SETI Astronomers Find More Evidence Of Black Holes In Galactic Nuclei


Larry Klaes (lklaes@bbn.com)
Tue, 29 Jun 1999 12:28:15 -0400


>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender to owner-astro using -f >Date: Mon, 28 Jun 1999 20:51:08 GMT >From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> >To: astro@lists.mindspring.com >Subject: [ASTRO] Astronomers Find More Evidence Of Black Holes In Galactic Nuclei >Sender: owner-astro@brickbat12.mindspring.com >Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov> > >Ohio State University > >Contact: >Bradley M. Peterson, (614) 292-7886; >Peterson@astronomy.ohio-state.edu > >Written by Pam Frost, (614) 292-9475; Frost.18@osu.edu > >6/28/99 > >ASTRONOMERS FIND MORE EVIDENCE OF BLACK HOLES IN GALACTIC NUCLEI > >COLUMBUS, Ohio -- Astronomers at Ohio State University have discovered >more evidence of the existence of a black hole in the center of a galaxy. > >The astronomers have determined that dense clouds of gas are orbiting the >center of the galaxy NGC 5548 in such a way as to suggest the presence of >a compact, supermassive object at the center. > >Bradley M. Peterson, professor of astronomy at Ohio State, conducted this >work with Amri Wandel, visiting professor at the University of California, >Los Angeles. They presented their results June 1 in Chicago at the annual >meeting of the American Astronomical Society. > >NGC 5548, in the constellation Bootes, is one of a bright class of galaxies >whose massive centers contain active galactic nuclei (AGN). Such nuclei >are so bright, they outshine the stars in the galaxy. > >While AGNs are among the brightest objects in the universe, they are also >very small. Astronomers think their energy comes from gas heating up as >it spirals into a massive black hole at the center. > >One way to tell whether or not the mass in the center of an AGN is a black >hole is to examine the motion of material orbiting the center. This can be >done by studying changes in the light from the AGN over a period of time. > >Peterson and Wandel examined data on NGC 5548 that they collected with >the International Ultraviolet Explorer satellite and ground-based >telescopes in 1989 and 1993. In 1993, this galaxy was also observed >with the Hubble Space Telescope, and these data were also used in this >study. > >They looked at changes in the spectrum of ultraviolet and visible light >from the galaxy, and used that information to calculate the motions of >the clouds and their distance from the center. > >Peterson and Wandel's calculations implied the existence of a small, >supermassive object at the center of NGC 5548 -- a mass equivalent to >70 million suns compressed into a space only about 250 times larger >than the Earth's orbit around the Sun. > >"It's very hard to believe that an object so massive and so small is >anything other than a black hole," said Peterson. > >Peterson likened the orbit of the gas clouds around NGC 5548 to the >motion of the planets around our solar system. Clouds far from the >center of the galaxy move more slowly than clouds closer to the center. >Likewise, the outer planets in our solar system, such as Jupiter or >Saturn, move more slowly in their orbits around the Sun than inner >planets such as Earth or Mars. > >Because the detailed shapes of the clouds orbits cannot be determined >from present data, the black hole mass is rather uncertain, but is >almost certainly in the 10 to 100 solar mass range, Peterson said. > >Actual proof that the central masses in galaxies must be black holes >would require detection of subtle effects predicted by Einstein's theory >of relativity. Such effects would be observable only about 100 times >closer to the central mass than the gas clouds whose motions were >analyzed by Peterson and Wandel. > >"What we're doing is we're heaping on the circumstantial evidence," >said Peterson. "And this is among the best evidence yet." > >With UCLA professor of astronomy Matthew A. Malkan, Peterson and >Wandel have recently extended this work to other AGNs. In the 19 >active galaxies studied so far, the range of masses detected is about >1 million to about 100 million solar masses. > >This work was funded by National Science Foundation and NASA. > >The International Ultraviolet Explorer satellite, which ceased >operations in 1996, resulted from a collaboration among NASA, the >European Space Agency (ESA), and the United Kingdom's Particle >Physics and Astronomy Research Council (PPARC). The Hubble Space >Telescope is a current NASA-ESA project. > > # > >[NOTE: An image supporting this release is available at >http://www.acs.ohio-state.edu/units/research/archive/blkhole.htm] > >



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