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  • richardmitnick 7:22 am on May 27, 2017 Permalink | Reply
    Tags: , , Fifth force, , Sag A*, , UCLA Galactic Center Group   

    From KECK: “New Method of Searching for Fifth Force” 

    Keck Observatory

    Keck Observatory.
    Keck, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland

    Keck Observatory

    1
    The orbits of two stars, S0-2 and S0-38 located near the Milky Way’s supermassive black hole will be used to test Einstein’s theory of General Relativity and potentially generate new gravitational models. IMAGE CREDIT: S. SAKAI/A.GHEZ/W. M. KECK OBSERVATORY/ UCLA GALACTIC CENTER GROUP

    W. M. Keck Observatory Data Leads To First Of Its Kind Test of Einstein’s Theory of General Relativity.

    May 26, 2017
    No writer credit found.

    A UCLA-led team has discovered a new way of probing the hypothetical fifth force of nature using two decades of observations at W. M. Keck Observatory, the world’s most scientifically productive ground-based telescope.

    There are four known forces in the universe: electromagnetic force, strong nuclear force, weak nuclear force, and gravitational force. Physicists know how to make the first three work together, but gravity is the odd one out. For decades, there have been theories that a fifth force ties gravity to the others, but no one has been able to prove it thus far.

    “This is really exciting. It’s taken us 20 years to get here, but now our work on studying stars at the center of our galaxy is opening up a new method of looking at how gravity works,” said Andrea Ghez, Director of the UCLA Galactic Center Group and co-author of the study.

    The research is published in the current issue of Physical Review Letters.

    Ghez and her co-workers analyzed extremely sharp images of the center of our galaxy taken with Keck Observatory’s adaptive optics (AO). Ghez used this cutting-edge system to track the orbits of stars near the supermassive black hole located at the center of the Milky Way.

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

    Their stellar path, driven by gravity created from the supermassive black hole, could give clues to the fifth force.

    “By watching the stars move over 20 years using very precise measurements taken from Keck Observatory data, you can see and put constraints on how gravity works. If gravitation is driven by something other than Einstein’s theory of General Relativity, you’ll see small variations in the orbital paths of the stars,” said Ghez.

    2
    Pictured above: UCLA Professor of Astrophysics and Galactic Center Group Director Andrea Ghez, a Keck Observatory astronomer and recipient of the 2015 Bakerian Medal. IMAGE CREDIT: KYLE ALEXANDER

    This is the first time the fifth force theory has been tested in a strong gravitational field such as the one created by the supermassive black hole at the center of the Milky Way. Historically, measurements of our solar system’s gravity created by our sun have been used to try and detect the fifth force, but that has proven difficult because its gravitational field is relatively weak.

    “It’s exciting that we can do this because we can ask a very fundamental question – how does gravity work?” said Ghez. “Einstein’s theory describes it beautifully well, but there’s lots of evidence showing the theory has holes. The mere existence of supermassive black holes tells us that our current theories of how the universe works are inadequate to explain what a black hole is.”

    Ghez and her team, including lead author Aurelien Hees and co-author Tuan Do, both of UCLA, are looking forward to summer of 2018. That is when the star S0-2 will be at its closest distance to our galaxy’s supermassive black hole. This will allow the team to witness the star being pulled at maximum gravitational strength – a point where any deviations to Einstein’s theory is expected to be the greatest.

    About Adaptive Optics

    W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere.

    Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and our current systems now deliver images three to four times sharper than the Hubble Space Telescope. AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors.

    See the full article here .

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    Mission
    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.
    Keck UCal

     
  • richardmitnick 1:59 pm on April 29, 2017 Permalink | Reply
    Tags: Ask Ethan: What should a black hole’s event horizon look like?, , , , , , Sag A*   

    From Ethan Siegel: “Ask Ethan: What should a black hole’s event horizon look like?” 

    Ethan Siegel
    Apr 29, 2017

    1
    An illustration of a black hole. Despite how dark it is, all black holes are thought to have formed from normal matter alone, but illustrations like these are only partially accurate. Image credit: NASA / JPL-Caltech.

    You might think that it should be all black, but then how would we see it?

    “It is conceptually interesting, if not astrophysically very important, to calculate the precise apparent shape of the black hole… Unfortunately, there seems to be no hope of observing this effect.” -Jim Bardeen

    Earlier this month, telescopes from all around the world took data, simultaneously, of the Milky Way’s central black hole.

    Here is the Event Horizon Telescope Array

    Event Horizon Telescope map

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

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Also involved:

    European VLBI

    Of all the black holes that are known in the Universe, the one at our galactic center — Sagittarius A* — is special.

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

    From our point of view, its event horizon is the largest of all black holes. It’s so large that telescopes positioned at different locations on Earth should be able to directly image it, if they all viewed it simultaneously. While it will take months to combine and analyze the data from all the different telescopes, we should get our first image of an event horizon by the end of 2017. So what will it looks like? That’s the question of Dan Barrett, who’s seen some illustrations and is a bit puzzled:

    Shouldn’t the event horizon completely surround the black hole like an egg shell? All the artist renderings of a black hole are like slicing a hard boiled egg in half and showing that image. How is it that the event horizon does not completely surround the black hole?

    There are a few different classes of illustrations floating around, to be sure. But which ones, if any, are correct?

    2
    Artwork illustrating a simple black circle, perhaps with a ring around it, is an oversimplified picture of what an event horizon looks like. Image credit: Victor de Schwanberg.

    The oldest type of illustration is simply a circular, black disk, blocking out all the background light from behind it. This makes sense if you think about what a black hole actually is: a collection of mass that’s so great and so compact that the escape velocity from its surface is greater than the speed of light! Since nothing can move that quickly, not even the forces or interactions between the particles inside the black hole, the inside of a black hole collapses to a singularity, and an event horizon is created around the black hole. From this spherical region of space, no light can escape, and so it should appear as a black circle, from any perspective, superimposed on the background of the Universe.

    3
    A black hole isn’t just a mass superimposed over an isolated background, but will exhibit gravitational effects that stretch, magnify and distort background light due to gravitational lensing. Image credit: Ute Kraus, Physics education group Kraus / Axel Mellinger.

    But there’s more to the story than that. Because of their gravity, black holes will magnify and distort any background light, due to the effect of gravitational lensing. This is a more detailed and accurate illustration of what a black hole looks like, as it also possesses an apparent event horizon sized appropriately with the curvature of space in General Relativity.

    Unfortunately, these illustrations are flawed, too: they fail to account for foreground material and for accretion around the black hole. Some illustrations, though, do successfully add these in.

    4
    An illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets, may describe the black hole at the center of our galaxy in many regards. Image credit: Mark A. Garlick.

    Because of their tremendous gravitational effects, black holes will form accretion disks in the presence of other sources of matter. Asteroids, gas clouds, or even entire stars will be torn apart by the tidal forces coming from an object as massive as a black hole. Due to the conservation of angular momentum, and of collisions between the various infalling particles, a disk-like object will emerge around the black hole, which will heat up and emit radiation. In the innermost regions, particles occasionally fall in, adding to the mass of the black hole, while the material in front of the black hole will obscure part of the sphere/circle you’d otherwise see.

    But the event horizon itself isn’t transparent, and you shouldn’t be able to see the matter behind it.

    4
    The black hole, as illustrated in the movie Interstellar, shows an event horizon fairly accurately for a very specific class of rotating black holes. Image credit: Interstellar / R. Hurt / Caltech.

    It might seem surprising that a Hollywood film — Interstellar — has a more accurate illustration of a black hole than many of the professional pieces of artwork created for/by NASA, but misconceptions abound, even among professionals, when it comes to black holes. Black holes don’t suck matter in; they simply gravitate. Black holes don’t tear things apart because of any extra force; it’s simply tidal forces — where one part of the infalling object is closer to the center than another — that does it. And most importantly, black holes rarely exist in a “naked” state, but rather exist in the vicinity of other matter, such as at the center of our galaxy.

    5
    An X-ray / Infrared composite image of the black hole at the center of our galaxy: Sagittarius A*. It has a mass of about four million Suns, and is found surrounded by hot, X-ray emitting gas. Image credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI.

    So with all of that in mind, what are the hard-boiled-egg images that have been going around? Remember, we can’t image the black hole itself, because it doesn’t emit light! All we can do is look at a particular wavelength, and see a combination of the emitting light that comes from around, behind and in front of the black hole itself. The expected signal, indeed, does resemble a split hard-boiled egg.

    6
    Some of the possible profile signals of the black hole’s event horizon as simulations of the Event Horizon Telescope indicate. Image credit: High-Angular-Resolution and High-Sensitivity Science Enabled by Beamformed ALMA, V. Fish et al., arXiv:1309.3519

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

    This has to do with what it is we’re imaging. We can’t look in X-rays, because there are simply too few X-ray photons overall. We can’t look in visible light, because the galactic center is opaque it it. And we can’t look in the infrared, because the atmosphere blocks infrared light. But what we can do is look in the radio, and we can do it all over the world, simulataneously, to get the optimal resolution possible.

    The black hole at the galactic center has an angular size of about 37 micro-arc-seconds, while the resolution of this telescope array is around 15 micro-arc-seconds, so we should be able to see it! At radio frequencies, the overwhelming majority of that radiation comes from charged matter particles being accelerated around the black hole. We don’t know how the disk will be oriented, whether there will be multiple disks, whether it will be more like a swarm of bees or more like a compact disk. We also don’t know whether it will prefer one “side” of the black hole, as viewed from our perspective, over another.

    6
    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. Image credit: GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799.

    We fully expect the event horizon to be real, to be of a specific size, and to block all the light coming from behind it. But we also expect that there will be some signal in front of it, that the signal will be messy due to the messy environment around the black hole, and that the orientation of the disk with respect to the black hole will play an important role in determining what we see.

    One side is brighter as the disk rotates towards us; one side is fainter as the disk rotates away. The entire “outline” of the event horizon may be visible as well, thanks to the effect of gravitational lensing. Perhaps most importantly, whether the disk is seen “edge-on” or “face-on” with respect to us will drastically alter the signal, as the 1st and 3rd panels below illustrate.

    7
    The orientation of the accretion disk as either face-on (left two panels) or edge-on (right two panels) can vastly alter how the black hole appears to us. Image credit: ‘Toward the event horizon — the supermassive black hole in the Galactic Center’, Class. Quantum Grav., Falcke & Markoff (2013).

    There are other effects we can test for, including:

    whether the black hole has the right size as predicted by general relativity,
    whether the event horizon is circular (as predicted), or oblate or prolate instead,
    whether the radio emissions extend farther than we thought,

    or whether there are any other deviations from the expected behavior. This is a brand new frontier in physics, and we’re poised to actually test it directly. One thing’s for certain: no matter what it is that the Event Horizon Telescope sees, we’re bound to learn something new and wonderful about some of the most extreme objects and conditions in the Universe!

    See the full article here .

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

     
  • richardmitnick 2:52 pm on April 4, 2017 Permalink | Reply
    Tags: , , Sag A*,   

    From MIT: “Seeing black holes and beyond” 

    MIT News

    MIT Widget

    MIT News

    April 4, 2017
    Haystack Observatory

    A powerful new array of radio telescopes is being deployed for the first time this week, as the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile joins a global network of antennas poised to make some of the highest resolution images that astronomers have ever obtained.

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

    The improved level of detail is equivalent to being able to count the stitches on a baseball from 8,000 miles away.

    Scientists at MIT and other institutions are using a method called VLBI (Very Long Baseline Interferometry) to link a group of radio telescopes spread across the globe into what is, in effect, a telescope the size of our planet. Although the technique of VLBI is not new, scientists have just recently begun extending it to millimeter wavelengths to achieve a further boost in resolving power. And now, the addition of ALMA to global VLBI arrays is providing an unprecedented leap in VLBI capabilities.

    European VLBI

    The inclusion of ALMA was recently made possible through the ALMA Phasing Project (APP), an international effort led by the MIT Haystack Observatory in Westford, Massachusetts, and principal investigator Sheperd Doeleman, now at the Harvard–Smithsonian Center for Astrophysics.

    Before this project, the ALMA dishes worked with each other to make observations as a single array; now, the APP has achieved the synchronizing, or “phasing,” of up to 61 ALMA antennas to function as a single, highly sensitive radio antenna — the most antennas ever phased together. To achieve this, the APP team developed custom software and installed several new hardware components at ALMA, including a hydrogen maser (a type of ultraprecise atomic clock), a set of very-high-speed data reformatters, and a fiber optic system for transporting an 8 gigabyte-per-second data stream to four ultrafast data recorders (the Haystack-designed Mark6). The culmination of these efforts is an order-of-magnitude increase in the sensitivity of the world’s millimeter VLBI networks, and a dramatic boost in their ability to create detailed images of sources that previously appeared as mere points of light.

    “A great many people have worked very hard over the past several years to make this dream a reality,” says Geoff Crew, software lead for the APP. “ALMA VLBI is truly going to be transformative for our science.”

    One of the goals of these new technological innovations is to image a black hole. This month, two international organizations are making observations that will allow scientists to construct such an image for the very first time. And the portrait they’re attempting to capture is close to home: Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way.

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

    So much data will be collected during the two observation periods that it’s faster to fly them to Haystack than it would be to transmit them electronically. Petabytes of data will be flown from telescopes around the world to Haystack for correlation and processing before images of the black hole can be created. Correlation, which registers the data from all participating telescopes to account for the different arrival times of the radio waves at each site, is done using a specialized bank of powerful computers. MIT Haystack is one of the few radio science facilities worldwide with the necessary technology and expertise to correlate this amount of data. Additional correlation for these sessions is being done at the Max Planck Institute for Radio Astronomy in Bonn, Germany.

    Two observing sessions are taking place. The GMVA (Global mm-VLBI Array) session will observe a variety of sources at a wavelength of 3 millimeters, including Sgr A* and other active galactic nuclei, and the EHT (Event Horizon Telescope) session will observe Sgr A* as well as the supermassive black hole at the center of a nearby galaxy, M87, at a wavelength of 1.3 millimeters. The EHT team includes researchers from MIT’s Haystack Observatory and MIT Computer Science and Artificial Intelligence Laboratory (CSAIL), working with the Harvard-Smithsonian Center for Astrophysics and many other organizations.

    Global mm-VLBI Array

    _______________________________________________________________________________________________________________________________________

    Event Horizon Telescope Array

    Event Horizon Telescope map

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

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

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

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    __________________________________________________________________________________________________________________________________

    “Several factors make 1.3 mm the ideal observing wavelength for Sgr A*,” according to APP Project Scientist Vincent Fish. “At longer observing wavelengths, the source would be blurred by free electrons between us and the galactic center, 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.”

    The current observations are the first in a series of groundbreaking studies in VLBI and radio interferometry that will enable dramatic new scientific discoveries. Data from the newly phased ALMA array will also allow better imaging of other distant radio sources via improved data sampling, increased angular resolution, and eventually spectral-line VLBI — observations of emissions from specific elements and molecules.

    “Phasing ALMA has opened whole new possibilities for ultra high-resolution science that will go far beyond the study of black holes,” says Lynn Matthews, commissioning scientist for the APP. “For example, we expect to be able to make movies of the gas motions around stars that are still in the process of forming and map the outflows that occur from dying stars, both at a level of detail that has never been possible before.”

    The black hole images from the data gathered this month will take months to prepare; researchers expect to publish the first results in 2018.

    The MIT Haystack Observatory team of scientists includes Geoff Crew, Vincent Fish, Michael Hecht, Lynn Matthews, Colin Lonsdale, and Sheperd Doeleman (now at the Harvard-Smithsonian Center for Astrophysics).

    The organizations of the APP are: MIT Haystack Observatory (lead organization), Harvard–Smithsonian Center for Astrophysics, Joint ALMA Observatory (Chile), National Radio Astronomy Observatory (NRAO), Max Planck Institute for Radio Astronomy (Germany), University of Concepción (Chile), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA; Taiwan), National Astronomical Observatory of Japan (NAOJ), and Onsala Observatory (Sweden).

    See the full article here .

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

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  • richardmitnick 2:11 pm on March 9, 2017 Permalink | Reply
    Tags: , , , Hubble Dates Black Hole’s Last Big Meal, , Sag A*,   

    From Hubble: “Hubble Dates Black Hole’s Last Big Meal” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    Mar 9, 2017

    Felicia Chou
    NASA Headquarters, Washington, D.C.
    felicia.chou@nasa.gov
    202-358-0257

    Donna Weaver / Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4493 / 410-338-4514
    dweaver@stsci.edu / villard@stsci.edu

    Rongmon Bordoloi
    Massachusetts Institute of Technology, Cambridge, Massachusetts
    617-252-1736
    bordoloi@mit.edu

    1
    Illustration Credit: NASA, ESA, and Z. Levy (STScI)

    For the supermassive black hole at the center of our Milky Way galaxy [Sag A*], it’s been a long time between dinners.


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

    NASA’s Hubble Space Telescope has found that the black hole ate its last big meal about 6 million years ago, when it consumed a large clump of infalling gas. After the meal, the engorged black hole burped out a colossal bubble of gas weighing the equivalent of millions of suns, which now billows above and below our galaxy’s center.

    The immense structures, dubbed the Fermi Bubbles, were first discovered in 2010 by NASA’s Fermi Gamma-ray Space Telescope.


    NASA’s Fermi Gamma-ray Space Telescope

    But recent Hubble observations of the northern bubble have helped astronomers determine a more accurate age for the bubbles and how they came to be.

    “For the first time, we have traced the motion of cool gas throughout one of the bubbles, which allowed us to map the velocity of the gas and calculate when the bubbles formed,” said lead researcher Rongmon Bordoloi of the Massachusetts Institute of Technology in Cambridge. “What we find is that a very strong, energetic event happened 6 million to 9 million years ago. It may have been a cloud of gas flowing into the black hole, which fired off jets of matter, forming the twin lobes of hot gas seen in X-ray and gamma-ray observations. Ever since then, the black hole has just been eating snacks.”

    The new study is a follow-on to previous Hubble observations that placed the age of the bubbles at 2 million years old.

    A black hole is a dense, compact region of space with a gravitational field so intense that neither matter nor light can escape. The supermassive black hole at the center of our galaxy has compressed the mass of 4.5 million sun-like stars into a very small region of space.

    Material that gets too close to a black hole is caught in its powerful gravity and swirls around the compact powerhouse until it eventually falls in. Some of the matter, however, gets so hot it escapes along the black hole’s spin axis, creating an outflow that extends far above and below the plane of a galaxy.

    The team’s conclusions are based on observations by Hubble’s Cosmic Origins Spectrograph (COS), which analyzed ultraviolet light from 47 distant quasars. Quasars are bright cores of distant active galaxies.


    NASA Hubble Cosmic Origins Spectrograph

    Imprinted on the quasars’ light as it passes through the Milky Way bubble is information about the speed, composition, and temperature of the gas inside the expanding bubble.

    The COS observations measured the temperature of the gas in the bubble at approximately 17,700 degrees Fahrenheit. Even at those sizzling temperatures, this gas is much cooler than most of the super-hot gas in the outflow, which is 18 million degrees Fahrenheit, seen in gamma rays. The cooler gas seen by COS could be interstellar gas from our galaxy’s disk that is being swept up and entrained into the super-hot outflow. COS also identified silicon and carbon as two of the elements being swept up in the gaseous cloud. These common elements are found in most galaxies and represent the fossil remnants of stellar evolution.

    The cool gas is racing through the bubble at 2 million miles per hour. By mapping the motion of the gas throughout the structure, the astronomers estimated that the minimum mass of the entrained cool gas in both bubbles is equivalent to 2 million suns. The edge of the northern bubble extends 23,000 light-years above the galaxy.

    “We have traced the outflows of other galaxies, but we have never been able to actually map the motion of the gas,” Bordoloi said. “The only reason we could do it here is because we are inside the Milky Way. This vantage point gives us a front-row seat to map out the kinematic structure of the Milky Way outflow.”

    The new COS observations build and expand on the findings of a 2015 Hubble study by the same team, in which astronomers analyzed the light from one quasar that pierced the base of the bubble.

    “The Hubble data open a whole new window on the Fermi Bubbles,” said study co-author Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland. “Before, we knew how big they were and how much radiation they emitted; now we know how fast they are moving and which chemical elements they contain. That’s an important step forward.”

    The Hubble study also provides an independent verification of the bubbles and their origin, as detected by X-ray and gamma-ray observations.

    “This observation would be almost impossible to do from the ground because you need ultraviolet spectroscopy to detect the fingerprints of these elements, which can only be done from space,” Bordoloi said. “Only with COS do you have the wavelength coverage, the sensitivity, and the spectral resolution coverage to make this observation.”

    The Hubble results appeared in the January 10, 2017, edition of The Astrophysical Journal.

    See the full article here .

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

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  • richardmitnick 9:35 am on February 23, 2017 Permalink | Reply
    Tags: , Sag A*,   

    From Universe Today: “Get Ready for the First Pictures of a Black Hole’s Event Horizon” 

    universe-today

    Universe Today

    22 Feb , 2017
    Evan Gough

    1
    NASA’s Spitzer Space Telescope captured this stunning infrared image of the center of the Milky Way Galaxy, where the black hole Sagitarrius A resides. Image: NASA/JPL-Caltech

    It might sound trite to say that the Universe is full of mysteries. But it’s true.

    Chief among them are things like Dark Matter, Dark Energy, and of course, our old friends the Black Holes. Black Holes may be the most interesting of them all, and the effort to understand them—and observe them—is ongoing.

    That effort will be ramped up in April, when the Event Horizon Telescope (EHT) attempts to capture our first image of a Black Hole and its event horizon. The target of the EHT is none other than Sagittarius A, the monster black hole that lies in the center of our Milky Way Galaxy. Though the EHT will spend 10 days gathering the data, the actual image won’t be finished processing and available until 2018.

    The EHT is not a single telescope, but a number of radio telescopes around the world all linked together. The EHT includes super-stars of the astronomy world like the Atacama Large Millimeter Array (ALMA) as well as lesser known ‘scopes like the South Pole Telescope (SPT.) Advances in very-long-baseline-interferometry (VLBI) have made it possible to connect all these telescopes together so that they act like one big ‘scope the size of Earth.

    The combined power of all these telescopes is essential because even though the EHT’s target, Sagittarius A, has over 4 million times the mass of our Sun, it’s 26,000 light years away from Earth. It’s also only about 20 million km across. Huge but tiny.

    The EHT is impressive for a number of reasons. In order to function, each of the component telescopes is calibrated with an atomic clock. These clocks keep time to an accuracy of about a trillionth of a second per second. The effort requires an army of hard drives, all of which will be transported via jet-liner to the Haystack Observatory at MIT for processing. That processing requires what’s called a grid computer, which is a sort of virtual super-computer comprised of 800 CPUs.

    But once the EHT has done its thing, what will we see? What we might see when we finally get this image is based on the work of three big names in physics: Einstein, Schwarzschild, and Hawking.

    2
    A simulation of what the EHT might show us. Image: Event Horizon Telescope Organization

    As gas and dust approach the black hole, they speed up. They don’t just speed up a little, they speed up a lot, and that makes them emit energy, which we can see. That would be the crescent of light in the image above. The black blob would be a shadow cast over the light by the hole itself.

    Einstein didn’t exactly predict the existence of Black Holes, but his theory of general relativity did. It was the work of one of his contemporaries, Karl Schwarzschild, that actually nailed down how a black hole might work. Fast forward to the 1970s and the work of Stephen Hawking, who predicted what’s known as Hawking Radiation.

    Taken together, the three give us an idea of what we might see when the EHT finally captures and processes its data.

    Einstein’s general relativity predicted that super massive stars would warp space-time enough that not even light could escape them. Schwarzschild’s work was based on Einstein’s equations and revealed that black holes will have event horizons. No light emitted from inside the event horizon can reach an outside observer. And Hawking Radiation is the theorized black body radiation that is predicted to be released by black holes.

    The power of the EHT will help us clarify our understanding of black holes enormously. If we see what we think we’ll see, it confirms Einstein’s Theory of General Relativity, a theory which has been confirmed observationally over and over. If EHT sees something else, something we didn’t expect at all, then that means Einstein’s General Relativity got it wrong. Not only that, but it means we don’t really understand gravity.

    In physics circles they say that it’s never smart to bet against Einstein. He’s been proven right time and time again. To find out if he was right again, we’ll have to wait until 2018.

    Event Horizon Telescope Array

    Event Horizon Telescope map

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

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

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

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    See the full article here .

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  • richardmitnick 3:16 pm on February 16, 2017 Permalink | Reply
    Tags: , , Sag A*   

    From BBC: “Event Horizon Telescope ready to image black hole” 

    BBC
    BBC

    2.16.17
    Jonathan Amos

    1
    The EHT team has produced simulations of what Einstein’s theories predict the hole should look like. Hotaka Shiokawa/CFA/HARVARD

    Scientists believe they are on the verge of obtaining the first ever picture of a black hole.

    They have built an Earth-sized “virtual telescope” by linking a large array of radio receivers – from the South Pole, to Hawaii, to the Americas and Europe.

    There is optimism that observations to be conducted during 5-14 April could finally deliver the long-sought prize.

    In the sights of the so-called “Event Horizon Telescope” will be the monster black hole at the centre of our galaxy.

    Here is the Event Horizon Telescope Array

    Event Horizon Telescope map

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

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

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

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

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

    Although never seen directly, this object, catalogued as Sagittarius A*, has been determined to exist from the way it influences the orbits of nearby stars.

    These race around a point in space at many thousands of km per second, suggesting the hole likely has a mass of about four million times that of the Sun.

    But as colossal as that sounds, the “edge” of the black hole – the horizon inside which an immense gravity field traps all light – may be no more than 20 million km or so across.

    And at a distance of 26,000 light-years from Earth, this makes Sagittarius A* a tiny pinprick on the sky.

    The Event Horizon Telescope (EHT) team is nonetheless bullish.

    “There’s great excitement,” said project leader Sheperd Doeleman from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

    “We’ve been fashioning our virtual telescope for almost two decades now, and in April we’re going to make the observations that we think have the first real chance of bringing a black hole’s event horizon into focus,” he told BBC News.

    EHT map

    2
    The eventual EHT array will have 12 widely spaced participating radio facilities

    The EHT’s trick is a technique called very long baseline array interferometry (VLBI).

    This combines a network of widely spaced radio antennas to mimic a telescope aperture that can produce the resolution necessary to perceive a pinprick on the sky.

    The EHT is aiming initially to get down to 50 microarcseconds. Team-members talk in analogies, describing the sharpness of vision as being the equivalent of seeing something the size of a grapefruit on the surface of the Moon.

    They emphasise the still complex years of work ahead, but also trail the prospect of an imminent breakthrough.

    The scientists certainly have an expectation of what they ought to see, if successful.

    Simulations rooted in Einstein’s equations predict a bright ring of light fringing a dark feature.

    The light would be the emission coming from gas and dust accelerated to high speed and torn apart just before disappearing into the hole.

    The dark feature would be the shadow the hole casts on this maelstrom.

    “Now, it could be that we will see something different,” Doeleman said.

    “As I’ve said before, it’s never a good idea to bet against Einstein, but if we did see something that was very different from what we expect we would have to reassess the theory of gravity.

    “I don’t expect that is going to happen, but anything could happen and that’s the beauty of it.”

    Over the years, more and more radio astronomy facilities have joined the project. A key recent addition is the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

    Its extraordinary state-of-the-art technology has at a stroke increased the EHT’s sensitivity by a factor of 10. Hence, the optimism ahead of April.

    Even so, scientists have had to install special equipment at all the radio facilities involved in the observations.

    This includes big hard drives to store colossal volumes of data, and atomic clocks to precisely timestamp it all.

    Nothing happens on the spot – the hard drives must first be flown to a large computing facility at MIT Haystack Observatory in Westford, just outside Boston, Massachusetts.

    “Our hard-drive modules hold the capacity of about 100 standard laptops,” said Haystack’s Vincent Fish.

    “We have multiple modules at each telescope and we have numerous telescopes in the array. So, ultimately, we’re talking about 10,000 laptops of data.”

    It is in Haystack’s correlator computer that the synthesis will begin.

    Some very smart imaging algorithms have had to be developed to make sense of the EHT’s observations, but it will not be a quick result.

    It could be the end of the year, perhaps the start of 2018, before the team releases an image in public.

    3
    All the data from the telescopes will be brought to MIT Haystack to be ingested in its correlator computer.

    Looking to the future, the scientists are already thinking about how to extend their techniques.

    For example, the matter closest to the event horizon and about to disappear into Sagittarius A* should take about 30 minutes to complete an orbit.

    Katie Bouman, from MIT’s Computer Science and Artificial Intelligence Laboratory, thinks it might be possible to capture this movement.

    “We want to push boundaries and to try to make movies from the data,” she told BBC News.

    “Maybe we can actually see some of the gas flowing around the black hole. That’s really the next stage of what we’re trying to accomplish with these imaging algorithms.”

    First and foremost, the team needs good weather at the participating observing stations in April.

    The strategy is to view the galactic centre at a wavelength of 1.3mm (230GHz). This has the best chance of piercing any obscuring gas and dust in the vicinity of the black hole. But if there is too much water vapour above the array’s receivers, the EHT will struggle even to see through Earth’s atmosphere.

    Just getting a resolved view of Sagittarius A* would be a remarkable triumph in itself. But the real objective here is to use the imaging capability to go test aspects of general relativity.

    If there are flaws to be found in Einstein’s ideas – and scientists suspects there are more complete explanations of gravity out there waiting to be discovered – then it is in the extreme environment of black holes that limitations should be exposed.

    See the full article here .

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  • richardmitnick 3:02 pm on August 28, 2016 Permalink | Reply
    Tags: , , , , , Sag A*,   

    From SEEKER: “The Race to See Our Supermassive Black Hole” 

    Seeker bloc

    SEEKER

    May 26, 2016 [Article brought forward by ESO]
    No writer credit found

    Using the power of interferometry, two astronomical projects are, for the first time, close to directly observing the black hole in the center of the Milky Way.

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

    There’s a monster living in the center of the galaxy.

    We know the supermassive black hole is there by tracking the motions of stars and gas clouds that orbit an invisible point. That point exerts an overwhelming tidal influence on all objects that get trapped in its gravitational domain and this force can be measured through stellar orbits to calculate its mass.

    It certainly isn’t the biggest black hole in the universe, but it isn’t the smallest either, it “weighs in” at an incredible 4 million times the mass of our sun.

    But this black hole behemoth, called Sagittarius A*, is over 20,000 light-years from Earth making direct observations, before now, nigh-on impossible. Despite its huge mass, the black hole is minuscule when seen from Earth; a telescope with an unprecedented angular resolution is needed.

    Though we already know a lot about Sagittarius A* from indirect observations, seeing is believing and there’s an international race, using the world’s most powerful observatories and sophisticated astronomical techniques, to zoom-in on the Milky Way’s black hole. This won’t only prove it’s really there, but it will reveal a region where space-time is so warped that we will be able to make direct tests of general relativity in the strongest gravity environment known to exist in the universe.

    The Event Horizon Telescope and GRAVITY

    A huge global effort is currently under way to link a network of global radio telescopes to create a virtual telescope that will span the width of our planet. Using the incredible power of interferometry, astronomers can combine the light from many distant radio antennae and collect it at one point, to mimic one large radio antenna spanning the globe.

    Event Horizon Telescope Array

    Event Horizon Telescope map
    Event Horizon Telescope map

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

    ESO/APEX
    Atacama Pathfinder EXperiment (APEX)

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    Future Array/Telescopes

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

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    This effort is known as the Event Horizon Telescope (EHT) and it is hoped the project will be able to attain the angular resolution and spatial definition required to soon produce its first radio observations of the bright ring just beyond Sagittarius A*’s event horizon — the point surrounding a black hole where nothing, not even light, can escape.

    However, another project has the same goal in mind, but it’s not going to observe in radio wavelengths, it’s going to stare deep into the galactic core to seek out optical and infrared light coming from Sagittarius A* and it just needs one observatory to make this goal a reality.

    1
    The ESO Very Large Telescope located atop Cerro Paranal in Chile. Ian O’Neill

    The GRAVITY instrument is currently undergoing commissioning at the ESO’s Very Large Telescope at Paranal Observatory high in the Atacama Desert in Chile (at an altitude of over 2,600 meters or 8,300 ft) and it will also use the power of interferometry to resolve our supermassive black hole. But rather than connecting global observatories like the EHT, GRAVITY will combine the light of the four 8 meter telescopes of the VLT Interferometer (collectively known as the VLTI) to create a “virtual” telescope measuring the distance between each individual telescope.

    ESO GRAVITY insrument
    ESO GRAVITY insrument

    “By doing this you can reach the same resolution and precision that you would get from a telescope that has a size, in this case, of roughly a hundred meters, simply because these eight meter-class telescopes are separated by roughly one hundred meters,” astronomer Oliver Pfuhl, of Max Planck Institute for Extraterrestrial Physics, Germany, told DNews. “If you combine the light from those you reach the same resolution as a virtual telescope of a hundred meters would have.”

    Strong Gravity Environment

    When GRAVITY is online it will be used to track features just outside Sagittarius A*’s event horizon.

    “For about ten years, we’ve known that this black hole is actually not black. Once in awhile it flares, so we see it brightening and darkening,” he said. This flaring is matter falling into the event horizon, generating a powerful flash of energy. The nature of these flares are poorly understood, but the instrument should be able to track this flaring material as it rapidly orbits the event horizon and fades away. These flares will also act as tracers, helping us see the structure of space-time immediately surrounding a black hole for the first time.

    2
    One of the four Very Large Telescope domes fires its new four-laser adaptive optics system. GRAVITY will make use of adaptive optics to improve observations of Sagittarius A* by compensating for the effects of atmospheric turbulence. ESO

    “Our goal is to measure these motions. We think that what we see as this flaring is actually gas which spirals into the black hole. This brightening and darkening is essentially the gas, when it comes too close to the black hole, the strong tidal forces make it heat up,” said Pfuhl.

    “If we can study these motions which happen so close to the black hole, we have a direct probe of the space time close to the black hole. In this way we have a direct test of general relativity in one of the most extreme environments which you can find in the universe.”

    While GRAVITY will be able to track these flaring events very close to the black hole, the Event Horizon Telescope will see the shadow, or silhouette, of the dark event horizon surrounded by radio wave emissions. Both projects will be able to measure different components of the region directly surrounding the event horizon, so combined observations in optical and radio wavelengths will complement one other.

    It just so happens that the Atacama Large Millimeter/submillimeter Array (ALMA), the largest radio observatory on the planet — also located in the Atacama Desert — will also be added to the EHT.

    “The Event Horizon Telescope will combine ALMA with telescopes around the world like Hawaii and other locations, and with that power you can look at really fine details especially in the black hole in the center of our galaxy and perhaps in some really nearby other galaxies that also have black holes in their centers,” ESO astronomer Linda Watson told DNews.

    3
    The ALMA antenna in a clustered formation on Chajnantor plateau during the #MeetESO event on May 11, 2016. The extreme location of the observatory can produce unpredictable weather and, as depicted here, a blizzard descended on the plateau cutting the visit short.
    Ian O’Neill

    ALMA itself is an interferometer combining the collecting power of 66 radio antennae located atop Chajnantor plateau some 5,000 meters (16,400 ft) in altitude. Watson uses ALMA data to study the cold dust in interstellar space, but when added to the EHT, its radio-collecting power will help us understand the dynamics of the environment surrounding Sagittarius A*.

    “ALMA’s an interferometer with 66 antennas, (the EHT) will treat ALMA as just one telescope and will combine it with other telescopes around the world to be another interferometer,” she added.

    Black Hole Mysteries

    Many black holes are thought to possess an accretion disk of swirling gas and dust. ALMA, when combined with the EHT, will be able to measure this disk’s structure, speed and direction of motion. Lacking direct observations, many of these characteristics have only been modeled by computer simulations or inferred from indirect observations. We’re about to enter an era when we can truly get to answer some of the biggest mysteries surrounding black hole dynamics.

    “The first thing we want to see is we want to understand how accretion works close to the black hole,” said Pfuhl. “This is also true for the Event Horizon Telescope. Another thing we want to learn is does our black hole have spin? That means, does it rotate?”

    Though the EHT and GRAVITY are working at different wavelengths, observing phenomena around Sagittarius A* will reveal different things about the closest supermassive black hole to Earth. By extension it is hoped that we may observe smaller black holes in our galaxy and other supermassive black holes in neighboring galaxies.

    3
    Computer simulation of what theoretical physiicists expect to see with the EHT — a round, dark disk surrounded by radio emissions.
    Avery E. Broderick/Univ. of Waterloo/Perimeter Institute (screenshot from the Convergence meeting)

    But as we patiently wait for the first direct observations of the black hole monster lurking in the center of our galaxy, an event that some scientists say will be as historic as the “Pale Blue Dot” photo of Earth as captured by Voyager 1 in 1990, it’s hard not to wonder which project will get there first.

    “I think it’s a very tight race,” said Pfuhl. “Let’s see.”

    See the full article here .

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  • richardmitnick 3:31 pm on July 22, 2016 Permalink | Reply
    Tags: , , , Sag A*   

    From Spitzer: “Seeing the Milky Way’s Giant Black Hole with New Eyes” 

    NASA Spitzer Telescope

    Spitzer

    07.21.16

    1

    At the center of our Milky Way galaxy lies a cosmic beast called Sagittarius A*. This supermassive black hole packs about four million sun-masses into a volume roughly the size of our solar system.

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

    Recently, NASA’s Spitzer Space Telescope began exploring this exotic object. The telescope has observed a great many cosmic phenomena, from galaxy clusters to stellar nurseries during its 13-year career, but the black hole at the center of the Milky Way was never a part of the spacecraft designers’ plans.

    “A decade ago, no one would have taken you seriously if you had mentioned doing science like this with Spitzer,” said Varoujan Gorjian, a research astronomer at NASA’s Jet Propulsion Laboratory in Pasadena, California, who studies supermassive black holes. “We are very pleased that, because of its recent sensitivity boost, Spitzer can now serve as another arrow in our quiver when targeting the black hole at the heart of the Milky Way.”

    The sensitivity boost involves an observing mode originally intended to study exoplanets. It has given Spitzer the unexpected capability to monitor infrared flares emitted by this monster black hole, known as Sagittarius A* (pronounced “Sagittarius-A-star”). In a trial run in December 2013, Spitzer took an unprecedented 23-hour exposure. Though other telescopes have observed variability in the Sagittarius A* region, Spitzer was the first to observe it at the wavelength of 4.5 microns.

    Building on that success, a fresh round of observations has just been completed, with Spitzer observing Sagittarius A* simultaneously with NASA’s Chandra X-ray Observatory and the ground-based ALMA and SMA microwave observatories .

    NASA/Chandra Telescope
    NASA/Chandra Telescope

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

    SMA Submillimeter Array
    CfA SMA Submillimeter Array 8-element radio interferometer, Maunakea, Hawaii, USA

    Spitzer’s contributions will aid ongoing efforts in understanding why the Milky Way’s big black hole accretes, or gobbles up, material so calmly, compared to black holes in similar galaxies.

    “We can now use Spitzer to study the emission from the innermost regions of the accretion flow onto the black hole, near the event horizon,” said Joseph Hora, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, and the lead author of a 2014 study in The Astrophysical Journal reporting Spitzer’s Sagittarius A* observations. The observing project was led by Giovanni Fazio, also of CfA, with collaborators including the University of California, Los Angeles (UCLA) Galactic Center group led by Andrea Ghez.

    Eyeing a monster

    Located 26,000 light years away, Sagittarius A* is completely obscured by dust. Radio telescopes on Earth were the first to hone in on Sagittarius A* because radio waves freely pass through this dust, as well as our planet’s atmosphere. Other critical insights into Sagittarius A* have since come from the Chandra telescope, which scoops up dust-penetrating X-rays in space.

    The study of Sagittarius A* in infrared light has been knottier, but hugely successful. Although infrared light can also penetrate dust, only certain infrared wavelengths transmit through Earth’s atmosphere. Plus, these sorts of observations must contend with infrared light emitted by both the atmosphere and telescopic equipment itself.

    Despite these obstacles, starting in the mid-1990s, the 10-meter Keck Telescope in Hawaii tracked the orbits of stars (in infrared) whipping about an unseen, colossal mass emitting radio waves and X-rays at the center of our galaxy.

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

    Ground-based observations more recently captured an outburst of infrared light from Sagittarius A* itself, presumably as it wolfed down some matter that had strayed too close. Researchers desperately want more of these sorts of observations of Sagittarius A*’s variability. Comparing these data in additional wavelengths to radio waves and X-rays will help them construct a thorough model for just how Sagittarius A* interacts with its cosmic environment.

    Encouraged by the Keck results, Fazio and colleagues began considering using Spitzer’s infrared camera to investigate Sagittarius A*. The odds did not look good, though. Because Spitzer’s resolution cannot match that of the Keck telescope, the light from Sagittarius A* would be blended with the light of the many bright stars in the black hole’s central galactic vicinity. Tracking its variability therefore seemed out of Spitzer’s reach.

    Unleashing Spitzer’s full power

    Fortunately, NASA engineers in the early 2010s were already seeking to increase Spitzer’s stability and targeting — essentially, its ability to pick one spot in the universe and stare at it with minimal wobbling. The intended purpose of this upgrade was to let Spitzer point fixedly at a star and watch for miniscule dimming as an exoplanet crossed, or transited. Such transits reveal an exoplanet’s size, as well as clues about its atmospheric composition.

    Planet transit. NASA/Ames
    Planet transit. NASA/Ames

    To achieve the necessary stability for exoplanet studies, Spitzer’s engineers took three steps. First, in October 2010, they figured out an intermittent wobble within Spitzer stemmed from an internal heater switching on for an hour to warm a battery. The engineers managed to cut the wobble in half while preserving the battery by reducing the heater to 30-minute cycles. Next, in September 2011, the engineers repurposed a “Peak-Up” camera, used during Spitzer’s early, cryogenic mission. The Peak-Up Camera can precisely place infrared light onto an exact part of a pixel in Spitzer’s infrared camera. Engineers also mapped an individual pixel for its “sweet spot” that returns the most stable observations.

    With these refinements in place, Spitzer could theoretically look for tiny brightness changes due to Sagittarius A* without having to isolate the object from its nearby stars. Because those neighboring stars do not vary much in brightness, any variations seen in the combined light from that region can be chalked up to activity by Sagittarius A*. Remarkably, Spitzer can detect a change of a few tenths of a percent in infrared light emanating from the Milky Way’s core.

    “When Sagittarius A* flares, it produces an increase in light in the infrared range. If the flare is bright enough, then Spitzer sees that as light poured on top of what’s coming at the telescope already,” said Gorjian.

    With a view undisturbed by Earth’s atmosphere and the ability to monitor Sagittarius A* for more than 20 hours straight, Spitzer is an important extension of ground-based infrared observations of the black hole.

    “With Spitzer, you can monitor longer, and that’s critical in determining what is causing the variability in Sagittarius A*,” said Hora.

    Spitzer’s upcoming observations this summer in tandem with Chandra will gather infrared and X-ray emission to probe material very close to the Sagittarius A* black hole itself, helping test models of what causes the flare. It’s a whole new science objective for Spitzer, which continues to surprise and delight so many years after its launch in the summer of 2003.

    See the full article here .

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    The Spitzer Space Telescope is a NASA mission managed by the Jet Propulsion Laboratory located on the campus of the California Institute of Technology and part of NASA’s Infrared Processing and Analysis Center.

    NASA image

    NASA JPL Icon

     
  • richardmitnick 8:14 am on June 1, 2016 Permalink | Reply
    Tags: , , , , , Sag A*   

    From Seeker at Discovery: “The Race to See Our Supermassive Black Hole” 

    Discovery News
    Discovery News

    1

    May 26, 2016
    No writer credit found.

    Using the power of interferometry, two astronomical projects are, for the first time, close to directly observing the black hole in the center of the Milky Way.

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

    There’s a monster living in the center of the galaxy.

    We know the supermassive black hole is there by tracking the motions of stars and gas clouds that orbit an invisible point. That point exerts an overwhelming tidal influence on all objects that get trapped in its gravitational domain and this force can be measured through stellar orbits to calculate its mass.

    ESO VLT new laser
    ESO VLT new laser

    It certainly isn’t the biggest black hole in the universe, but it isn’t the smallest either, it “weighs in” at an incredible 4 million times the mass of our sun.

    But this black hole behemoth, called Sagittarius A*, is over 20,000 light-years from Earth making direct observations, before now, nigh-on impossible. Despite its huge mass, the black hole is minuscule when seen from Earth; a telescope with an unprecedented angular resolution is needed.

    Though we already know a lot about Sagittarius A* from indirect observations, seeing is believing and there’s an international race, using the world’s most powerful observatories and sophisticated astronomical techniques, to zoom-in on the Milky Way’s black hole. This won’t only prove it’s really there, but it will reveal a region where space-time is so warped that we will be able to make direct tests of general relativity in the strongest gravity environment known to exist in the universe.

    The Event Horizon Telescope and GRAVITY

    A huge global effort is currently under way to link a network of global radio telescopes to create a virtual telescope that will span the width of our planet. Using the incredible power of interferometry, astronomers can combine the light from many distant radio antennae and collect it at one point, to mimic one large radio antenna spanning the globe.

    A huge global effort is currently under way to link a network of global radio telescopes to create a virtual telescope that will span the width of our planet. Using the incredible power of interferometry, astronomers can combine the light from many distant radio antennae and collect it at one point, to mimic one large radio antenna spanning the globe.

    This effort is known as the Event Horizon Telescope (EHT) and it is hoped the project will be able to attain the angular resolution and spatial definition required to soon produce its first radio observations of the bright ring just beyond Sagittarius A*’s event horizon — the point surrounding a black hole where nothing, not even light, can escape.

    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

    Future Array/Telescopes

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

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    However, another project has the same goal in mind, but it’s not going to observe in radio wavelengths, it’s going to stare deep into the galactic core to seek out optical and infrared light coming from Sagittarius A* and it just needs one observatory to make this goal a reality.

    The GRAVITY instrument is currently undergoing commissioning at the ESO’s Very Large Telescope at Paranal Observatory high in the Atacama Desert in Chile (at an altitude of over 2,600 meters or 8,300 ft) and it will also use the power of interferometry to resolve our supermassive black hole.

    ESO GRAVITY insrument
    ESO GRAVITY insrument

    But rather than connecting global observatories like the EHT, GRAVITY will combine the light of the four 8 meter telescopes of the VLT Interferometer (collectively known as the VLTI) to create a “virtual” telescope measuring the distance between each individual telescope.

    ESO VLTI image
    ESO VLTI image

    “By doing this you can reach the same resolution and precision that you would get from a telescope that has a size, in this case, of roughly a hundred meters, simply because these eight meter-class telescopes are separated by roughly one hundred meters,” astronomer Oliver Pfuhl, of Max Planck Institute for Extraterrestrial Physics, Germany, told DNews. “If you combine the light from those you reach the same resolution as a virtual telescope of a hundred meters would have.”

    Strong Gravity Environment

    When GRAVITY is online it will be used to track features just outside Sagittarius A*’s event horizon.

    “For about ten years, we’ve known that this black hole is actually not black. Once in awhile it flares, so we see it brightening and darkening,” he said. This flaring is matter falling into the event horizon, generating a powerful flash of energy. The nature of these flares are poorly understood, but the instrument should be able to track this flaring material as it rapidly orbits the event horizon and fades away. These flares will also act as tracers, helping us see the structure of space-time immediately surrounding a black hole for the first time.

    Our goal is to measure these motions. We think that what we see as this flaring is actually gas which spirals into the black hole. This brightening and darkening is essentially the gas, when it comes too close to the black hole, the strong tidal forces make it heat up,” said Pfuhl.

    “If we can study these motions which happen so close to the black hole, we have a direct probe of the space time close to the black hole. In this way we have a direct test of general relativity in one of the most extreme environments which you can find in the universe.”

    While GRAVITY will be able to track these flaring events very close to the black hole, the Event Horizon Telescope will see the shadow, or silhouette, of the dark event horizon surrounded by radio wave emissions. Both projects will be able to measure different components of the region directly surrounding the event horizon, so combined observations in optical and radio wavelengths will complement one other.

    It just so happens that the Atacama Large Millimeter/submillimeter Array (ALMA), the largest radio observatory on the planet — also located in the Atacama Desert — will also be added to the EHT.

    “The Event Horizon Telescope will combine ALMA with telescopes around the world like Hawaii and other locations, and with that power you can look at really fine details especially in the black hole in the center of our galaxy and perhaps in some really nearby other galaxies that also have black holes in their centers,” ESO astronomer Linda Watson told DNews.

    ALMA itself is an interferometer combining the collecting power of 66 radio antennae located atop Chajnantor plateau some 5,000 meters (16,400 ft) in altitude. Watson uses ALMA data to study the cold dust in interstellar space, but when added to the EHT, its radio-collecting power will help us understand the dynamics of the environment surrounding Sagittarius A*.

    “ALMA’s an interferometer with 66 antennas, (the EHT) will treat ALMA as just one telescope and will combine it with other telescopes around the world to be another interferometer,” she added.

    Black Hole Mysteries

    Many black holes are thought to possess an accretion disk of swirling gas and dust. ALMA, when combined with the EHT, will be able to measure this disk’s structure, speed and direction of motion. Lacking direct observations, many of these characteristics have only been modeled by computer simulations or inferred from indirect observations. We’re about to enter an era when we can truly get to answer some of the biggest mysteries surrounding black hole dynamics.

    “The first thing we want to see is we want to understand how accretion works close to the black hole,” said Pfuhl. “This is also true for the Event Horizon Telescope. Another thing we want to learn is does our black hole have spin? That means, does it rotate?”

    Though the EHT and GRAVITY are working at different wavelengths, observing phenomena around Sagittarius A* will reveal different things about the closest supermassive black hole to Earth. By extension it is hoped that we may observe smaller black holes in our galaxy and other supermassive black holes in neighboring galaxies.

    But as we patiently wait for the first direct observations of the black hole monster lurking in the center of our galaxy, an event that some scientists say will be as historic as the “Pale Blue Dot” photo of Earth as captured by Voyager 1 in 1990, it’s hard not to wonder which project will get there first.

    “I think it’s a very tight race,” said Pfuhl. “Let’s see.”

    See the full article here .

    Please help promote STEM in your local schools.

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  • richardmitnick 10:10 pm on September 23, 2015 Permalink | Reply
    Tags: , , , Sag A*   

    From Chandra- “Sagittarius A*: Milky Way’s Black Hole Shows Signs of Increased Chatter” 

    NASA Chandra

    September 23, 2015

    Temp 1
    Credit NASA/CXC/MPE/G.Ponti et al; Illustration: NASA/CXC/M.Weiss
    Release Date September 23, 2015

    A long monitoring campaign of the Milky Way’s supermassive black hole has revealed some unusual activity. Typically relatively quiet, the black hole (called Sagittarius A*) had an increase in X-ray flares in mid-2014.

    2
    This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes.

    The timing of this surge coincided with the close passage of the mysterious G2 object near the black hole. Astronomers will continue to observe the black hole to ascertain the true nature of the increased X-ray activity.

    Three orbiting X-ray telescopes have been monitoring the supermassive black hole at the center of the Milky Way galaxy for the last decade and a half to observe its behavior, as explained in our latest press release. This long monitoring campaign has revealed some new changes in the patterns of this 4-million-solar-mass black hole known as Sagittarius A* (Sgr A*).

    The bottom panel of this graphic is a view of the region around Sgr A* where red, green, and blue represent low, medium, and high-energy X-rays detected by NASA’s Chandra X-ray Observatory. Sgr A* itself is not visible in this image, but is embedded in the white dot at the end of the arrow. The other two telescopes involved in the 15 years of X-ray observations were ESA’s XMM-Newton and NASA’s Swift Gamma Ray Burst Explorer, but their data are not included in this image.

    ESA XMM Newton
    ESA XMM-Newton

    NASA SWIFT Telescope
    NASA/ Swift

    Within the past year, the usually quiet black hole has shown an increased level of X-ray flares over its typical rate. This surge in X-ray flares coincides with the passage close to Sgr A* of a mysterious object called G2. Astronomers have been tracking G2 for years [Andrea Ghez, UCLA], originally thinking it was an extended cloud of gas and dust. However, after passing close to Sgr A* in late 2013 its appearance did not change much, apart from being slightly stretched by the gravity of the black hole. This led to new theories that G2 was not a gas cloud, but instead a star or pair of stars within an extended dusty cocoon.

    If the G2 explanation does explain the recent rise in X-ray flares, it would be the first sign of excess material falling onto the black hole because of the cloud’s close passage. Some gas would likely have been stripped off the cloud, and captured by the gravity of Sgr A*. It then could have started interacting with hot material flowing towards the black hole, resulting in an enhanced feeding rate and the production of X-ray flares. This scenario is depicted in the artist’s illustrations found in the upper two panels of the graphic.

    While the timing of G2’s passage with the surge in X-rays from Sgr A* is intriguing, it is not yet an open-and-shut case. That is because astronomers see other black holes that appear to have behavior similar to the most recent increase of activity from Sgr A*. Therefore, it’s possible this increased chatter from Sgr A* may be a common trait among supermassive black holes and unrelated to G2. Instead, it could represent, for example, a change in the strength of winds from nearby massive stars that are feeding the black hole.

    The analysis included 150 Chandra and XMM-Newton observations pointed at the center of the Milky Way over the last 15 years, extending from September 1999 to November 2014. An increase in the rate and brightness of bright flares from Sgr A* occurred after mid-2014, several months after the closest approach of G2 to the huge black hole. The newest set of Chandra, XMM and Swift observations, obtained between August 30 and October 2014, revealed six bright flares within about three days, while an average of only 0.8 bright flares was expected.

    A paper on these findings has been accepted by the Monthly Notices of the Royal Astronomical Society and a preprint is available online. The authors of this study were Gabriele Ponti (Max Planck Institute for Extraterrestrial Physics), Barbara De Marco (Max Planck), Mark Morris (University of California, Los Angeles), Andrea Merloni (Max Planck), Teo Muñoz-Darias (University of La Laguna, Spain), Maica Clavel (CEA Saclay, France), Darryl Haggard (Amherst College), Shuo Zhang (Columbia University), Kirpal Nandra (Max Planck), Stefan Gillassen (Max Planck), Kenji Mori (Columbia), Joseph Nielsen (Massachusetts Institute of Technology), Nanda Rea (University of Amsterdam), Natalie Degenaar (University of Cambridge), Regis Terrier (University of Paris), and Andrea Goldwurm (CEA Saclay).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
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