Scientists are working on a pioneering scheme to view the massive black hole at the center of our galaxy.
The Event Horizon Telescope (EHT), hopes the team, will be able to image the ring of matter at the event horizon that surrounds the black hole.
"Even five years ago, such a proposal would not have seemed credible," says Sheperd Doeleman, assistant director of the Haystack Observatory at MIT and principal investigator of the EHT. "Now we have the technological means to take a stab at it."
Black holes can't themselves be seen, because no light can escape their fierce gravity - but the matter at the event horizon can.
"As dust and gas swirls around the black hole before it is drawn inside, a kind of cosmic traffic jam ensues," says Doeleman.
"Swirling around the black hole like water circling the drain in a bathtub, the matter compresses and the resulting friction turns it into plasma heated to a billion degrees or more, causing it to ‘glow’ – and radiate energy that we can detect here on Earth."
The EHT will consist of up to 50 radio telescopes scattered around the globe, including the Submillimeter Telescope on Mt. Graham in Arizona, telescopes on Mauna Kea in Hawaii and the Combined Array for Research in Millimeter-wave Astronomy in California.
The global array will include several radio telescopes in Europe, a 10-meter dish at the South Pole and potentially a 15-meter antenna atop a 15,000-foot peak in Mexico.
"In essence, we are making a virtual telescope with a mirror that is as big as the Earth," says Doeleman. "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."
Black holes remain poorly understood. Most if not all galaxies are now believed to harbor a supermassive black hole at their center, and smaller ones are scattered throughout. Our Milky Way is known to be home to about 25 smallish black holes ranging from five to 10 times the sun’s mass.
"What is great about the one in the center of the Milky Way is that is big enough and close enough," says Dan Marrone, an assistant professor of astronomy at Steward Observatory.
"There are bigger ones in other galaxies, and there are closer ones, but they’re smaller. Ours is just the right combination of size and distance."