’s event horizon looks like. The white circle represents the Schwarzschild radius of the black hole. Ute Kraus, Physics education group Kraus, Universität Hildesheim; background: Axel Mellinger

    Across multiple continents, including Antarctica, an array of radio telescopes observe the galactic center.

    EHT APEX, IRAM, G. Narayanan, J. McMahon, JCMT/JAC, S. Hostler, D. Harvey, ESO/C. Malin


    A view of the different telescopes contributing to the Event Horizon Telescope’s imaging capabilities from one of Earth’s hemispheres. The data taken from 2011 to 2017 should enable us to now construct an image of Sagittarius A*.

    This network, the Event Horizon Telescope (EHT), is imaging, for the first time, a black hole’s event horizon.

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


    SgrA* NASA/Chandra


    Sgr A* from ESO VLT

    2
    The most-visualized black hole of all, as illustrated in the movie Interstellar, shows a predicted event horizon fairly accurately for a very specific class of rotating black holes. Interstellar / R. Hurt / Caltech

    Of all the black holes visible from Earth, the largest is at the galactic center: 37 μas [Microarc-second].

    4
    This multiwavelength view of the Milky Way’s galactic center goes from the X-ray through the optical and into the infrared, showcasing Sagittarius A* and the intragalactic medium located some 25,000 light years away. Using radio data, the EHT will resolve the event horizon of the central black hole. X-ray: NASA/CXC/UMass/D. Wang et al.; Optical: NASA/ESA/STScI/D.Wang et al.; IR: NASA/JPL-Caltech/SSC/S.Stolov

    NASA/Chandra X-ray Telescope

    NASA/ESA Hubble Telescope

    With a theoretical resolution of 15 μas, the EHT should resolve it.

    Despite the incredible news that they’ve detected the black hole’s structure at the galactic center, however, there’s still no direct image.

    5
    A plot of the coverage in space of the area around the galactic center’s black hole from the telescopes whose data has been brought together so far. Additional telescopes will further constrain the black hole’s size, shape and orientation. R.-S. Lu et al, ApJ 859, 1

    They found evidence for an asymmetric source, about 3 Schwarzschild radii large: consistent with Einstein’s prediction of 2.5.

    66
    Two of the possible models that can successfully fit the Event Horizon Telescope data thus far. Both show an off-center, asymmetric event horizon that’s enlarged versus the Schwarzschild radius, consistent with the predictions of Einstein’s General Relativity. R.-S. Lu et al, ApJ 859, 1

    But before the South Pole data, delivered five months ago, can be added, all error sources must be identified.

    South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the National Institute for Standards and Technology. It is funded by the National Science Foundation.


    The South Pole Telescope, a 10 meter radio telescope located at the South Pole, will be the most important addition to the EHT as far as resolving the central black hole goes.

    Earth’s atmospheric turbulence, instrumentation noise, and spurious signals require identification, obtainable through additional imaging.

    8
    A map of the 7 million second exposure of the Chandra Deep Field-South. This region shows hundreds of supermassive black holes, each one in a galaxy far beyond our own. There should be hundreds of thousands of times as many stellar-mass black holes; we’re just waiting for the capability of detecting them. NASA/CXC/B. Luo et al., 2017, ApJS, 228, 2

    Although the data has been combined, novel algorithms must be developed to process them into an image.

    9
    Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole’s accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results. GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799

    Only two black holes, Sagittarius A* and Messier 87, could have event horizon “silhouettes” imaged.

    10
    The second-largest black hole as seen from Earth, the one at the center of the galaxy Messier 87, is shown in three views here. Despite its mass of 6.6 billion Suns, it is over 2000 times farther away than Sagittarius A*. It may not be resolvable by the EHT.Top, optical, Hubble Space Telescope / NASA / Wikisky; lower left, radio, NRAO / Very Large Array (VLA); lower right, X-ray, NASA / Chandra X-ray telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    New data will be taken annually, improving the future, overall pictures through subsequent analysis.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    NSF CfA Greenland telescope

    Greenland Telescope

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    Over the coming months, preliminary images will show the:

    size,
    shape,
    changes,
    and surrounding environment,

    of our first directly-observed black holes.

    11
    High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA, V. Fish et al., arXiv:1309.3519

    Some of the possible profile signals of the black hole’s event horizon as simulations of the Event Horizon Telescope indicate.

    See the full article here .


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

    Please help promote STEM in your local schools.
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    Stem Education Coalition

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

     
  • richardmitnick 3:36 pm on May 1, 2018 Permalink | Reply
    Tags: , , , , , EHT - Event Horizon Telescope, , Greenland Telescpe achieves "first light" and more, ,   

    From Harvard Smithsonian Center for Astrophysics: “Greenland Telescope Opens New Era of Arctic Astronomy” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    May 1, 2018

    Megan Watzke
    Harvard-Smithsonian Center for Astrophysics
    +1 617-496-7998
    mwatzke@cfa.harvard.edu

    Peter Edmonds
    Harvard-Smithsonian Center for Astrophysics
    +1 617-571-7279
    pedmonds@cfa.harvard.edu

    NSF CfA Greenland telescope

    NSF CfA Greenland telescope

    To study the most extreme objects in the Universe, astronomers sometimes have to go to some extreme places themselves. Over the past several months, a team of scientists has braved cold temperatures to put the finishing touches on a new telescope in Greenland. [This is a major gain for astronomy in the Northern Hemisphere, which sometimes seems to be less productive than the astronomical assets in the Southern Hemsphere.]

    Taking advantage of excellent atmospheric conditions, the Greenland Telescope is designed to detect radio waves from stars, galaxies and black holes. One of its primary goals is to join the Event Horizon Telescope (EHT), a global array of radio dishes that are linked together to make the first image of a supermassive black hole.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    The Greenland Telescope has recently achieved two important milestones, its “first light” and the successful synchronization with data from another radio telescope. With this, the Greenland Telescope is ready to help scientists explore some of the Universe’s deepest mysteries.

    “We can officially announce that we are open for business to explore the cosmos from Greenland,” said Timothy Norton of the Harvard-Smithsonian Center for Astrophysics (CfA) and Senior Project Manager for the telescope. “It’s an exciting day for everyone who has worked so hard to make this happen.”

    In December 2017, astronomers were able to successfully detect radio emission from the Moon using the Greenland Telescope, an event astronomers refer to as “first light.” Then in early 2018, scientists combined data from the Greenland Telescope’s observations of a quasar with data from the Atacama Large Millimeter/submillimeter Array, or ALMA.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    The data from the Greenland Telescope and ALMA were synchronized so that they acted like two points on a radio dish equal in size to the separation of the two observing sites, an achievement that is called “finding fringes.”

    “This represents a major step in integrating the telescope into a larger, global network of radio telescopes,” said Nimesh Patel of CfA. “Finding fringes tells us that the Greenland Telescope is working as we hoped and planned.”

    The Greenland Telescope is a 12-meter radio antenna that was originally built as a prototype for ALMA. Once ALMA was operational in Chile, the telescope was repurposed to Greenland to take advantage of the near-ideal conditions of the Arctic to study the Universe at specific radio frequencies.

    The Greenland location also allows interferometry with the Submillimeter Array in Hawaii, ALMA and other radio dishes, to become a part of the northernmost component of the EHT. This extends the baseline of this array in the north-south direction to about 12,000 km (about 7,500 miles).

    CfA Submillimeter Array Mauna Kea, Hawaii, USA, Altitude 4,080 m (13,390 ft)

    “The EHT essentially turns the entire globe into one giant radio telescope, and the farther apart radio dishes in the array are, the sharper the images the EHT can make,” said Sheperd Doeleman of the CfA and leader of the EHT project. “The Greenland Telescope will help us obtain the best possible image of a supermassive black hole outside our galaxy.”

    The Greenland Telescope joined the EHT observing campaign in the middle of April 2018 to observe the supermassive black hole at the center of the galaxy M87. This supermassive black hole and the one in our galaxy are the two primary targets for the EHT, because the apparent sizes of their event horizons are larger than for any other black hole. Nevertheless exquisite telescope resolution is required, equivalent to reading a newspaper on the Moon. This capability is about a thousand times better than what the best optical telescopes in the world can achieve.

    Scientists plan to use these observations to help test Einstein’s theory of General Relativity in environments where extreme gravity exists, and probe the physics around black holes with unprecedented detail.

    In 2011, NSF, the Associated Universities, Inc. (AUI)/National Radio Astronomy Observatory (NRAO) awarded the antenna to the Smithsonian Astrophysical Observatory (SAO) for relocation to Greenland. SAO’s project partner, the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA) of Taiwan, led the effort to refurbish and rebuild the antenna to prepare it for the cold climate of Greenland’s ice sheet. In 2016, the telescope was shipped to the Thule Air Base, Greenland, 750 miles inside the Arctic Circle, where it was reassembled at this sea-level coastal site. A future site is under consideration a the summit of the Greenland ice sheet where we will be able to take advantage of lower water vapor in the atmosphere overhead and achieve even better resolution at the higher operating frequencies.

    More information on the Greenland Telescope can be found at https://www.cfa.harvard.edu/greenland12m/

    Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    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 6:19 pm on March 6, 2018 Permalink | Reply
    Tags: A Decade of Atmospheric Data Aids Black Hole Observers, , , , , EHT - Event Horizon Telescope, , ,   

    From Eos: “A Decade of Atmospheric Data Aids Black Hole Observers” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    2 February 2018
    Kimberly M. S. Cartier

    1
    The Atacama Pathfinder Experiment (APEX) 12-meter telescope in Chile’s Atacama Desert, shown here, will join others to image the immediate surroundings of a black hole this April during an optimum observing period calculated by scientists using global weather data. Credit: European Southern Observatory/H. H. Heyer, CC BY 4.0

    A worldwide collaboration of radio astronomers called the Event Horizon Telescope (EHT) is taking a close look at the atmosphere here on Earth to get a better view of an elusive area of deep space.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    Thanks to their recent modeling of the past 10 years of global atmospheric and weather data, they can now predict when their nine radio telescopes and arrays scattered around the world are most likely to have the clear view they need to make their extraordinary simultaneous observations.

    The scientists’ quarry is the perilous boundary of a black hole, called the event horizon, and the surrounding region of space. Their target is not just any black hole: It’s the hulking, supermassive black hole that lurks at the heart of the Milky Way.

    “You have to get all the participating observatories to collectively agree to give the EHT folks time on the sky when they ask for it…and that’s a big deal,” said Scott Paine, an astrophysicist at the Smithsonian Astrophysical Observatory (SAO) in Cambridge, Mass., who also happens to be an atmospheric scientist. “When an observatory commits several days to EHT to observe, we want the EHT to make good use of it, because it represents a significant investment for the observatory.”

    Trying to ensure that EHT scientists would make the most of valuable worldwide observing time, Paine advised that they approach the problem scientifically using global atmospheric records. Along with EHT director and SAO astrophysicist Sheperd Doeleman, he spearheaded the creation of a model that predicts the probability of good simultaneous observations at all sites using data gathered by the National Oceanic and Atmospheric Administration (NOAA). Using this new model, the EHT collaboration is coordinating a weeklong observing campaign that will take place this coming April.

    It’s not the first time the collaboration will peer at our galaxy’s central black hole, which is known as Sgr A* and weighs in at about 4 million times the mass of our Sun.

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

    SgrA* NASA/Chandra

    The inaugural attempt took place in April 2017, and the observers are still crunching the data from that first try.

    Even though the collaborators haven’t yet seen the images from that initial look, they geared up to try again, with the expectation of better results. This April and into the future, they hope to achieve the best “seeing” possible for the collection of EHT telescopes and arrays, thanks to their newly developed tools for selecting dates and times of optimal meteorological conditions for the overall observing network.

    “We’re trying to make coherent a network the size of the globe, which is incredible when you think about it,” Doeleman told National Geographic. “It’s a heartbreaker if you [plan for] a night and bad weather closes in” or, conversely, if observations are canceled for a night that the weather is clear, he added.

    “These tools allow us to determine the ideal observing windows for EHT observations and to assess the suitability and impact of new EHT sites,” said Harvard University undergraduate student Rodrigo Córdova Rosado in a recent presentation of this work. Córdova Rosado, a junior who worked on the project with Paine and Doeleman, presented a poster about this research on 9 January at the 231st meeting of the American Astronomical Society in National Harbor, Md.

    A Worldwide Telescope Array

    Although a black hole, by definition, does not emit light, gas and dust surrounding the black hole emit copious light as the incredible gravity of the black hole pulls the material onto itself. The brilliant glow, in turn, silhouettes the black hole, an extraordinarily compressed dot of mass, also known as a singularity.

    Because of the black hole’s ultracompact size, imaging its immediate environment requires an observing technique called very long baseline interferometry (VLBI). VLBI coordinates observations from multiple radio telescopes around the globe to amplify the light from a target and increase the signal-to-noise ratio of an observation. The wider the physical footprint of the array used in VLBI is, the stronger and clearer the radio signal is. Astronomers have used VLBI to view stars coalescing from giant gas clouds, and they plan to use it to glimpse protoplanets forming in circumstellar disks.

    EHT’s nine radio telescopes and arrays at seven observing sites compose the largest VLBI array in the world. Getting onto the observing schedule at any one of the telescopes is very competitive, and negotiating for simultaneous observing time on all nine is even more difficult.

    A Two-Pronged Predictive Approach

    Deciding when to observe requires solving two problems at once, according to Paine. “There’s the strategic problem,” he said, “that is, which week or two weeks are you going to ask for from the observatories.”

    The second is a tactical problem. “Once you’ve got your block of time, and you’re allowed to use a certain number of days within an allocated period, which ones are you going to trigger observations on?” He added, “We’ve been looking at both problems.”

    That’s where NOAA comes in. Córdova Rosado tackled the first problem by gathering global weather data from NOAA’s Global Forecast System (GFS) recorded from 2007 to 2017 at approximately 6-hour intervals. Because EHT observes using radio waves, the researchers were primarily interested in records of relative humidity, ozone mixing ratio, cloud water vapor ratios, and temperature at each of the sites because each of those atmospheric conditions affects the quality of observations. Córdova Rosado ran those data through an atmospheric model that Paine had created to calculate how opaque the atmosphere appears at EHT’s observing frequency of 221 GHz, or a wavelength of 1.4 millimeters.

    3
    A map of worldwide relative humidity data on 2 February 2012 from NOAA’s Global Forecast System. The color gradient shows areas of low (blue) and high (red) relative humidity between 0 and 30 millibars above ground-level pressure—essentially the relative humidity at the surface for GFS data. Researchers with the Event Horizon Telescope collaboration extracted data from maps such as this, generated for many atmospheric layers, to determine the humidity along an observing direction. Credit: Córdova Rosado et al., 2018; data from NOAA/National Centers for Environmental Information

    According to Vincent Fish, a research scientist at the Massachusetts Institute of Technology (MIT) Haystack Observatory in Westford, Mass., coordinated, ground-based radio observations of the galactic center thrive at 221 GHz. “At longer observing wavelengths,” he explained in an MIT press release, “the source would be blurred by free electrons…and we wouldn’t have enough resolution to see the predicted black hole shadow. At shorter wavelengths, the Earth’s atmosphere absorbs most of the signal.” Fish was not involved in this research.

    EHT Sites Prefer It Dry

    Córdova Rosado statistically combined each of the yearly opacity trends to calculate for each day of the year the probability that Sgr A* would have favorable observing conditions simultaneously at all seven sites. The team found that the second and third weeks of April were the best times of year for EHT to observe Sgr A*. The middle of February was a good backup observing window for both the Milky Way’s center and another black hole target. The Northern Hemisphere late spring and summer ranked lowest among possible observing months because of seasonal weather variability.

    4
    The median opacity towards Sgr A* for a typical year at five EHT observing sites (solid lines) and variability ranges (shaded regions), calculated at weekly intervals by the atmospheric model developed by Paine and Córdova Rosado. Opacity values near 1 indicate poor observing conditions, and values near zero indicate good “seeing.” Sites shown here are the Atacama Large Millimeter/Submillimeter Array ( ALMA; red), the Large Millimeter Telescope (LMT; black), the Submillimeter Array (SMA; green), the Submillimeter Telescope (SMT; blue), and the South Pole Telescope (SPT; orange). Credit: Rodrigo Córdova Rosado.

    Some sites, like the South Pole Telescope and the Atacama Large Millimeter/ Submillimeter Array (ALMA) in Chile, offer remarkably stable opacities throughout the year because the areas enjoy consistently low humidity. For more variable Northern Hemisphere sites, the winter months provide the most favorable observing conditions.

    Fish commented that “the probability of having really good weather at every site is almost zero.” However, according to Paine, each of the EHT sites may serve a different purpose for each target, either to act as a mission-critical observing location or to enhance the image quality. Which role an observatory plays during a particular observing run depends on the target location and date, he explained. The team may not need perfect conditions at all sites for every observation.

    More Telescopes, More Targets

    Although climate change has undoubtedly affected the 2007–2017 NOAA meteorological data, it hasn’t significantly influenced the EHT calculations, said Paine. Humidity outweighs temperature as the most important factor for getting clear radio observations, he explained. Although the global average humidity rose slightly over the 10 years of GFS data, he noted, it didn’t go up by enough to alter the team’s predictions.

    Paine described the EHT atmospheric model as the first step in creating what he called a “merit function” that he and his colleagues will use to assess the value of conducting observations on a particular day. Continued access to NOAA’s GFS data, he said, will be critical to making the best use of limited observing time.

    “[NOAA’s] resources are not only used for weather and climate tasks, but they’re also getting leveraged for things like astronomy,” he said. “We’re fortunate to have this resource for optimizing very expensive astronomical observations.”

    —Kimberly M. S. Cartier (@AstroKimCartier), News Writing and Production Intern

    Correction, 6 February 2018: An image caption and a researcher’s statement have been updated to more accurately describe the associated data.

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 12:59 pm on February 23, 2018 Permalink | Reply
    Tags: , , , , EHT - Event Horizon Telescope, ,   

    From University of Arizona: “UA Leads Project on Big Data and Black Holes” 

    U Arizona bloc

    University of Arizona

    Feb. 21, 2018
    Daniel Stolte

    Chi-Kwan Chan waves his hand a few inches above a matchbox-size device. On a dark computer monitor, a million light dots appear as a solid sheet, each dot representing a light particle.

    1
    The Event Horizon Telescope is a virtual Earth-size telescope, achieving its globe-spanning baseline by combining precisely synchronized observations made at various sites around the world. (Image: Dan Marrone)

    The photon sheet hovers above a black disc simulating a black hole. With a slow turn of the hand, the sheet approaches the black hole. As it passes, the gravitational monster swallows any light particles in its direct path, creating a circular cutout in the sheet of particles. The rest of the particles are on track to move past the black hole, or so it seems. But they don’t get very far: Instead of continuing along their straight lines of travel, their paths bend inward and they loop around the black hole and converge in one point, forming a sphere of photons around it.

    “What you see here is light trapped in the fabric of space and time, curving around the black hole by its massive gravity,” explains Chan, an assistant astronomer at the University of Arizona’s Steward Observatory, who developed the computer simulation as part of his research into how black holes interact with things that happen to be nearby.

    U Arizona Steward Observatory at Kitt Peak, AZ, USA, altitude 2,096 m (6,877 ft)

    The demonstration was part of an event at UA’s Flandrau Science Center & Planetarium on Feb. 16 to kick off a UA-led, international project to develop new technologies that enable scientists to transfer, use and interpret massive datasets.

    Known as Partnerships for International Research and Education program, or PIRE, the effort is funded with $6 million over five years by the National Science Foundation, with an additional $3 million provided by partnering institutions around the world. While the award’s primary goal is to spawn technology that will help scientists take the first-ever picture of the supermassive black hole at the center of our Milky Way, the project’s scope is much bigger.

    What looks like a fun little animation on Chan’s computer screen is in fact a remarkable feat of computing and programming: As the computational astrophysicist drags virtual photons around a virtual black hole, a powerful graphics processor solves complex equations that dictate how each individual light particle would behave under the influence of the nearby black hole — simultaneously and in real time.

    Study Relies on Simulations

    Unlike the crew in the movie “Interstellar,” astrophysicists can’t travel to a black hole and study it from close range. Instead, they have to rely on simulations that mimic black holes based on their physical properties that are known to — or thought to — govern these most extreme objects in the universe.

    Chan belongs to a group of researchers in an international collaboration called the Event Horizon Telescope, or EHT, that is gearing up to capture the first picture of a black hole — not just any black hole, but the supermassive black hole in the center of our galaxy. Called Sagittarius A* (referred to as “Sgr A Star,” pronounced Sag A Star), this object has the mass of more than 4 million suns.

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

    Since nothing, not even light, can escape a black hole, it casts a silhouette in the background of in-falling plasma that is too small to be resolved by any single telescope. So far, the existence of Sgr A* has been inferred from indirect observations only, such as the intriguing choreography of stars in its vicinity, whose orbits clearly outline an unseen, incomprehensibly large mass.

    “Imaging the black hole at the center of our galaxy from Earth is like trying to read the date on a dime on the East Coast from the UA campus,” says Feryal Özel, a professor of astronomy and physics at Steward and a co-investigator on the project. “There is not one telescope in existence that could do that.”

    The EHT is an array of radio telescopes on five continents that together act as a virtual telescope the size of the Earth — the aperture needed to image “the date on the dime,” or in this case the supermassive black hole Sag A*.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    Greenland Telescope

    To accomplish this, the individual telescopes must be precisely synced in time. Because existing internet cables and even satellite communication are too coarse to ensure this, the researchers rely on atomic clocks and … FedEx (more on that later).

    “Our PIRE project is a prime example of the kind of innovation you can only get by leveraging the innovative, intellectual capital in academia,” says Dimitrios Psaltis, the principal investigator on the project. “By its very nature, this project is multidisciplinary and requires expertise in areas ranging from detector development to high-performance computing and theoretical physics.”

    At peak activity, the EHT will collect more data than any project before, according to Psaltis, a professor of astronomy and physics at the UA.

    “We’re talking petabytes every single night,” he says, and this is comparable to the three petabytes of video uploaded each day on YouTube. “Post-processing is a huge effort, and we will need additional data to improve the science that we hope will come from these observations.”

    The team uses graphic processing units, or GPUs — processors developed for gaming that are capable of performing many calculations in parallel. This makes them more efficient and energy-saving than “regular” computer processing units, or CPUs.

    “We hope that this technology will transfer to other areas of science and life,” said Joaquin Ruiz, dean of the UA College of Science, at the launch event.

    Applications Could Be Extensive

    The PIRE project is expected to spin off technologies that go beyond the project’s primary goal. The fast processing of large data in real time and the efficient use of resources distributed across the globe will have applications ranging from self-driving cars to renewable energy production and national defense. Examples also include augmented reality applications that are good at fast computing with real-time input and minimum computing resources, Özel explains.

    “This could be used, for example, in visual aids for security efforts around the globe where data connection bandwidth and energy supplies are limited,” she says, “so you want devices that make maximum use of precious resources available in those scenarios.”

    The PIRE project team integrates researchers in the U.S., Germany, Mexico and Taiwan. Education of students and early career scientists is a key component, providing internally collaborative, hands-on experience in instrument technology, high-performance computing, and big and distributed data science. There also are monthly webinars and hackathons, as well as summer schools, that will be sponsored every year.

    Fast and reliable real-time communication channels are crucial in syncing up telescopes scattered around the globe for observations, and improving such technology is one of PIRE’s goals. For now, EHT scientists rely on video chat, phones and whiteboards to keep track of each telescope location’s status. During a rare stretch of a few days in April 2017, skies were mostly clear in all nine observing sites that are part of the EHT array — including Arizona, Hawaii, Chile, Mexico and Antarctica.

    The South Pole Telescope, or SPT, site was incorporated under another NSF grant to the UA, with Dan Marrone as principal investigator. Last year was the first year that the full EHT observed as an array, and the first year in which the SPT participated.

    During that first observation run, the observing stations that together make up the EHT pointed at the Milky Way’s center and collected radio waves originating from the supermassive black hole over the course of several nights. By obtaining the first-ever images of black holes, researchers will be able to directly test Einstein’s theory of general relativity in extreme conditions.

    “Each telescope records its observation data onto a bunch of physical hard drives,” explains Marrone, an associate professor at Steward and a co-investigator on the PIRE award. “Precisely time-stamped, the drives are loaded into crates and delivered to processing centers in Cambridge, Massachusetts, and Bonn, Germany, via FedEx.”

    The EHT data are shipped on physical carriers because current internet data pipelines aren’t up to the scope this endeavor requires. Then data experts combine the literal truckloads of data, synchronize it according to their time stamps and process it to extract the signal from the black hole, which in the raw data is buried under a blanket of noise and error — the inevitable side effects of turning the Earth into one giant telescope.

    “PIRE is an international project that not only will revolutionize worldwide efforts to study black holes, but usher astronomical projects into the era of big and distributed data science,” Psaltis says. “By awarding the PIRE project, the NSF has tasked the UA and its collaborators to contribute solutions that may inform many areas of technology, including the internet of tomorrow.”

    See the full article here .

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    U Arizona campus

    The University of Arizona (UA) is a place without limits-where teaching, research, service and innovation merge to improve lives in Arizona and beyond. We aren’t afraid to ask big questions, and find even better answers.

    In 1885, establishing Arizona’s first university in the middle of the Sonoran Desert was a bold move. But our founders were fearless, and we have never lost that spirit. To this day, we’re revolutionizing the fields of space sciences, optics, biosciences, medicine, arts and humanities, business, technology transfer and many others. Since it was founded, the UA has grown to cover more than 380 acres in central Tucson, a rich breeding ground for discovery.

    Where else in the world can you find an astronomical observatory mirror lab under a football stadium? An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

     
  • richardmitnick 5:44 pm on February 17, 2018 Permalink | Reply
    Tags: , , , , EHT - Event Horizon Telescope, , , ,   

    From ESO: “7. Challenges in Obtaining an Image of a Supermassive Black Hole” 

    ESO 50 Large

    European Southern Observatory

    “Seeing a black hole” has been a long-cherished desire for many astronomers, but now, thanks to the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) projects, it may no longer be just a dream.

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    Global mm-VLBI Array

    Greenland Telescope

    To make it possible to image the shadow of the event horizon of Sagittarius A* [SgrA*], many researchers and cutting-edge technologies have been mobilised — because obtaining an image of a black hole is not as easy as snapping a photo with an ordinary camera.

    Sagittarius A* has a mass of approximately four million times that of the Sun, but it only looks like a tiny dot from Earth, 26 000 light-years away.

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

    NASA/Chandra Telescope

    To capture its image, incredibly high resolution is needed. As explained in the fifth post of this blog series, the key is to use Very-Long-Baseline Interferometry (VLBI), a technique that combines the observing power of and the data from telescopes around the world to create a virtual giant radio telescope.

    The resolution of a telescope can be calculated from the radio wavelength the telescope is observing at and the size of the telescope — or in VLBI, the distance between the antennas. However, while actually observing, several kinds of noise and errors interfere with the telescope’s performance and affect the resolution.

    In VLBI, each antenna is equipped with an extremely precise atomic clock to record the time at which radio signals from the target object were received. The gathered data are synthesised using the times as a reference, so that the arrival time of the radio waves to each antenna can be accurately adjusted.

    But this process isn’t always straightforward because the Earth’s atmosphere blocks a certain range of wavelengths. Several kinds of molecules such as water vapour absorb a fraction of radio waves that pass through the atmosphere, with shorter wavelengths more susceptible to absorption. To minimise the effect of atmospheric absorption, radio telescopes are built at high and dry sites, but even then they are still not completely immune from the effect.

    The tricky part of this absorption effect is that the direction of a radio wave is slightly changed when it passes through the atmosphere containing water vapour. This means that the radio waves arrive at different times at each antenna, making it difficult to synthesise the data later using the time signal as a reference. And even worse: since VLBI utilises antennas located thousands of kilometres apart, it has to take into account the differences in the amount of water vapour in the sky above each site, as well as the large fluctuations of water vapour content during the observation period. In optical observations, these fluctuations make the light of a star flicker and lower the resolution. Radio observations have similar problems.

    “We have only a few ways to reduce this effect in VLBI observations,” explains Satoki Matsushita at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) of Taiwan. “If there is a compact object emitting intense radiation near the target object, we can remove most of the effect of refraction of radio waves by water vapour by using such an intense radiation source as a reference. However, no such intense reference source has been found near Sagittarius A* so far. And even if there is a reference source, there are still necessary conditions that must be satisfied: the telescopes need to have the ability to observe the target object and reference object at the same time; or the telescopes need to have the high-speed drive mechanism to quickly switch the observation between the target object and the reference object. Unfortunately, not all telescopes participating in the EHT/GMVA observations have this capability. One of the methods to remove the effect is to equip each antenna with an instrument to measure the amount of water vapour, but ALMA is the only telescope that has adopted this method at this point.”

    Another major challenge in imaging a black hole is obtaining a high-quality image. By combining the data collected by antennas thousands of kilometres apart, VLBI achieves a resolution equivalent to a radio telescope several thousands of kilometres in diameter. However, VLBI also has a lot of large blank areas that are not covered by any of the antennas. These missing parts make it difficult for VLBI to reproduce a high-fidelity image of a target object from the synthesised data. This is a common problem for all radio interferometers, including ALMA, but it can be more serious in VLBI where the antennas are located very far apart.

    It might be natural to think that a higher resolution means a higher image quality, as is the case with an ordinary digital camera, but in radio observations the resolution and image quality are quite different things. The resolution of a telescope determines how close two objects can be to each other and yet still be resolved as separate objects, while the image quality defines the fidelity in reproducing the image of the structure of the observed object. For example, imagine a leaf, which has a variety of veins. The resolution is the ability to see thinner vein patterns, while the image quality is the ability to capture the overall spread of the leaf. In normal human experience, it would seem bizarre if you could see the very thin veins of a leaf but couldn’t grasp a complete view of the leaf — but such things happen in VLBI, since some portions of data are inevitably missing.

    1
    This infographic illustrates how ALMA contributes to the EHT observations. With its shorter baseline, ALMA is sensitive to larger scales than the EHT and so ALMA can fill in the lower-resolution, larger-scale structures that the EHT misses. Credit: NRAO

    Researchers have been studying data processing methods to improve image quality for almost as long as the history of the radio interferometer itself, so there are some established methods that are already widely used, while others are still in an experimental phase. In the Event Horizon Telescope (EHT) and the Global mm-VLBI Array (GMVA) projects, which are both aiming to capture the shadow of a black hole’s event horizon for the first time, researchers began to develop effective image analysis methods using simulation data well before the start of the observations.

    2
    A simulated image of the supermassive black hole at the centre of the M87 galaxy. The dark gap at the centre is the shadow of the black hole. Credit: Monika Moscibrodzka (Radboud University)

    The observations with the EHT and the GMVA were completed in April 2017. The data collected by the antennas around the world has been sent to the US and Germany, where data processing will be conducted with dedicated data-processing computers called correlators. The data from the South Pole Telescope, one of the participating telescopes in the EHT, will arrive at the end of 2017, and then data calibration and data synthesis will begin in order to produce an image, if possible. This process might take several months to achieve the goal of obtaining the first image of a black hole, which is eagerly awaited by black hole researchers and the general astronomical community worldwide.

    This lengthy time span between observations and results is normal in astronomy, as the reduction and analysis of the data is a careful, time-consuming process. Right now, all we can do is wait patiently for success to come — for a long-held dream of astronomers to be transformed into a reality.

    Until then, this is the last post in our blog series about the EHT and GMVA projects. When the results become available in early 2018, we’ll be back with what will hopefully be exciting new information about our turbulent and fascinating galactic centre

    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.

    Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

    ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

    SPECULOOS four 1m-diameter robotic telescopes 2016 in the ESO Paranal Observatory, 2,635 metres (8,645 ft) above sea level

    ESO TAROT telescope at Paranal, 2,635 metres (8,645 ft) above sea level

    ESO ExTrA telescopes at Cerro LaSilla at an altitude of 2400 metres

     
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