Hubble Heritage Team / ESA / NASA
Astronomers using NASA's Hubble Space Telescope received a boost from a cosmic magnifying glass to construct one of the sharpest maps of dark matter in the universe. They used Hubble's Advanced Camera for Surveys to chart the invisible matter in the massive galaxy cluster Abell 1689, located 2.2 billion light-years away.

Black holes are perhaps the most powerful, least understood phenomenon in the universe, but no one has ever really seen one. Astronomers are hoping to photograph one for the first time by linking 50 radio telescopes around the world so that Earth becomes essentially a single giant radio telescope.

The project is called the Event Horizon Telescope, and it will be aimed at a black hole in our own Milky Way galaxy. This black hole is of "supermassive" size, 4 million times the mass of the sun. It is so far away — almost 26,000 light-years — that if it could be seen, astronomers say it would be about the size of a grapefruit on the moon.

Black holes, created when giant stars collapse in on themselves, have a gravity so dense that nothing caught up in them — light, energy, matter — escapes. Thus, astronomers won't see the actual black hole, but conclusive evidence of its presence — the dust and gas circling around the hole, like water circling the drain in a bathtub, explained one.

As the matter circles and becomes ever more compressed, it will be heated to a billion degrees or more, creating a "glow" outlining the black hole that can be detected from Earth.

Einstein first postulated the existence of black holes in 1916 as part of his general theory of relativity. Subsequent observations have indicated that he was right, but the Event Horizon experiment will test one element of his theory.

In theory, the ring of swirling debris should form a perfect circle just before it disappears into the black hole. If it doesn't, that means a serious flaw in the theory and there's likely a Nobel Prize awaiting the scientist who figures out what it is. A larger examination of the black hole is slated for 2014, when 66 radio telescopes will be focused on it. But the mystery may only deepen.

At the center of a black hole, there is believed to be a "singularity," a point of zero volume and infinite density where time stands still. Our universe is thought to have begun as a singularity that blew up with such force, the "big bang," that the universe is still expanding 13.75 billion years later.

As the scientists are careful to point out, there is much we don't know. But a photo of a black hole, or at least of its outline, is a place to start.