Peering at black holes: an eventful look.Twisting space-time and devouring anything--even light--that gets too close, black holes rank among the most bizarre objects in the cosmos. Theory predicts that these gravitational grav·i·ta·tion
a. The natural phenomenon of attraction between physical objects with mass or energy.
b. The act or process of moving under the influence of this attraction.
2. beasts are surrounded by a so-called event horizon, a one-way threshold through which things can fall in but nothing can get out.
Two studies reported at last week's meeting of the American Astronomical Society The American Astronomical Society (AAS, sometimes pronounced "double-A-S") is a US society of professional astronomers and other interested individuals, headquartered in Washington, DC. (AAS) in San Diego provide new evidence for event horizons.
Analyzing a trove of data collected nearly a decade ago by the Hubble Space Telescope Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the clearest view yet obtained of the universe. , astronomers observed what seems to be the last gasp emitted by gaseous material spiraling into Cygnus X-1, a suspected black hole 6,000 light-years from Earth.
Joseph F. Dolan of NASA's Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately 6.5 miles northeast of Washington, D.C. in Greenbelt, Md., and his team found that blobs of hot gas orbiting Cygnus X-1 radiated pulses of ultraviolet light Ultraviolet light
A portion of the light spectrum not visible to the eye. Two bands of the UV spectrum, UVA and UVB, are used to treat psoriasis and other skin diseases. that grew fainter and more rapid and then disappeared.
These fading pulses are just what astronomers expect from gas about to enter an event horizon. Light emitted from the gas grows dimmer dim·mer
1. A rheostat or other device used to vary the intensity of an electric light.
a. A parking light on a motor vehicle.
b. A low beam. because the black hole's gravity shifts the light to longer and longer wavelengths, so the radiation vanishes from view before it actually reaches the event horizon. In contrast, when material crashes into the surface of a star, it releases all its energy and becomes brighter rather than fainter.
The gravitational bending of light causes the radiation to appear pulsed, like a lighthouse beacon, as the gas orbits the black hole thousands of times a second. As the gas spirals ever closer to the hole, it speeds up and its pulses of light quicken until they die out.
William R. Stoeger, a Jesuit priest and astrophysicist now at the University of Arizona's Vatican Observatory Research Group in Tucson, predicted such a scenario in 1980. Although the new study corroborates Stoeger's work, Dolan cautions that his team found just two trains of pulsed ultraviolet light among the myriad data gathered by Hubble's high-speed photometer Photometer
An instrument used for making measurements of light, or electromagnetic radiation, in the visible range. In general, photometers may be divided into two classifications: laboratory photometers, which are usually fixed in position and yield results during the summer of 1992. Astronauts removed the detector in 1993 to make room for the optics required to correct for Hubble's flawed mirror.
"What we have is more in the nature of a lead" than an actual fingerprint of an event horizon, Dolan said at the AAS meeting. Random fluctuations in the Hubble data could mimic the expected swan song of matter falling into a black hole, he notes. Follow-up studies with an ultraviolet detector on Hubble and on craft yet to be launched could firm up the findings, Dolan adds. He and his colleagues are also searching for pulses in data taken by NASA's Rossi X-Ray Timing Explorer The Rossi X-ray Timing Explorer (RXTE) satellite observes the fast-moving, high-energy worlds of black holes, neutron stars, X-ray pulsars and bursts of X-rays that light up the sky and then disappear forever. .
In another study reported at the San Diego meeting, researchers used NASA's Chandra X-Ray Observatory Chandra X-ray Observatory
U.S. X-ray space telescope. It was named after astrophysicist Subrahmanyan Chandrasekhar and was launched into orbit in 1999. Its mirror, with an aperture of 1.2 m (4 ft) and a focal length of 10 m (33 ft), produces unprecedented resolution. to study two types of X-Ray-emitting novas. One type consists of a suspected black hole siphoning gas from a sunlike star that orbits it. In the other type, an ultracompact star called a neutron star devours the nearby gas.
Although both types of nova consumed matter at a similarly slow rate, those suspected of harboring black holes radiated only 1 percent as much light as novas with neutron stars did.
"Seeing just this tiny amount of energy escape from the [candidate] black hole is like sitting upstream, watching water seemingly disappear over the edge," says study collaborator Ramesh Narayan of the Harvard-Smithsonian Center for Astrophysics The Harvard-Smithsonian Center for Astrophysics (CfA) is located in Cambridge, Massachusetts. It consists of the Harvard College Observatory and the Smithsonian Astrophysical Observatory. The Center is located at 60 Garden Street. in Cambridge, Mass. He rates this scarcity of radiation as the strongest evidence yet for event horizons.
Roger D. Blandford of the California Institute of Technology California Institute of Technology, at Pasadena, Calif.; originally for men, became coeducational in 1970; founded 1891 as Throop Polytechnic Institute; called Throop College of Technology, 1913–20. in Pasadena is cautious about both studies. "Although I personally don't doubt that we are dealing with black holes in these systems, I think there are other interpretations of what is going on," he says. For instance, the regions surrounding black holes in the novas could be faint because of some process that expels most of the approaching gas before it reaches the event horizon, Blandford notes.