The face of a Black Hole
Scientists have unmasked mystery incarnate. On April 10, representatives of the Event Horizon Telescope collaboration unveiled a reconstructed image of the gargantuan black hole that squats in the heart of the giant elliptical galaxy M87. The black hole is an invisible behemoth, so large that light would take 1½ days to cross it.
And it’s beautiful.
“We have seen what we thought was unseeable,” said EHT director Sheperd Doeleman (Center for Astrophysics, Harvard & Smithsonian) during a National Science Foundation press conference in Washington, DC. “We have seen and taken a picture of a black hole. Here it is.”
An outcome of Einstein’s equations of gravity, black holes have suffered a century of disbelief, debate and then wonder as scientists grappled with their existence. It was astronomical observations of blazing beacons in distant galaxies, as well as of invisible partners to stars closer to home, that ultimately turned the tide in black holes’ favour in the late 20th century. They are now thought to exist at a wide range of masses, from the corpses of individual stars to colossi that serve as key players in galaxies’ evolution. We’ve even detected ripples in spacetime created by objects that behave just as colliding black holes should.
But until the EHT, no one had ever seen one. “Science fiction has become science fact,” says theorist Avery Broderick (Perimeter Institute and University of Waterloo, Canada).
The shadow knows
Technically speaking, the EHT’s radio images don’t show the black hole but rather the silhouette of its defining characteristic — the , the point of no return. As gas, explains EHT astronomer Feryal Özel (University of Arizona). But if the light continues inward, it will plunge past the event horizon and never reach us. These effects combine to create what’s called the black hole’s : a dark circle surrounded by a bright halo. The halo’s inner edge is the photon ring.
