stronomers have discovered a black hole that they think may give them a clear and revealing view of something never before observed: the climactic plunge of matter as it disappears into one of these cosmic gravitational sinks.
The effects of the black hole were first observed last year by two teams of astronomers working independently at the same telescope in Arizona. An outburst of X-rays from the region, recorded by a spacecraft, attracted their attention. It appears that the black hole has a normal star, smaller than the Sun, as an orbital companion and was beginning to take huge gravitational gulps of gas from the companion as it drew closer.
The acceleration and turbulence of the cannibalized matter generated the bursts of X-rays and also a pronounced brightening of visible light, a phenomenon called a nova. The energy was coming from the transfer of gas from the companion star into a disk of matter surrounding the invisible mass known as a black hole.
Astronomers said the black hole in question, a compact remnant of an exploded giant star, had a mass equivalent to 6 to 10 suns, making it a heavyweight among the few such stellar-class black holes. But it is nothing like the humongous ones, with millions of times the Sun's mass, lurking at the cores of most galaxies.
In a report prepared for publication soon in The Astrophysical Journal, astronomers said the newly observed object's relative proximity to Earth and the absence of obscuring dust clouds between here and there "make this system central to the study" of stellar-class black holes.
The object, about 5,000 light-years away, is situated above the plane inhabited by most of the stars and dusty interstellar matter in the Milky Way galaxy.
The lead author of the report is Dr. Jeffrey E. McClintock of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Another team, led by Dr. Craig Foltz, director of the MMT telescope at the Whipple Observatory near Tucson, produced similar findings.
Most of the observations were conducted at the MMT telescope, with some of the light measurements made by the Vatican Advanced Technology Telescope on Mount Graham in Arizona.
Dr. Foltz said the black hole observation was "the first splashy discovery" since the MMT telescope was completely renovated and enlarged.
Although 10 other similar systems of a black hole paired with a normal star have already been reported, Dr. Foltz said they were "still rare enough that each new one is important because there are still scientists who feel the whole idea of stellar black holes has not been proven."
Astronomers said they were especially impressed by the object's mass, which they said definitely placed it in the size range of a black hole. Explosions of smaller stars often leave a less massive compact remnant called a neutron star.
"Nobody really knows where the neutron-star-black-hole transition occurs," said Dr. Peter M. Garnavich of Notre Dame, another author of the report. "But anything this massive has to be a black hole and not a neutron star."
Dr. Michael R. Garcia of the Harvard-Smithsonian center said the object's position above the dusty galactic plane could lead to its most significant contribution to understanding black holes.
Telescopes will have an exceptionally clear view of the outer and inner edges of the disk of matter forming around the object. The Hubble Space Telescope is expected to be able to observe details of the disk in ultraviolet light.
Astronomers so far have virtually no evidence of what is occurring at the inner edge of a black hole's accretion disk as matter teeters and eventually loses its struggle against a relentless gravitational force so powerful that nothing ever escapes its clutches, not even light.
"This one is going to be a real gem for figuring out what is happening to matter on the brink" of a black hole, Dr. Garcia said.
