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Black-hole masses from gas dynamics

Published online by Cambridge University Press:  11 April 2011

F. D. Macchetto
Affiliation:
Space Telescope Science Institute, USA
Mario Livio
Affiliation:
Space Telescope Science Institute, Baltimore
Anton M. Koekemoer
Affiliation:
Space Telescope Science Institute, Baltimore
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Summary

Since the advent of the Hubble Space Telescope (HST), the progress in studying and understanding black holes has been impressive. Early questions regarding the very existence of black holes have been replaced by questions regarding the role that they play in the formation and evolution of galaxies, particularly at early epochs in the universe. However, the apparently well-established relationship between the mass of the black hole and the mass or luminosity of the galactic bulge rests on a relatively small number of direct observations, and while very few doubt that this relationship exists, it is essential to actually measure the properties of a number of black holes over a range of masses and host galaxies. The direct methods adopted to measure black holes in the nearby universe use gas or stellar kinematics to gather information on the gravitational potential in the nuclear region of the galaxy. The stellar-kinematical method has the advantage that stars are present in all galactic nuclei and their motion is always gravitational. The drawbacks are that it requires relatively long observation times in order to obtain high-quality observations, and that stellar-dynamical models are very complex and potentially plagued by indeterminacy. Conversely, the gas-kinematical method is relatively simple; it requires relatively short observation times for the brightest emission-line nuclei, even if not all galactic nuclei present detectable emission lines. However, an important drawback is that noncircular or non-gravitational motions can completely invalidate this method.

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Black Holes , pp. 112 - 135
Publisher: Cambridge University Press
Print publication year: 2011

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