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  • richardmitnick 5:06 pm on March 29, 2019 Permalink | Reply
    Tags: , , , SgrA*, SO-2 and SO-38 circle SGR A*Image UCLA Galactic Center Groupe via S. Sakai and Andrea Ghez at Keck Observatory   

    From Science News: “4 things we’ll learn from the first closeup image of a black hole” 

    From Science News

    March 29, 2019
    Lisa Grossman

    Event Horizon Telescope data are giving scientists an image of the Milky Way’s behemoth.

    1
    FIRST LOOK The first image from the Event Horizon Telescope may show that the black hole at the center of our galaxy looks something like this simulation.

    The Event Horizon Telescope, a network of eight radio observatories spanning the globe, has set its sights on a pair of behemoths: Sagittarius A*, the supermassive black hole at the Milky Way’s center, and an even more massive black hole 53.5 million light-years away in galaxy Messier 87 (SN Online: 4/5/17).

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

    SgrA* NASA/Chandra supermassive black hole at the center of the Milky Way

    Sgr A* from ESO VLT

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

    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

    In April 2017, the observatories teamed up to observe the black holes’ event horizons, the boundary beyond which gravity is so extreme that even light can’t escape (SN: 5/31/14, p. 16). After almost two years of rendering the data, scientists are gearing up to release the first images in April.

    Here’s what scientists hope those images can tell us.

    What does a black hole really look like?

    Black holes live up to their names: The great gravitational beasts emit no light in any part of the electromagnetic spectrum, so they themselves don’t look like much.

    But astronomers know the objects are there because of a black hole’s entourage. As a black hole’s gravity pulls in gas and dust, matter settles into an orbiting disk, with atoms jostling one another at extreme speeds. All that activity heats the matter white-hot, so it emits X-rays and other high-energy radiation. The most voraciously feeding black holes in the universe have disks that outshine all the stars in their galaxies (SN Online: 3/16/18).

    3
    TOO BIG, TOO SOON Supermassive black holes that are actively feeding on gas and dust, like the one shown in this artist’s rendition, have been spotted in the early universe — before they should have had time to grow. NAOJ.


    A CAMERA THE SIZE OF EARTH How did scientists take a picture of a black hole? Science News explains.

    The EHT’s image of the Milky Way’s Sagittarius A*, also called SgrA*, is expected to capture the black hole’s shadow on its accompanying disk of bright material. Computer simulations and the laws of gravitational physics give astronomers a pretty good idea of what to expect. Because of the intense gravity near a black hole, the disk’s light will be warped around the event horizon in a ring, so even the material behind the black hole will be visible.

    And the image will probably look asymmetrical: Gravity will bend light from the inner part of the disk toward Earth more strongly than the outer part, making one side appear brighter in a lopsided ring.

    Does general relativity hold up close to a black hole?

    The exact shape of the ring may help break one of the most frustrating stalemates in theoretical physics.

    The twin pillars of physics are Einstein’s theory of general relativity, which governs massive and gravitationally rich things like black holes, and quantum mechanics, which governs the weird world of subatomic particles. Each works precisely in its own domain. But they can’t work together.

    “General relativity as it is and quantum mechanics as it is are incompatible with each other,” says physicist Lia Medeiros of the University of Arizona in Tucson. “Rock, hard place. Something has to give.” If general relativity buckles at a black hole’s boundary, it may point the way forward for theorists.

    Since black holes are the most extreme gravitational environments in the universe, they’re the best environment to crash test theories of gravity. It’s like throwing theories at a wall and seeing whether — or how — they break. If general relativity does hold up, scientists expect that the black hole will have a particular shadow and thus ring shape; if Einstein’s theory of gravity breaks down, a different shadow.

    Medeiros and her colleagues ran computer simulations of 12,000 different black hole shadows that could differ from Einstein’s predictions. “If it’s anything different, [alternative theories of gravity] just got a Christmas present,” says Medeiros, who presented the simulation results in January in Seattle at the American Astronomical Society meeting. Even slight deviations from general relativity could create different enough shadows for EHT to probe, allowing astronomers to quantify how different what they see is from what they expect.


    CONSIDERING ALL POSSIBILITIES Physicists expect black holes to follow Einstein’s rules of general relativity, but it might be more interesting if they don’t. This computer simulation shows one possibility for how a black hole would look if it behaved unexpectedly.

    Do stellar corpses called pulsars surround the Milky Way’s black hole?

    Another way to test general relativity around black holes is to watch how stars careen around them. As light flees the extreme gravity in a black hole’s vicinity, its waves get stretched out, making the light appear redder. This process, called gravitational redshift, is predicted by general relativity and was observed near SgrA* last year (SN: 8/18/18, p. 12). So far, so good for Einstein.

    5
    BLACK HOLE SUN Einstein’s theory of gravity was upheld in measurements of a star that recently made a close pass by the supermassive black hole at the center of the Milky Way, as shown in this artist’s conception illustrating the star’s trajectory over the past few months.

    SO-2 and SO-38 circle SGR A*Image UCLA Galactic Center Groupe via S. Sakai and Andrea Ghez at Keck Observatory

    An even better way to do the same test would be with a pulsar, a rapidly spinning stellar corpse that sweeps the sky with a beam of radiation in a regular cadence that makes it appear to pulse (SN: 3/17/18, p. 4). Gravitational redshift would mess up the pulsars’ metronomic pacing, potentially giving a far more precise test of general relativity.

    “The dream for most people who are trying to do SgrA* science, in general, is to try to find a pulsar or pulsars orbiting” the black hole, says astronomer Scott Ransom of the National Radio Astronomy Observatory in Charlottesville, Va. “There are a lot of quite interesting and quite deep tests of [general relativity] that pulsars can provide, that EHT [alone] won’t.”

    Women in STEM – Dame Susan Jocelyn Bell Burnell

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

    Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

    Dame Susan Jocelyn Bell Burnell 2009

    Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

    Despite careful searches, no pulsars have been found near enough to SgrA* yet, partly because gas and dust in the galactic center scatters their beams and makes them difficult to spot. But EHT is taking the best look yet at that center in radio wavelengths, so Ransom and colleagues hope it might be able to spot some.

    “It’s a fishing expedition, and the chances of catching a whopper are really small,” Ransom says. “But if we do, it’s totally worth it.”

    How do some black holes make jets?

    Some black holes are ravenous gluttons, pulling in massive amounts of gas and dust, while others are picky eaters. No one knows why. SgrA* seems to be one of the fussy ones, with a surprisingly dim accretion disk despite its 4 million solar mass heft. EHT’s other target, the black hole in galaxy M87, is a voracious eater, weighing in at about 2.4 trillion solar masses. And it doesn’t just amass a bright accretion disk. It also launches a bright, fast jet of charged subatomic particles that stretches for about 5,000 light-years.

    “It’s a little bit counterintuitive to think a black hole spills out something,” says astrophysicist Thomas Krichbaum of the Max Planck Institute for Radio Astronomy in Bonn, Germany. “Usually people think it only swallows something.”

    Many other black holes produce jets that are longer and wider than entire galaxies and can extend billions of light-years from the black hole. “The natural question arises: What is so powerful to launch these jets to such large distances?” Krichbaum says. “Now with the EHT, we can for the first time trace what is happening.”

    EHT’s measurements of Messier 87’s black hole will help estimate the strength of its magnetic field, which astronomers think is related to the jet-launching mechanism. And measurements of the jet’s properties when it’s close to the black hole will help determine where the jet originates — in the innermost part of the accretion disk, farther out in the disk or from the black hole itself. Those observations might also reveal whether the jet is launched by something about the black hole itself or by the fast-flowing material in the accretion disk.

    Since jets can carry material out of the galactic center and into the regions between galaxies, they can influence how galaxies grow and evolve, and even where stars and planets form (SN: 7/21/18, p. 16).

    “It is important to understanding the evolution of galaxies, from the early formation of black holes to the formation of stars and later to the formation of life,” Krichbaum says. “This is a big, big story. We are just contributing with our studies of black hole jets a little bit to the bigger puzzle.”

    See the full article here .


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  • richardmitnick 12:43 pm on March 21, 2018 Permalink | Reply
    Tags: , , , , , , SgrA*   

    From astronomy.com: “The core of the Milky Way unveiled in clearest infrared image yet” 

    Astronomy magazine

    astronomy.com

    February 27, 2018 [Just now in social media.]
    Jake Parks

    1
    This new high-resolution map shows the magnetic field lines embedded in gas and dust around the supermassive black hole (Sagittarius A*) residing in the core of the Milky Way. Red areas show regions where warm dust particles and stars are emitting lots of infrared radiation (heat), while dark blue areas show cooler regions that lack pronounced warm and dusty filaments. E. Lopez-Rodriguez/NASA Ames/University of Texas at San Antonio.

    At the center of nearly every galaxy resides a gargantuan black hole. For the Milky Way, the supermassive black hole — dubbed Sagittarius A* — is so massive that its gravity flings stars around at speeds of up to 18.5 million miles (30 million kilometers) per hour.

    SgrA* NASA/Chandra


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

    In order to accelerate stars to these breakneck speeds, astronomers estimate that Sagittarius A* must be about 4 million times more massive than the Sun.

    With such a monstrous and intriguing object located in the center of our galaxy, you would think that astronomers know a great deal about it. However, thanks to the fact that the Milky Way is full of light-blocking gas and dust, many questions still remain about the structure and behavior of Sagittarius A*.

    In a paper published last month in the Monthly Notices of the Royal Astronomical Society, astronomers shed a bit of light on this black hole by producing a new high-resolution map that traces the magnetic field lines present within gas and dust swirling around Sagittarius A*. The team created the map, which is the first of its kind, by observing polarized infrared light that is emitted by warm, magnetically aligned dust grains.

    Because infrared light passes straight through the visual-light-blocking dust located between Earth and the Milky Way’s core, astronomers were able to view the area around Sagittarius A* much more clearly than would have been possible with other types of telescopes. Furthermore, since CanariCam combines infrared imaging with a device that preferentially filters polarized light associated with magnetic fields, the team was able to trace the magnetic field lines around Sagittarius A* in unprecedented detail.

    To create the detailed map, which spans about one light-year on each side of Sagittarius A*, the researchers used the CanariCam infrared camera on the Gran Telescopio Canarias (GTC), located on the island of La Palma, Spain. Because infrared light passes straight through the visual-light-blocking dust located between Earth and the Milky Way’s core, astronomers were able to view the area around Sagittarius A* much more clearly than would have been possible with other types of telescopes. Furthermore, since CanariCam combines infrared imaging with a device that preferentially filters polarized light associated with magnetic fields, the team was able to trace the magnetic field lines around Sagittarius A* in unprecedented detail.

    IAC CanariCam on the Gran Telescopio Canarias at Roque de los Muchachos Observatory island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    “Big telescopes like GTC, and instruments like CanariCam deliver real results,” said Pat Roche, a professor of astrophysics at The University of Oxford, in a press release. “We’re now able to watch material race around a black hole 25,000 light-years away, and for the first time see magnetic fields there in detail.”

    3
    This version of the map shows to what extent the light is polarized at various locations throughout the image. The longer a line is, the more the light is polarized. Sagittarius A*, our galaxy’s supermassive black hole, is located in the center of the image (0,0). Roche et al (MNRAS 2018)

    These new observations not only make for a wonderful image — the clearest infrared image of our galactic core to date — but also provide astronomers with vital information regarding the relationship between luminous stars and the filaments of gas and dust that stretch between them. One prominent feature in the map shows that dusty filaments connect some of the brightest stars in the center of the Milky Way despite incredibly strong stellar winds. The researchers believe that these filaments remain in place because they are bound by magnetic fields that permeate through the dust.

    Based on map, the team also thinks that a smaller magnetic field exists near the core of the Milky Way, and that the field gets stretched out as intervening filaments are pulled apart by gravity. The researchers point out that the filaments, which are several light-years long, seem to pool below (on the map) Sagittarius A*. The team believes that this likely marks a location where streams of gas and dust orbiting the black hole converge.

    Using the CanariCam on GTC, the researchers plan to continue probing the magnetic fields traced in dusty regions throughout our galaxy. Additionally, they hope to continue gathering more detailed observations of the core of the Milky Way to further study the magnetic field around Sagittarius A*. In particular, they would like to determine how the magnetic field interacts with clouds of dust and gas that orbit farther from the black hole, at distances of several light years.

    But for now, we’ll just have to be satisfied with the latest piece of the puzzle.

    [The work of Andrea Ghez deserves credit here.

    Andrea Mia Ghez is an American astronomer and professor in the Department of Physics and Astronomy at UCLA. In 2004, Discover magazine listed Ghez as one of the top 20 scientists in the United States who have shown a high degree of understanding in their respective fields. Ghez is a member of the UCLA Galactic Center Group

    Andrea Ghez, UCLA

    Andrea’s Favorite star SO-2

    Her current research involves using high spatial resolution imaging techniques, such as the adaptive optics system at the Keck telescopes, to study star-forming regions and the supermassive black hole at the center of the Milky Way known as Sagittarius A*. She uses the kinematics of stars near the center of the Milky Way as a probe to investigate this region. The high resolution of the Keck telescopes gave a significant improvement over the first major study of galactic center kinematics by Reinhard Genzel’s group.


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level, showing also NASA’s IRTF and NAOJ Subaru

    In 2004, Ghez was elected to the National Academy of Sciences. She has appeared in a long list of notable media presentations. The documentaries have been produced by organizations such as BBC, Discovery Channel, and The History Channel; in 2006 there was a presentation on Nova. She was identified as a Science Hero by The My Hero Project.]

    See the full article here .

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  • richardmitnick 6:19 pm on March 6, 2018 Permalink | Reply
    Tags: A Decade of Atmospheric Data Aids Black Hole Observers, , , , , , , , SgrA*   

    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 7:06 am on February 28, 2018 Permalink | Reply
    Tags: , , , , , SgrA*,   

    From Universe Today: “Amazing High Resolution Image of the Core of the Milky Way, a Region with Surprisingly Low Star Formation Compared to Other Galaxies” 

    universe-today

    Universe Today

    27 Feb , 2018
    Matt Williams

    1
    The centre of the Milky Way Galaxy seen through NASA’s Spitzer Space Telescope. http://www.spitzer.caltech.edu/images/1540-ssc2006-02a-A-Cauldron-of-Stars-at-the-Galaxy-s-Center

    NASA/Spitzer Infrared Telescope

    Compared to some other galaxies in our Universe, the Milky Way is a rather subtle character. In fact, there are galaxies that are a thousands times as luminous as the Milky Way, owing to the presence of warm gas in the galaxy’s Central Molecular Zone (CMZ). This gas is heated by massive bursts of star formation that surround the Supermassive Black Hole (SMBH) at the nucleus of the galaxy.

    The core of the Milky Way also has a SMBH (Sagittarius A*) and all the gas it needs to form new stars.

    SgrA* NASA/Chandra

    But for some reason, star formation in our galaxy’s CMZ is less than the average. To address this ongoing mystery, an international team of astronomers conducted a large and comprehensive study of the CMZ to search for answers as to why this might be.

    The study, titled Star formation in a high-pressure environment: an SMA view of the Galactic Centre dust ridge recently appeared in the Monthly Notices of the Royal Astronomical Society. The study was led by Daniel Walker of the Joint ALMA Observatory and the National Astronomical Observatory of Japan, and included members from multiple observatories, universities and research institutes.

    See the full article here .

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  • richardmitnick 12:59 pm on February 23, 2018 Permalink | Reply
    Tags: , , , , , SgrA*,   

    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 11:00 am on February 23, 2018 Permalink | Reply
    Tags: , , , , , , S0-2 Star is Single and Ready for Big Einstein Test, SgrA*,   

    From Keck: “Astronomers Discover S0-2 Star is Single and Ready for Big Einstein Test” 

    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft) above sea level, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland


    Keck Observatory

    February 21, 2018
    Mari-Ela Chock, Communications Officer
    (808) 554-0567
    mchock@keck.hawaii.edu

    1
    Credit: S. SAKAI/The Great Astronomer Andrea Ghez who spotted SgrA* by waching S0-2 Star /W. M. KECK OBSERVATORY/ UCLA GALACTIC CENTER GROUP
    The orbit of S0-2 (light blue) located near the Milky Way’s supermassive black hole will be used to test Einstein’s Theory of General Relativity and generate potentially new gravitational models.

    Andrea Ghez, UCLA

    No companion found for famous young bright star orbiting Milky Way’s supermassive black hole SgrA*.

    2
    Lead author Devin Chu of Hilo, Hawaii is an astronomy graduate student at UCLA. The Hilo High School and 2014 Dartmouth College alumnus conducts his research with the UCLA Galactic Center Group, which uses the W. M. Keck Observatory on Hawaii Island to obtain scientific data. “Growing up on Hawaii Island, it feels surreal doing important research with telescopes on my home island. I find it so rewarding to be able to return home to conduct observations,” Chu said. Credit: D. CHU

    3
    The UCLA Galactic Center Group takes a photo together during a visit to Keck Observatory, located atop Maunakea, Hawaii. Members of the group will return to the Observatory this spring to begin observations of S0-2 as the star travels towards its closest distance to the Galactic Center’s supermassive black hole. Credit: UCLA GALACTIC CENTER GROUP

    Astronomers have the “all-clear” for an exciting test of Einstein’s Theory of General Relativity, thanks to a new discovery about S0-2’s star status.

    Up until now, it was thought that S0-2 may be a binary, a system where two stars circle around each other. Having such a partner would have complicated the upcoming gravity test.

    But in a study published recently in The Astrophysical Journal, a team of astronomers led by a UCLA scientist from Hawaii has found that S0-2 does not have a significant other after all, or at least one that is massive enough to get in the way of critical measurements that astronomers need to test Einstein’s theory.

    The researchers made their discovery by obtaining spectroscopic measurements of S0-2 using W. M. Keck Observatory’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) and Laser Guide Star Adaptive Optics.

    Keck OSIRIS

    “This is the first study to investigate S0-2 as a spectroscopic binary,” said lead author Devin Chu of Hilo, an astronomy graduate student with UCLA’s Galactic Center Group. “It’s incredibly rewarding. This study gives us confidence that a S0-2 binary system will not significantly affect our ability to measure gravitational redshift.”

    Einstein’s Theory of General Relativity predicts that light coming from a strong gravitational field gets stretched out, or “redshifted.” Researchers expect to directly measure this phenomenon beginning in the spring as S0-2 makes its closest approach to the supermassive black hole at the center of our Milky Way galaxy.

    This will allow the Galactic Center Group to witness the star being pulled at maximum gravitational strength – a point where any deviation to Einstein’s theory is expected to be the greatest.

    “It will be the first measurement of its kind,” said co-author Tuan Do, deputy director of the Galactic Center Group. “Gravity is the least well-tested of the forces of nature. Einstein’s theory has passed all other tests with flying colors so far, so if there are deviations measured, it would certainly raise lots of questions about the nature of gravity!”

    “We have been waiting 16 years for this,” said Chu. “We are anxious to see how the star will behave under the black hole’s violent pull. Will S0-2 follow Einstein’s theory or will the star defy our current laws of physics? We will soon find out!”

    The study also sheds more light on the strange birth of S0-2 and its stellar neighbors in the S-Star Cluster. The fact that these stars exist so close to the supermassive black hole is unusual because they are so young; how they could’ve formed in such a hostile environment is a mystery.

    “Star formation at the Galactic Center is difficult because the brute strength of tidal forces from the black hole can tear gas clouds apart before they can collapse and form stars,” said Do.

    “S0-2 is a very special and puzzling star,” said Chu. “We don’t typically see young, hot stars like S0-2 form so close to a supermassive black hole. This means that S0-2 must have formed a different way.”

    There are several theories that provide a possible explanation, with S0-2 being a binary as one of them. “We were able to put an upper limit on the mass of a companion star for S0-2,” said Chu. This new constraint brings astronomers closer to understanding this unusual object.

    “Stars as massive as S0-2 almost always have a binary companion. We are lucky that having no companion makes the measurements of general relativistic effects easier, but it also deepens the mystery of this star,” said Do.

    The Galactic Center Group now plans to study other S-Stars orbiting the supermassive black hole, in hopes of differentiating between the varying theories that attempt to explain why S0-2 is single.

    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 2:44 pm on February 21, 2018 Permalink | Reply
    Tags: , , , , , IAC CanariCam on the Gran Telescopio Canarias at Roque de los Muchachos Observatory, MNRAS, SgrA*   

    From RAS: “Magnetic field traces gas and dust swirling around supermassive black hole” 

    Royal Astronomical Society

    Royal Astronomical Society

    21 February 2018

    Media contacts

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7292 3979
    Mob: +44 (0)7802 877699
    rmassey@ras.ac.uk

    Dr Helen Klus
    Royal Astronomical Society
    Tel: +44 (0)20 7292 3976
    hklus@ras.ac.uk

    Science contact

    Professor Pat Roche
    University of Oxford
    pat.roche@physics.ox.ac.uk

    Astronomers reveal a new high resolution map of the magnetic field lines in gas and dust swirling around the supermassive black hole at the centre of our Galaxy, published in a new paper in Monthly Notices of the Royal Astronomical Society.

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

    The team, led by Professor Pat Roche of the University of Oxford, created the map, which is the first of its kind, using the CanariCam infrared camera attached to the Gran Telescopio Canarias sited on the island of La Palma.

    IAC CanariCam on the Gran Telescopio Canarias at Roque de los Muchachos Observatory island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    Black holes are objects with gravitational fields so strong that not even light can escape their grasp. The centre of almost every galaxy appears to host a black hole, and the one we live in, the Milky Way, is no exception. Stars move around the black hole at speeds of up to 30 million kilometres an hour, indicating that it has a mass of more than a million times our Sun.

    2
    The colour scale in the image shows the amount of infrared (heat) radiation coming from warm dust particles in the filaments and luminous stars within a light year of the Galactic centre. The position of the black hole is indicated by an asterisk. The lines trace the magnetic field directions and reveal the complex interactions between the stars and the dusty filaments, and the impact that they and the gravitational force has on them. Credit: E. Lopez-Rodriguez / NASA Ames / University of Texas at San Antonio.

    Visible light from sources in the centre of the Milky Way is blocked by clouds of gas and dust. Infrared light, as well as X-rays and radio waves, passes through this obscuring material, so astronomers use this to see the region more clearly. CanariCam combines infrared imaging with a polarising device, which preferentially filters light with the particular characteristics associated with magnetic fields.

    The new infrared map covers a region about 1 light year on each side of the supermassive black hole. The map shows the intensity of infrared light, and traces magnetic field lines within filaments of warm dust grains and hot gas, which appear as thin lines reminiscent of brush strokes in a painting.

    The filaments, several light years long, appear to meet close to the black hole (at a point below centre in the map), and may indicate where orbits of streams of gas and dust converge. One prominent feature links some of the brightest stars in the centre of the Galaxy. Despite the strong winds flowing from these stars, the filaments remain in place, bound by the magnetic field within them. Elsewhere the magnetic field is less clearly aligned with the filaments. Depending on how the material flows, some of it may eventually be captured and engulfed by the black hole.

    The new observations give astronomers more detailed information on the relationship between the bright stars and the dusty filaments. The origin of the magnetic field in this region is not understood, but it is likely that a smaller magnetic field is stretched out as the filaments are elongated by the gravitational influence of the black hole and stars in the galactic centre.

    Roche praises the new technique and the result: “Big telescopes like GTC, and instruments like CanariCam, deliver real results. We’re now able to watch material race around a black hole 25,000 light years away, and for the first time see magnetic fields there in detail.”

    The team are using CanariCam to probe magnetic fields in dusty regions in our galaxy. They hope to obtain further observations of the Galactic Centre to investigate the larger scale magnetic field and how it links to the clouds of gas and dust orbiting the black hole further out at distances of several light years.

    Science paper:
    The Magnetic Field in the central parsec of the Galaxy

    See the full article here .

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  • richardmitnick 5:44 pm on February 17, 2018 Permalink | Reply
    Tags: , , , , , , , , SgrA*   

    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.

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    ALMA on the Chajnantor plateau at 5,000 metres.

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

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    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

     
  • richardmitnick 10:55 am on January 25, 2018 Permalink | Reply
    Tags: , , , , , , Forming Stars Near Our Supermassive Black Hole, Photoevaporative protoplanetary disks, SgrA*   

    From AAS NOVA: “Forming Stars Near Our Supermassive Black Hole” 

    AASNOVA

    AAS NOVA

    24 January 2018
    Susanna Kohler

    1
    Eleven bipolar outflows — signatures of star formation — have been discovered in the very center of our galaxy, near the supermassive black hole Sgr A*. [Yusef-Zadeh et al. 2017.]

    Is it possible to form stars in the immediate vicinity of the hostile supermassive black hole at the center of our galaxy? New evidence suggests that nature has found a way.

    2
    Infrared view of the central 300 light-years of our galaxy. [Hubble: NASA/ESA/Q.D. Wang; Spitzer: NASA/JPL/S. Stolovy]

    Too Hostile for Stellar Birth?

    Around Sgr A*, the supermassive black hole lurking at the Milky Way’s center, lies a population of ~200 massive, young, bright stars.

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

    Their very tight orbits around the black hole pose a mystery: did these intrepid stars somehow manage to form in situ, or did they instead migrate to their current locations from further out?

    For a star to be born out of a molecular cloud, the self-gravity of the cloud clump must be stronger than the other forces it’s subject to. Close to a supermassive black hole, the brutal tidal forces of the black hole dominate over all else. For this reason, it was thought that stars couldn’t form in the hostile environment near a supermassive black hole — until clues came along suggesting otherwise.

    Science as an Iterative Process

    3
    Very Large Array observations of candidate photoevaporative protoplanetary disks discovered in 2015. [Yusef-Zadeh et al. 2015]

    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)

    Longtime AAS Nova readers might recall that one of our very first highlights on the site, back in August of 2015, was of a study [The Astrophysical Journal Letters] led by Farhad Yusef-Zadeh of Northwestern University. In this study, the authors presented observations of candidate “proplyds” — photoevaporative protoplanetary disks suggestive of star formation — within a few light-years of the galactic center.

    While these observations seemed to indicate that stars might, even now, be actively forming near Sgr A*, they weren’t conclusive evidence. Follow-up observations of these and other signs of possible star formation were hindered by the challenges of observing the distant and crowded galactic center.

    Two and a half years later, Yusef-Zadeh and collaborators are back — now aided by high-resolution and high-sensitivity observations of the galactic center made with the Atacama Large Millimeter-Submillimeter Array (ALMA).

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

    And this time, they consider what they found to be conclusive.

    4
    ALMA observations of BP1, one of 11 bipolar outflows — signatures of star formation — discovered within the central few light-years of our galaxy. BP1 is shown in context at left and zoomed in at right; click for a closer look. [Yusef-Zadeh et al. 2017.]

    Unambiguous Signatures

    The authors’ deep ALMA observations of the galactic center revealed the presence of 11 bipolar outflows within a few light-years of Sgr A*. These outflows appear as approaching and receding lobes of dense gas that were likely swept up by the jets created as stars were formed within the last ~10,000 years. Yusef-Zadeh and collaborators argue that the bipolar outflows are “unambiguous signatures of young protostars.”

    Based on these sources, the authors calculate an approximate rate of star formation of ~5 x 10-4 solar masses per year in this region. This is large enough that such low-mass star formation over the past few billion years could be a significant contributor to the stellar mass budget in the galactic center.

    6
    Locations and orientations of the 11 bipolar outflows found. [Yusef-Zadeh et al. 2017]

    The question of how these stars were able to form so near the black hole remains open. Yusef-Zadeh and collaborators suggest the possibility of events that compress the host cloud, creating star-forming condensations with enough self-gravity to resist tidal disruption by Sgr A*’s strong gravitational forces.

    To verify this picture, the next step is to build a detailed census of low-mass star formation at the galactic center. We’re looking forward to seeing how this field has progressed by the next time we report on it!

    Citation

    F. Yusef-Zadeh et al 2017 ApJL 850 L30. http://iopscience.iop.org/article/10.3847/2041-8213/aa96a2/meta

    Related Journal Articles

    Signatures of Young Star Formation Activity within Two Parsecs of Sgr A* http://iopscience.iop.org/article/10.1088/0004-637X/808/1/97
    Sgr A* and Its Environment: Low-mass Star Formation, the Origin of X-Ray Gas and Collimated Outflow http://iopscience.iop.org/article/10.3847/0004-637X/819/1/60
    Tidal Distortion of the Envelope of an AGB Star IRS 3 near Sgr A* http://iopscience.iop.org/article/10.3847/1538-4357/aa5ea2/
    Radio Continuum Observations of the Galactic Center: Photoevaporative Proplyd-like Objects Near Sgr A* http://iopscience.iop.org/article/10.1088/2041-8205/801/2/L26/
    ALMA Observations of the Galactic Center: SiO Outflows and High-mass Star Formation near Sgr A* http://iopscience.iop.org/article/10.1088/2041-8205/767/2/L32/
    Abundant CH3OH Masers but no New Evidence for Star Formation in GCM0.253+0.016 http://iopscience.iop.org/article/10.1088/0004-637X/805/1/72/

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    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 7:01 am on January 11, 2018 Permalink | Reply
    Tags: , , , , , , SgrA*,   

    From Futurism: “This Year, We’ll See a Black Hole for the First Time in History” 

    futurism-bloc

    Futurism

    1.10.18
    Kristin Houser

    Using data collected from their network of telescopes, the Event Horizons Telescope team hopes to produce the first ever image of a black hole in 2018.

    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

    First Look At A Black Hole

    Within the next 12 months, astrophysicists believe they’ll be able to do something that’s never been done before, and it could have far-reaching implications for our understanding of the universe. A black hole is a point in space with a gravitational pull so strong that not even light can escape from it. Albert Einstein predicted the existence of black holes in his theory of general relativity, but even he wasn’t convinced that they actually existed. And thus far, no one has been able to produce concrete evidence that they do. The Event Horizon Telescope (EHT) could change that.

    The EHT isn’t so much one telescope as it is a network of telescopes around the globe. By working in harmony, these devices can provide all of the components necessary to capture an image of a black hole.

    “First, you need ultra-high magnification — the equivalent of being able to count the dimples on a golf ball in Los Angeles when you are sitting in New York,” EHT Director Sheperd Doeleman told Futurism.

    Next, said Doeleman, you need a way to see through the gas in the Milky Way and the hot gas surrounding the black hole itself. That requires a telescope as big as the Earth, which is where the EHT comes into play.

    The EHT team created a “virtual Earth-sized telescope,” said Doeleman, using a network of individual radio dishes scattered across the planet. They synchronized the dishes so that they could be programmed to observe the same point in space at the exact same time and record the radio waves they detected onto hard disks.

    The idea was that, by combining this data at a later date, the EHT team could produce an image comparable to one that could have been created using a single Earth-sized telescope.

    In April 2017, the EHT team put their telescope to the test for the first time. Over the course of five nights, eight dishes across the globe set their sights on Sagittarius A* (Sgr A*), a point in the center of the Milky Way that researchers believe is the location of a supermassive black hole.

    Data from the South Pole Telescope didn’t reach the MIT Haystack Observatory until mid-December due to a lack of cargo flights out of the region. Now that the team has the data from all eight radio dishes, they can begin their analysis in the hopes of producing the first image of a black hole.

    Proving Einstein Right (or Wrong)

    Not only would an image of a black hole prove that they do exist, it would also reveal brand new insights into our universe.

    “The impact of black holes on the universe is huge,” said Doeleman. “It’s now believed that the supermassive black holes at the center of galaxies and the galaxies they live in evolve together over cosmic times, so observing what happens near the event horizon will help us understand the universe on larger scales.”

    In the future, researchers could take images of a single black hole over time. This would allow the scientists to determine whether or not Einstein’s theory of general relativity holds true at the black hole boundary, as well as study how black holes grow and absorb matter, said Doeleman.

    See also https://bhi.fas.harvard.edu/ and http://eventhorizontelescope.org/

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Futurism covers the breakthrough technologies and scientific discoveries that will shape humanity’s future. Our mission is to empower our readers and drive the development of these transformative technologies towards maximizing human potential.

     
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