From Physorg.com:
The field of gravity around a black hole is so immense that it swallows everything in its reach; not even light can escape its grip. For that reason, black holes are just that –emitting no light whatsoever, their “nothingness” blends into the black void of the universe.
So how does one take a picture of something that by definition is impossible to see?
“As dust and gas swirls around the black hole before it is drawn inside, a kind of cosmic traffic jam ensues,” Doeleman explained. “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.”
By imaging the glow of matter swirling around the black hole before it goes over the edge of the point of no return and plunges into the abyss of space and time, scientists can only see the outline of the black hole, also called its shadow. Because the laws of physics either don't apply to or cannot describe what happens beyond that point of no return from which not even light can escape, that boundary is called the Event Horizon.
“So far, we have indirect evidence that there is a black hole at the center of the Milky Way,” Psaltis said. “But once we see its shadow, there will be no doubt.”
Even though the black hole suspected to sit at the center of our galaxy is a supermassive one at four million times the mass of the Sun, it is tiny to the eyes of astronomers. Smaller than Mercury's orbit around the Sun, yet almost 26,000 light years away, it appears about the same size as a grapefruit on the moon.
“To see something that small and that far away, you need a very big telescope, and the biggest telescope you can make on Earth is to turn the whole planet into a telescope,” Marrone said.
To that end, the team is connecting up to 50 radio telescopes scattered around the globe…
More here.