We think we know what black holes look like. NASA renderings and sci-fi special effects artists usually imagine the eerie glowing ring of an event horizon around what appears to be an impenetrable dark chasm. It happens that they aren't so far off from the truth — and a groundbreaking (sky-breaking?) telescope is about to prove it.
Supermassive black holes have long been suspected to lurk at the center of every galaxy, including ours. These mysterious phenomena were initially predicted by Einstein's Theory of Gravity over a hundred years ago. Don't get any time-travel ideas yet, but their gravitational power is intense enough to warp space-time. Activity that occurs at the edge of one of these dark leviathans can actually ripple through the entire galaxy it resides in. Despite their awe-inspiring power that has fueled pages and pages of brilliant science fiction and even an iconic Muse song, no one has actually ever seen one.
Sagittarius A* is believed to be the supermassive black hole at the center of our galaxy. At four million solar masses and with an event horizon thought to measure 12.4 million miles across, SgrA* seems enormous even from 26,000 light years away, but its extreme gravity crushes and concentrates mass into a relatively small space. Astronomers have never been able to confirm its existence, having relied on its effects on surrounding space and celestial objects to give them a theoretical photo. Black holes are impossible to photograph because light cannot reflect that chasm of doom or escape from it. With no light to capture, there can be no image. There is, however, one source of light surrounding a black hole: its event horizon.
Scientists behind the Event Horizon Telescope (EHT) array are looking to change how we (literally) see the event horizons of black holes like SgrA*. Though EHT has been in development for two decades, it is finally on the brink of making black hole images a reality. Powered by numerous antennas from radio telescopes in several locations, it is able to see details 2,000 times tinier than even Hubble can.
Data from the 12 participating teams manning these telescopes will be collected the week of April 5, then recorded onto hard drives. Very long baseline array interferometry — which creates the illusion of one Earth-size radio telescope — will be used by a team of astronomers at MIT Haystack Observatory to piece that data together. Something visible should then start to emerge.
"In essence, we are making a virtual telescope with a mirror that is as big as the Earth," said Sheperd Doeleman, astronomer and principal investigator of the Event Horizon Telescope. "Each radio telescope we use can be thought of as a small silvered portion of a large mirror. With enough such silvered spots, one can start to make an image."
Now for the question of how this image will actually appear. Astronomers collaborating on the project believe the event horizon of SgrA* will look like a glowing ring around a black abyss, not too much unlike all those renderings and possibly stranger than science fiction. The Doppler effect (decrease in light frequency as an observer moves away from an object and vice-versa) will make it look more like a crescent from far, far away.....except that's no moon.
Expect to see photographic evidence of a supermassive black hole sometime next year.