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NSF ASTRONOMERS DISCOVER SUPERMASSIVE BLACK HOLE IN THE GALAXY NGC 3115

 NSF ASTRONOMERS DISCOVER SUPERMASSIVE BLACK HOLE
 IN THE GALAXY NGC 3115
 WASHINGTON, July 9 /PRNewswire/ -- National Science Foundation (NSF) astronomers have reported the discovery of a supermassive black hole in the galaxy NGC 3115, based on observations that directly measure the galaxy's mass.
 This black hole has the mass of 1 billion suns but does not emit measurable light. It is 100 times more massive than any other black hole that has been detected and "weighed."
 The results are reported in the July 10 issue of The Astrophysical Journal by John Kormendy (Institute for Astronomy, University of Hawaii) and Douglas Richstone (University of Michigan).
 Their observations consist of high-resolution measurements of the galaxy's center taken with the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii. These were used to measure velocities of stars via the Doppler shift, the redshift of the wavelength (or color) of light produced by the motion of stars away from us. Kormendy and Richstone found that the nucleus of NGC 3115 spins very rapidly. Random velocities of stars also increase dramatically toward the center. Both observations allow astronomers to "weigh" the galaxy. They show that a large mass is present in the nucleus; otherwise it would fly apart.
 A computer analysis of stellar orbits was carried out in Michigan ruling out alternatives that might have explained the observations without a black hole. Most of the stellar material is dark, proving that the galaxy hides a central object that is tiny but that is not made of ordinary stars. "It is probably a black hole," says Kormendy.
 The technique is unique because it directly detects the gravitational influence of a black hole on nearby stars. Only two other nuclei have similarly been "weighed;" the Andromeda Galaxy and its neighbor M 32. Both are known to contain black holes with masses of a million to 10 million suns. The black hole in NGC3115 is 100 times more massive. "To grow to 1 billion solar masses, it 'swallowed' so much material that it could have been brighter than the brightest galaxies at one time," Kormendy says. "This black hole candidate is massive enough to have powered a quasar."
 These findings strengthen the view that quasars -- the brightest objects in the universe -- are powered by accretion onto massive black holes. Quasars are so luminous that they can be detected from farther away than any other object. In many cases, their light has been traveling toward us for most of the age of the universe. Therefore we observe quasars as they were long ago. As a result, astronomers can infer how a quasar evolved over time.
 Quasars were numerous when the universe was one-quarter of its present age. Since then, most of them have died out. Therefore dead quasars should be "hiding" in many nearby galaxies. Quasar energies imply that the dead remnants should have masses of a billion suns. The discovery of a supermassive black hole is a crucial confirmation of the black hole accretion theory of quasars.
 The galaxy is visible in moderate-sized amateur telescopes as a faint fuzzy patch in the constellation Sextans (The Sextant). But at a distance of 30 million light years, NGC 3115 is more than 10 times farther from us than the Andromeda galaxy or M 32. In reality, it is several times bigger than our own Milky Way. But its stars are mostly old, it contains virtually no gas, and its nucleus is extremely inactive. The growth of the black hole and the nuclear activity that it feeds are over, unless additional stars wander too close to the center. If that happens, the nucleus is expected to experience a brief but energetic rebirth.
 Although these findings support the current general picture of quasars, they also highlight a number of unresolved issues. "We have only a very speculative idea of how supermassive black holes form," Richstone said. The processes that control their growth, and those that later turn them off, are poorly understood. Finding nearby black holes is crucial to further progress. NGC 3115 provides a billion-solar-mass example.
 The National Science Foundation is an independent agency of the federal government established in 1950 to promote and advance scientific progress in the United States. NSF accomplishes its mission primarily by competitively awarding grants to educational institutions for research and education in the sciences, mathematics, and engineering.
 This and other information is available electronically on STIS, NSF's Science and Technology Information System. For more information about STIS contact the Publications Section at 202-357- 7861 and request the "STIS" Flyer," NSF Publication No. 91-10, or send an E-mail message to "stisinfo(at)nsf.gov" (INTERNET) or "stisinfo(at)NSF" (BITNET).
 -0- 7/9/92
 /CONTACT: Cheryl Dybas of the National Science Foundation, 202-357-9498/ CO: National Science Foundation ST: District of Columbia IN: SU:


DC -- DC008 -- 7820 07/09/92 11:07 EDT
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