![]() ![]() “Every morning, there’s a frenetic set of phone calls and analyses of weather data and telescope readiness, and then we make a go/no-go decision for the night’s observing,” says astronomer Geoffrey Bower of the Academia Sinica Institute of Astronomy and Astrophysics in Hilo, Hawaii. Researchers’ biggest enemy is water in the atmosphere, like rain or snow, which can muddle with the millimeter-wavelength radio waves that the EHT’s telescopes are tuned to.īut planning for weather on several continents can be a logistical headache. Schimpf (SMA) Daniel Luong-Van/NSF (SPT)ĮHT observing campaigns are best run within about 10 days in late March or early April, when the weather at every observatory promises to be the most cooperative. ![]() Tafreshi/ESO (APEX) Nicolas Billot/IRAM James Lowenthal/Smith College, UMass Amherst (LMT) David Harvey/Univ. Here’s where the observatories are located and how many dishes they contributed to the effort. Data from seven were used to create a picture of the black hole inside the galaxy M87 since M87 appears in the northern sky, the South Pole observatory couldn’t see it. Their mission: to image a supermassive black hole for the first time. These eight radio observatories teamed up in 2017 to work together as a global telescope, called the Event Horizon Telescope network. “Anything that you were just barely struggling to detect before, you get really solid detections now.” “ALMA changed everything,” says Vincent Fish, an astronomer at MIT’s Haystack Observatory in Westford, Mass. With a combined dish area larger than an American football field, ALMA collects far more radio waves than other observatories. Among the newcomers was the Atacama Large Millimeter/submillimeter Array, or ALMA, located on a high plateau in northern Chile. By 2017, there were eight observing stations in North America, Hawaii, Europe, South America and the South Pole. Over time, the EHT recruited new radio observatories. But the small telescope cohort didn’t yet have the magnifying power to reveal the black hole itself. In 2009, a network of just four observatories - in Arizona, California and Hawaii - got the first good look at the base of one of the plasma jets spewing from the center of M87’s black hole ( SN: 11/3/12, p. The EHT was not always the hotshot array that it is today, though. For the EHT in 2017, that was the distance from the South Pole to Spain. The diameter of that virtual dish is equal to the length of the longest distance, or baseline, between two telescopes in the network. Instead, a technique called very long baseline interferometry combines radio waves seen by many telescopes at once, so that the telescopes effectively work together like one giant dish. “The trick is that you don’t cover the entire Earth with an observatory.” ![]() All you need to know about the history of black holesĮven for radio astronomers, who are no strangers to building big dishes ( SN Online: 9/29/17), “this seems a little too ambitious,” says Loeb, who was not involved in the black hole imaging project.The first picture of a black hole opens a new era of astrophysics.The project of imaging M87’s black hole required observatories across the globe working in tandem as one virtual Earth-sized radio dish with sharper vision than any single observatory could achieve on its own. Black holes take up a minuscule sliver of sky and, from Earth, appear very faint. Though scientists have collected plenty of indirect evidence for black holes over the last half century, “seeing is believing.”Ĭreating that first-ever portrait of a black hole was tricky, though. “There is nothing better than having an image,” says Harvard University astrophysicist Avi Loeb. ![]() That’s what the Event Horizon Telescope, or EHT, did in April 2017, collecting data that has now yielded the first image of a supermassive black hole, the one inside the galaxy M87. Telescopes can look instead for the silhouette of a black hole’s event horizon - the perimeter inside which nothing can be seen or escape - against its accretion disk. Luckily, there’s a way to “see” a black hole without peering into the abyss itself. But because a black hole’s extreme gravity prevents light from escaping, the dark hearts of these cosmic heavy hitters remain entirely invisible. Up close, these behemoths are surrounded by glowing accretion disks of infalling material. Supermassive black holes, ensconced in the centers of galaxies, make themselves visible by spewing bright jets of charged particles or by flinging away or ripping up nearby stars. ![]()
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