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

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

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

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

    U Arizona bloc

    University of Arizona

    Feb. 21, 2018
    Daniel Stolte

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

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

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

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

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

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

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

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

    Study Relies on Simulations

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

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

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

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

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

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

    Event Horizon Telescope Array

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

    ESO/APEX
    Atacama Pathfinder EXperiment

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

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

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

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

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

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

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

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    NSF CfA Greenland telescope

    Greenland Telescope

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

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

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

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

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

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

    Applications Could Be Extensive

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

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

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

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

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

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

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

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

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

    See the full article here .

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

     
  • richardmitnick 1:39 pm on January 24, 2018 Permalink | Reply
    Tags: , , , , , EHT - Event Horizon Telescope   

    From astrobites: “Hunting for new physics in a black hole’s shadow” 

    Astrobites bloc

    astrobites

    Jan 24, 2018
    Aaron Tohuvavohu

    Title: Event Horizon Telescope Observations as Probes for Quantum Structure of Astrophysical Black Holes
    Authors: Steven B. Giddings & Dimitrios Psaltis
    First Author’s Institution: University of California, Santa Barbara

    Status: Submitted to Phys Rev D, open access on the arXiv.

    For 5 days in April of 2017, 8 radio telescopes on 4 continents all pointed in concert at Sagittarius A*, the supermassive black hole at the center of our galaxy.

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

    During this observing campaign these 8 telescopes effectively became one Earth-sized radio telescope, the Event Horizon Telescope (EHT).

    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

    Using hydrogen maser atomic clocks to track the difference in the arrival times of the radio signal at the various telescopes, the far-flung array can emulate a single telescope with an effective diameter equal to that of our planet, a technique called very long baseline interferometry (VLBI).

    See the full article here .

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    What do we do?

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

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

     
  • richardmitnick 7:01 am on January 11, 2018 Permalink | Reply
    Tags: , , , , EHT - Event Horizon Telescope, , ,   

    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 .

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    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.

     
  • richardmitnick 1:57 pm on January 3, 2018 Permalink | Reply
    Tags: , EHT - Event Horizon Telescope, ,   

    From Ethan Siegel: “2018 Will Be The Year Humanity Directly ‘Sees’ Our First Black Hole” 

    Ethan Siegel
    Jan 3, 2018

    1
    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.

    The Event Horizon Telescope has come online and taken its data. Now, we wait for the results.

    Black holes are some of the most incredible objects in the Universe. There are places where so much mass has gathered in such a tiny volume that the individual matter particles cannot remain as they normally are, and instead collapse down to a singularity. Surrounding this singularity is a sphere-like region known as the event horizon, from inside which nothing can escape, even if it moves at the Universe’s maximum speed: the speed of light. While we know three separate ways to form black holes, and have discovered evidence for thousands of them, we’ve never imaged one directly. Despite all that we’ve discovered, we’ve never seen a black hole’s event horizon, or even confirmed that they truly had one. Next year, that’s all about to change, as the first results from the Event Horizon Telescope will be revealed, answering one of the longest-standing questions in astrophysics.

    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

    The idea of a black hole is nothing new, as scientists have realized for centuries that as you gather more mass into a given volume, you have to move at faster and faster speeds to escape from the gravitational well that it creates. Since there’s a maximum speed that any signal can travel at — the speed of light — you’ll reach a point where anything from inside that region is trapped. The matter inside will try to support itself against gravitational collapse, but any force-carrying particles it attempts to emit get bent towards the central singularity; there is no way to exert an outward push. As a result, a singularity is inevitable, surrounded by an event horizon. Anything that falls into the event horizon? Also trapped; from inside the event horizon, all paths lead towards the central singularity.

    2
    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.

    Practically, there are three mechanisms that we know of for creating real, astrophysical black holes.

    1.When a massive enough star burns through its fuel and goes supernova, the central core can implode, converting a substantial fragment of the pre-supernova star into a black hole.
    2.When two neutron stars merge, if their combined post-merger mass is more than about 2.5-to-2.75 solar masses, it will result in the production of a black hole.
    3.And if either a massive star or a cloud of gas can undergo direct collapse, it, too, will produce a black hole, where 100% of the initial mass goes into the final black hole.

    3
    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.

    Over time, black holes can continue to devour matter, growing in both mass and size commensurately. If you double the mass of your black hole, its radius doubles as well. If you increase it tenfold, the radius goes up by a factor of ten, also. This means that as you go up in mass — as your black hole grows — its event horizon gets larger and larger. Since nothing can escape from it, the event horizon should appear as a black “hole” in space, blocking the light from all objects behind it, compounded by the gravitational bending of light due to the predictions of General Relativity. All told, we expect the event horizon to appear, from our point of view, 250% as large as the mass predictions would imply.

    4
    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, Universität Hildesheim; Axel Mellinger (background).

    Taking all of this into account, we can look at all the known black holes, including their masses and how far away they are, and compute which one should appear the largest from Earth. The winner? Sagittarius A*, the black hole at the center of our galaxy. Its combined properties of being “only” 27,000 light years distant while still reaching a spectacularly large mass that’s 4,000,000 times that of the Sun makes it #1. Interestingly, the black hole that hits #2 is the central black hole of M87: the largest galaxy in the Virgo cluster. Although it’s over 6 billion solar masses, it lies some 50–60 million light years away. If you want to see an event horizon, our own galactic center is the place to look.

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

    5
    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

    If you had a telescope the size of Earth, and nothing in between us and the black hole to block the light, you’d be able to see it, no problem. Some wavelengths are relatively transparent to the intervening galactic matter, so if you look at long-wavelength light, like radio waves, you could potentially see the event horizon itself. Now, we don’t have a telescope the size of Earth, but we do have an array of radio telescopes all across the globe, and the techniques of combining this data to produce a single image. The Event Horizon Telescope brings the best of our current technology together, and should enable us to see our very first black hole.

    Instead of a single telescope, 15-to-20 radio telescopes are arrayed across the globe, observing the same target simultaneously. With up to 12,000 kilometers separating the most distant telescopes, objects as small as 15 microarcseconds (μas) can be resolved: the size of a fly on the Moon. Given the mass and distance of Sagittarius A*, we expect that to appear more than twice as large as that figure: 37 μas. At radio frequencies, we should see lots of charged particles accelerated by the black hole, but there should be a “void” where the event horizon itself lies. If we can combine the data correctly, we should be able to construct a picture of a black hole for the very first time.

    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. Note the clear signature of the event horizon in all the expected results. Image credit: GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799.

    The telescopes comprising the Event Horizon Telescope took their very first shot at observing Sagittarius A* simultaneously last year. The data has been brought together, and it’s presently being prepared and analyzed. If everything operates as designed, we’ll have our first image in 2018. Will it appear as General Relativity predicts? There are some incredible things to test:

    -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.

    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).

    Whatever we do (or don’t) wind up discovering, we’re poised to make an incredible breakthrough simply by constructing our first-ever image of a black hole. No longer will we need to rely on simulations or artist’s conceptions; we’ll have our very first actual, data-based picture to work with. If it’s successful, it paves the way for even longer baseline studies; with an array of radio telescopes in space, we could extend our reach from a single black hole to many hundreds of them. If 2016 was the year of the gravitational wave and 2017 was the year of the neutron star merger, then 2018 is set up to be the year of the event horizon. For any fan of astrophysics, black holes, and General Relativity, we’re living in the golden age. What was once deemed “untestable” has suddenly become real.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 11:42 am on January 3, 2018 Permalink | Reply
    Tags: Celebrating Innovation, Celebrating Women in Physics, Continue the Journey, EHT - Event Horizon Telescope, , , Recent Perimeter News, The Centre for the Universe   

    From PI: “Recent Perimeter News” 

    Perimeter Institute

    Perimeter Institute

    A Stellar Year

    From the dawn of multi-messenger astronomy to the discovery of more Earth-sized exoplanets and a solar eclipse that captivated millions, 2017 was a year in which humanity turned its gaze skyward.

    Many believe we have entered a new “golden age” of physics. Researchers at Perimeter continue to probe for answers about dark matter, quantum gravity, black holes, and the birth of the universe.

    The Centre for the Universe

    In November 2017, Perimeter announced the creation of the Centre for the Universe – a new hub for cutting-edge cosmology research. Centre patrons include world-renowned cosmologist Stephen Hawking and Nobel Prize winner Art MacDonald. The Centre will bring together international scientists, bridging fundamental theory and experiment, to tackle questions about the origin, evolution, and fate of the universe.

    Read more here.

    On the Horizon

    The Event Horizon Telescope (EHT) project turned its incredibly precise gaze toward a black hole earlier this year, and the scientific world awaits the resulting imagery.

    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

    A process called Very Long Baseline Interferometry (VLBI) is used by this network of eight large radio telescopes to capture history’s first picture of a black hole’s event horizon. Avery Broderick leads Perimeter’s Event Horizon Initiative, which will help analyze and interpret the data collected by the telescope array. The EHT team is waiting for the last remaining data to arrive from the South Pole and expects to have results early in the new year.

    Read more here

    A Year of Celebration

    Celebrating Innovation

    Innovation150 – a part of Canada 150 celebrations – was led by Perimeter, with the Power of Ideas Tour visiting cities and towns across the country. More than 100,000 people attended tour events and many more attended talks, festivals, and other Innovation150 experiences.

    Read more here

    Celebrating Women in Physics

    Perimeter’s Emmy Noether Initiatives continued to celebrate and support women scientists throughout the year. A free, downloadable poster series also shone the spotlight on some women pioneers in physics.

    Read more here.

    Continue the Journey

    Advances in creating quantum light, determining what dark matter isn’t, sharing the wonders of science – Perimeter was a bustling hub of research, education, and outreach in 2017. Read more at http://www.insidetheperimeter.ca.

    Thank you for joining us on this journey. We look forward to sharing more exciting news with you throughout 2018.

    With appreciation,

    10

    Jacqueline Watty
    Senior Advancement Officer
    Perimeter Institute for Theoretical Physics
    519-569-7600 ext. 4472

    See the full article here .

    Please help promote STEM in your local schools.

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    About Perimeter

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

     
  • richardmitnick 2:58 pm on October 5, 2017 Permalink | Reply
    Tags: , An Update on the Event Horizon Telescope, EHT - Event Horizon Telescope   

    From AAAS: “An Update on the Event Horizon Telescope” 

    AAAS

    AAAS

    October 5, 2017
    Sheperd Doeleman
    Harvard-Smithsonian CfA

    The Event Horizon Telescope (EHT) is an international collaboration aiming to capture the first image of a black hole by creating a virtual Earth-sized radio telescope. We recently launched a new website that contains background material, the latest news from our team, and educational resources.

    At present, the EHT team is processing observations from a week-long observing campaign in April 2017 that linked together eight telescopes in Hawaii, Arizona, Spain, Mexico, Chile, and the South Pole via the technique of very-long-baseline interferometry (VLBI). This global array targeted two supermassive black holes, one at the center of the Milky Way and the other in M87, a giant elliptical galaxy about 50 million light-years away in Virgo. For each of these, the EHT has the magnifying power and sensitivity to form images of the millimeter-wavelength light emitted by hot gas near the event horizon. Einstein’s general theory of relativity predicts that the EHT should see a silhouette formed by the intense gravity of the black hole warping the light from infalling hot gas. The dynamics of matter may also be detected as hot blobs of material orbit the black hole and shear into turbulent flows.

    1
    The South Pole Telescope illuminated by aurora australis and the Milky Way. Jupiter is brightly visible at lower left. The outside temperature is -60°C. [Daniel Michalik / South Pole Telescope]

    Most data recorded at all the sites have been shipped to two central processing facilities, one at MIT Haystack Observatory and another at the Max Planck Institute for Radio Astronomy, where the signals are combined in VLBI correlators. We are still waiting for the hard disks containing data from the South Pole, where they have been stored during the long polar winter when there are no flights to/from the Amundsen-Scott station. Some data, however, were sent back from the South Pole via satellite, so we have confirmed that all the sites in the EHT worked well, and analysis of the data is getting started.

    On the technical side, the EHT has broken new ground by making VLBI observations at the shortest wavelengths to date. And the array has been extended to bandwidths, or data capture rates, that are more than 10 times what was possible just a few years ago. Parallel advances in theory are providing direction for analysis techniques through detailed modeling and simulations of black hole accretion. For more information on current EHT work in both of these areas, as well as updates, we encourage you to visit the project website.

    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

    See the full article here .

    The American Association for the Advancement of Science is an international non-profit organization dedicated to advancing science for the benefit of all people.

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

     
  • richardmitnick 11:14 am on August 23, 2017 Permalink | Reply
    Tags: , , , , , EHT - Event Horizon Telescope, ,   

    From astrobites: “Students on the Hunt for Black Holes” 

    Astrobites bloc

    Astrobites

    Aug 22, 2017
    Ana Torres Campos
    Crossposts, Personal Experiences

    Inside the Large Millimeter Telescope Alfonso Serrano (LMT), at an altitude of 4500 meters above sea level, Queen’s Don’t Stop Me Now can be heard in the background while a group of people cheer and shake hands after successfully concluding an observation run for one of the most important astronomical projects in the last years: The Event Horizon Telescope (EHT).

    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

    This project aims to obtain, for the first time ever, the image of the projected shadow of the supermassive black hole at the center of our galaxy, as well as the one in Messier 87.

    SGR A* NASA’s Chandra X-Ray Observatory

    1
    Messier 87, sources of images posted in graphic.

    In this post I share my personal experience as a guest of the team responsible for the observations of the EHT that were taken with the LMT in April of this year.

    2
    Figure 1 The LMT control room onApril 11th, 2017 at the end of the EHT 2017 observing run. Left to right: Antonio Hernández, Sergio Dzib, Emir Moreno, Edgar Castillo, Gopal Narayanan, Katie Bouman and Sandra Bustamante. Credit: Ana Torres Campos.

    Why should you care about the Event Horizon Telescope?
    The New York Times and National Geographic, among others, have written articles about the EHT, so don’t be surprised if one of these days your relatives or friends ask you about the project. Its greatness lies in not only being the first opportunity to observe an unknown event, or proving Einstein’s general relativity at never- imagined scales, but in demonstrating that, in times of discord, a close collaboration among a large number of nations is essential for scientific advancement.

    The Event Horizon Telescope is a network of eight [with ALMA it is now nine] millimeter-wave radio observatories located on four continents and representing over 20 nations. These observatories work together as a single Earth-sized telescope using the Very Large Baseline Interferometry (VLBI) technique. One of these facilities is the LMT, a 32-meter single-dish millimeter-wavelength telescope led by the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE, Mexico) and the University of Massachusetts Amherst (UMass, U.S.A.). Each night, the LMT synchronized (with a precision higher than 10-12 seconds) with the other telescopes using a hydrogen maser and recorded approximately 30 Terabytes of data which were stored in Mark 6 data systems developed by the Massachusetts Institute of Technology (MIT) Haystack Observatory.

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    Massachusetts Institute of Technology (MIT) Haystack Observatory.

    The observing run at the LMT

    The observing run was set to begin on April 4 with a 10-day window to accomplish five observing sessions. Some of the EHT team members got to the telescope site days before to check on the instruments (a 1.3-mm receiver, the backend system and the hydrogen maser) and get acclimated to the high altitude and time change (since the observations were to be performed at night time). My adventure began on May 31 when I met the EHT-LMT observing team, led by Dr. Gopal Narayanan (UMass researcher and the developer of the 1.3-mm receiver). I was really surprised that the crew consisted mainly of PhD students; Sandy, Aleks, and Michael are in their first years and Katie is a Computer Science PhD candidate. The first thing that came to mind was: how come young students are in charge of such an important task?! I got the answer to my question after spending a few days with them. Not only they are outstandingly capable but also they know how to work as a team.

    Since the observing sessions were to be ~17 hours long, the team split into two groups: Group 1 (David, Lindy, Aleks and Michael) began the observing session at 5:30 pm and ended at 2 am, and Group 2 (Edgar,Gopal, Katie and Sandy) started to observe at 1 am and finished at 10 am. This schedule allowed all of the team members to sleep for at least 6 hours, join with the Command Center (and the other observatories) at the 2:30 pm video conference for the go/no-go decision (given the weather conditions at the different sites), and having a one hour overlap in between observing groups’ shifts.

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    (Top) Left to Right: the 1.3-mm receiver, Sandra Bustamante, Aleksandar Popstefanija and Gopal Narayanan. (Bottom-Left) Sergio Dzib, Antonio Hernández and Gopal Narayanan, at the back stands the backend system with the Mark 6. (Bottom-Right) Gopal Narayanan checking the hydrogen maser.

    Both groups had an expert telescope operator (Edgar or David), but in one group was the backend system expert (Lindy) while in the other was the receiver expert (Gopal). This made the students a little nervous at first because if any problem arose then they would have had to face it alone before calling the expert (whom would very likely be sleeping at Base Camp).

    The first target of the observing run was a binary black hole called OJ 287.

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    http://www.as.up.krakow.pl/sz/oj287.html

    This object is scientifically interesting all on its own, but because it is a deeply studied object, it will instead be used to calibrate the observations of the project’s primary observing targets. These are Sagittarius A* (Sgt A*), the supermassive black hole at the center of our galaxy, and the supermassive black hole in M87, the most important object of the first night since Sgt A* observations were planned for the following days.

    This object is scientifically interesting all on its own, but because it is a deeply studied object, it will instead be used to calibrate the observations of the project’s primary observing targets. These are Sagittarius A* (Sgr A*), the supermassive black hole at the center of our galaxy, and the supermassive black hole in Messier 87, the most important object of the first night since Sgr A* observations were planned for the following days.

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    (Left) Members of the EHT project infront of the LMT. From left to right: Aleksandar Popstefanija, Michael Janssen, Sandra Bustamante, Lindy Blackburn, Katie Bouman, Gopal Narayanan and Edgar Castillo. (Middle) Lindy explains the data recording instructions to the students. (Right) Telescope operators David Sánchez and Edgar Castillo. Credit: Ana Torres Campos.

    Along with the observations came the uncomfortable situations that nobody talks about but that every observational astronomer has suffered from: power failure, difficulty to perfectly focus the telescope, and coffee shortage, the last one being the most stressful of them all. The good thing was that the exceptional skills of the telescope staff (including the operators) managed to quickly fix these inconveniences and halfway through the observing run reinforcement arrived: Antonio (a PhD student at IRyA/Université Toulouse III – Paul Sabatier) and Sergio (a postdoc at MPIFRA). Nevertheless, tiredness increased every day, but the 24-hour interactions among the team members helped them feel relaxed, increasing the moments of laughter and jokes.

    In my personal opinion, one of the keys to the EHT success is the excellent communication between the project team members, based not only on frequent videoconferences, emails and chats on Slack, but also a very well organized web or “wiki” where you can find the manuals of the instruments, tutorials on the observing run procedures, and even contact telephone numbers.

    What I learned from the EHT-LMT team
    1. An observing run will only be successful if the team works efficiently.
    2. It is necessary to be capable of occupying different roles on a team.
    3. Being assertive when listening and giving instructions will save you time.
    4. Relaxing and fun moments will improve the job performance of the team.
    Finally, I would like to thank Gopal, Katie, Michael, Sandy, Lindy, Aleks, David, Edgar, Antonio, Michael and Sergio for sharing with me such an incredible experience and to the LMT site and Base Camp crew for the outstanding job they do.

    See the full article here .

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

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
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  • richardmitnick 1:56 pm on August 15, 2017 Permalink | Reply
    Tags: Black hole imaging, EHT - Event Horizon Telescope, , ,   

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

    ESO 50 Large

    European Southern Observatory

    1.8.2017 Challenges in Obtaining an Image of a Supermassive Black Hole

    “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
    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

    Global mm-VLBI Array

    To make it possible to image the shadow of the event horizon of Sagittarius A*, 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. 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.

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    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.

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    A simulated image of the supermassive black hole Sagittarius A*, which is likely to be obtained in the most recent EHT observations. The dark gap at the centre is the shadow of the black hole. Credit: Kazunori Akiyama (MIT Haystack Observatory).

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

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

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

    See the full article here .

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

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

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

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

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

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

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

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

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

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

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

     
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