But this May, NASA revealed data from its Hubble Space telescope providing the best proof yet that black holes are indeed real.

The telescope measured the velocity of gases swirling closely around the center of M87, an elliptical galaxy in the Virgo cluster, about 50 million light-years away from Earth.

The gases were found to be spinning so quickly that only an unusually massive object at the galaxy's center could exert enough gravity to keep them in orbit.

According to the current theories of physics, only a black hole is sufficiently massive to exert such an attractive force.

"[The telescope's data] is very significant because it nails down in a very definite way something that had been widely believed," says professor of Astronomy and Physics William H. Press' 69 "I think now it's almost impossible to doubt the conclusion that it's a black hole."

But not all scientists agree about the finality of the Hubble finding, which reveals only the existence of a large mass in a small space.

"It could be a big bowling ball in there for all we know but we don't know of any bowling balls of a billion solar masses," says Professor of Astronomy Robert P. Kirshner '70.

Very Dense Objects

Black holes are really not holes at all, but rather dense objects with incredibly strong gravitational fields from which even light cannot escape.

While most dying stars evolve into planetsized white dwarfs stars with masses greater than three times that of the sun explode as supernovae and then crush themselves under their own gravity to become black holes.

No one supernova, however could have formed the black hole found by the Hubble telescope.

Because it has the mass of about 2 billion suns and spans the size of the solar system, Kirshner says the black hole is termed "supermassive."

Kirshner, who chairs the astronomy department, himself studies supernovae using the Hubble telescope most recently one in the Whirlpool galaxy.

Supermassive black holes may arise from a whole cluster of stars collapsing at the center, he say.

Professor of Astronomy Margaret J. Geller, who teaches Astronomy 14, "The Universe and Everything," says the black hole could have accumulated such a great mass by "gobling" up nearby objects for a few billion years.