United States and Canadian astronomers have found the second ''probable'' black hole so far discovered in the universe. This strengthens the case for considering these bizarre theoretical objects as more than science fiction.
Theoretically, when a massive star is dying, it can collapse so compactly its gravity becomes too strong even for light to escape. However, astronomers can't yet prove black holes actually exist.
The strongest case has been that of an unseen companion to a massive star in the constellation Cygnus. It is associated with the X-ray source Cygnus X-1.
Now there is a second black hole candidate. Anne P. Cowley of the University of Michigan and David Crampton and John B. Hutchings of the Dominion Astrophysical Observatory in Victoria, B.C., have located it outside our galaxy in the nearby Large Magellanic Cloud.
As described in a joint announcement of the US National Science Foundation and the Canadian National Research Council, the object, called LMC-X3 (Large Magellanic Cloud X-ray source 3), also is a powerful X-ray source. It, too, shows up as an (optically) unseen companion of a normal star.
The star and the presumed black hole orbit each other once in 41 hours. The star has about six times the mass of the sun, while the black hole has an estimated mass of 8 to 12 suns.
The astronomers made their findings at the Cerro Tololo Inter-American Observatory in Chile. These are consistent with a theory in which a black hole siphons gases from a companion star. The gases entering the black hole give off X-rays.
Some theorists invoke black holes to explain a variety of cosmic phenomena, including the energy source of galactic explosions. However, other astronomers have grown increasingly skeptical. ''It's comforting to know we've found that Cygnus X-1 is not the only black hole and we can presume there are many more,'' Dr. Cowley says.