Other
Scientific paper
Apr 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aps..apr.c3001m&link_type=abstract
American Physical Society, April Meeting, April 28 - May 1, 2001 Washington, DC Bulletin of the American Physical Society, Vol.
Other
Scientific paper
Supermassive black holes (10^6.5 M_sun < M_BH < 10^9.5M_sun) appear to be present at the center of every nearby galaxy including our own. Black hole masses can be determined in a number of ways. Direct measurement of the orbital velocity of stars or gas on sub-parsec scales in galactic nuclei gives M_BH via Kepler's laws. In active galaxies, M_BH can be estimated via ``reverberation mapping,'' a technique that measures the gravitational influence of the black hole on the motion of gas within about 0.01 parsec. The mean mass density of black holes can also be estimated from observations of the integrated quasar light at optical or X-ray wavelengths, after making an assumption about the efficiency with which gravitational energy is converted into radiation during the quasar epoch. Until recently, all of these estimates were consistent expect for the first, which gave a mean ratio M_BH/M_Galaxy an order of magnitude greater than the others. However the discovery of a strong empirical correlation between black hole mass and galaxy velocity dispersion, the ``M_BH-Sigma relation,'' has resolved the discrepancy by showing that many of the black hole mass estimates in nearby galaxies were too large. All methods now give a consistent value of 1-2 x 10-3 for the mean ratio of black hole mass to luminous galaxy mass in the nearby universe. Implications for the formation history of supermassive black holes will be discussed.
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