![]() 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. These measurements provide the first opportunity to image horizon-scale structure in M87.Black holes are extremely camera shy. The M87 data reveal the presence of two nulls in correlated flux density at ~3.4 and ~8.3 giga-lambda and temporal evolution in closure quantities, indicating intrinsic variability of compact structure on a timescale of days, or several light-crossing times for a few billion solar-mass black hole. They are validated through a series of quality assurance tests that show consistency across pipelines and set limits on baseline systematic errors of 2% in amplitude and 1 degree in phase. The final data products include calibrated total intensity amplitude and phase information. In response, we developed three independent pipelines for phase calibration and fringe detection, each tailored to the specific needs of the EHT. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA) reaching an angular resolution of 25 micro-as, with characteristic sensitivity limits of ~1 mJy on baselines to ALMA and ~10 mJy on other baselines. Data Processing and Calibration, by The Event Horizon Telescope Collaboration Download PDF Abstract:We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5-11 observing campaign. Download a PDF of the paper titled First M87 Event Horizon Telescope Results.
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