ATLANTA -- Astronomers believe that they are a measurement away from definitive proof of the existence of black holes, those central regions of some galaxies where matter would be so dense and the pull of gravity so strong that nothing, not even light, could escape from them.
Einstein's theory predicted black holes, and current astrophysical theory assumes that they exist, but the hunt for proof of their existence has been going on for two decades without clear success.
New observations reported here yesterday at a meeting of the American Astronomical Society were seen as the strongest evidence so far of a black hole of extreme mass residing at the center of a galaxy, sucking in a whirlpool of surrounding stars.
A team of astronomers led by Dr. Tod R. Lauer of the National Optical Astronomy Observatories in Tucson, Ariz., said images taken by the Hubble Space Telescope showed an unusual concentration of stars at the center of galaxy M87. They appeared to be drawn there by the gravity of a black hole whose mass was estimated to be 2.6 billion times that of the sun.
Scientists said this finding and other characteristics of the galaxy made them 90 percent certain that they were observing the effects of an extraordinarily massive black hole.
Calling the results "very, very important," Dr. James E. Hesser, director of the Dominion Astrophysical Observatory in Victoria, British Columbia, said that the images were "making more and more credible the concept of black holes."
Dr. Lauer emphasized that the images of especially dense starlight alone did not prove conclusively the black hole's presence. "It looks like a duck, but we haven't heard it quack yet," he said at a news conference.
The "quack" may be forthcoming, scientists said. Spectroscopic observations by the orbiting Hubble telescope in the next few months will measure the velocity of the stars orbiting within the galactic nucleus. High velocities should be conclusive evidence of a black hole and would provide astronomers with a direct measurement of its mass.
Officials of the Space Telescope Science Institute in Baltimore said they were concerned that the Hubble's flawed mirror might preclude the detailed observations required for such confirmation. Plans to install corrective optics in the telescope, however, could yield the required velocity measurements within three years.
"Then the black hole should be undeniable," Dr. Lauer said.
Dr. Holland Ford, an astronomer at the space telescope institute, said: "In the minds of astronomers, there's no doubt that black holes do exist. What we really want to know is their mass."
Discovering the existence of black holes was one of the primary objectives of the Hubble telescope, which was launched into an Earth orbit in April 1990.