'It was one of the smoothest parts of the project,' says team member Feryal Г–zel of the University of Arizona in Tucson. Millimeter waves are affected by clouds, so getting good weather was important. The collaboration had made earlier observations with fewer telescopes, but 2017 was the first time they had a globe-spanning array that included the power of the Atacama Large Millimeter/submillimeter Array in Chile with its 64 dishes. 'Then the Earth turns so we can fill in the image.'

'You can think of them as silvered spots on a global mirror,' says Shep Doeleman, the EHT's project leader at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. The telescopes they used stretched from Hawaii to Arizona, Mexico to Spain, and Chile to the South Pole. So, the EHT team coopted most of the millimeter-wave telescopes worldwide and combined their data to produce a virtual telescope the size of Earth through a process called very-long-baseline interferometry. No existing telescope has the resolution to see such a distant, tiny object. Yet its event horizon is only 40 billion kilometers across-about four times the diameter of Neptune's orbit. The black hole at the center of M87, 55 million light-years away, has swallowed the mass of 6.5 billion suns. Black holes pack an immense amount of mass into a surprisingly small space. At that specific radio frequency, radiation can penetrate the haze of dust and gas that surrounds the centers of galaxies.Д«ut zooming in on the black holes was still a challenge. The EHT team, from 13 institutions around the world, made its observations of M87* and the black hole at the center of our Milky Way, known as Sagittarius A* (Sgr A*), over 5 nights in April 2017 using eight radio telescopes that are sensitive to wavelengths of about a millimeter. The observed shadow is essentially circular, Broderick says.Дata from the South Pole Telescope, one of the radio dishes used in the Event Horizon Telescope, overwintered in Antarctica before being combined with other data. General relativity predicts that the shadow ought to be round to within 10%, says Avery Broderick, an EHT member and astrophysicist at the University of Waterloo in Canada, whereas alternative theories of gravity predict distorted, noncircular shapes. The black hole bends light around it, creating a circular shadow. In the team's images, the bottom of the ring appears bright because the gases there are being Doppler-boosted, whipped toward Earth. As they consume matter that strays too close, they squeeze it into a superheated disk of glowing gas. Black holes have gravitational fields so strong that even light cannot escape, so they are defined by the shell of a black, featureless sphere called an event horizon. 'This is the end of space and time.' Falcke says the 2-year process of crunching the data and generating the images 'was the most emotionally difficult period of my life.'ДЄlthough few doubted the existence of black holes, seeing them-or at least their shadow-was an immense challenge. 'It feels like looking at the gates of hell,' says Heino Falcke of Radboud University in Nijmegen, the Netherlands, one of the leaders of the Event Horizon Telescope (EHT) collaboration, which announced the result in a global set of coordinated press conferences. It is also a feat for the team of more than 200 scientists who toiled for years to produce the image by combining signals from eight separate radio observatories spanning the globe. The result-a ring of fire surrounding the blackest of shadows-is a powerful confirmation of Albert Einstein's theory of gravity, or general relativity, which was used to predict black holes 80 years ago. Astronomers today revealed a picture of the gargantuan black hole at the heart of the nearby galaxy Messier 87 (M87). At last, we can see it: a black hole in the flesh.

Black hole event horizon