Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-02-03
J.Astrophys.Astron. 20 (1999) 165-185
Astronomy and Astrophysics
Astrophysics
24 pages, 11 figures, latex, uses aaspp4 style file. To be published in the Journal of Astronomy and Astrophysics (India), pro
Scientific paper
10.1007/BF02702350
Naturally occurring water vapor maser emission at 1.35 cm wavelength provides an accurate probe for the study of accretion disks around highly compact objects, thought to be black holes, in the centers of active galaxies. Because of the exceptionally fine angular resolution, 200 microarcseconds, obtainable with very long baseline interferometry, accompanied by high spectral resolution, < 0.1 km/s, the dynamics and structures of these disks can be probed with exceptional clarity. The data on the galaxy NGC4258 are discussed here in detail. The mass of the black hole binding the accretion disk is 3.9 times 10^7 solar masses. Although the accretion disk has a rotational period of about 800 years, the physical motions of the masers have been directly measured with VLBI over a period of a few years. These measurements also allow the distance from the earth to the black hole to be estimated to an accuracy of 4 percent. The status of the search for other maser/black hole candidates is also discussed.
Greenhill Lincoln J.
Herrnstein James Rezso
Moran James Michael
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