Annu. Rev. Astron. Astrophys. 1995. 33: 581-624 Copyright © 1995 by Annual Reviews Inc. All rights reserved

KEY WORDS: black holes, dead quasars, galactic dynamics, galactic nuclear activity

ABSTRACT. Dynamical searches reveal central dark objects with masses ~ 10⁶ to 10^9.5 M in the Galaxy, M31, M32, M87, NGC 3115, NGC 3377, NGC 4258, and NGC 4594. Indirect arguments suggest but do not prove that these are supermassive black holes (BHs) like those postulated as quasar engines. This paper reviews dynamical search techniques, the robustness of the evidence, and BH demographics. Stellar-dynamical evidence is generally more robust than gas-dynamical evidence (gas velocities can be nongravitational), but gas measurements reach closer to the Schwarzschild radius, and in NGC 4258 they show a Keplerian rotation curve. A statistical survey finds BHs in ~ 20% of nearby E-Sbc galaxies, consistent with predictions based on quasar energetics. BH masses are proportional to the mass of the bulge component. Most candidates are inactive; in some cases, the abundance of fuel is not easily reconciled with BH starvation. Flashes caused by the accretion of individual stars may provide a test of the BH picture.

Table of Contents

INTRODUCTION

PRESENT STATUS OF THE BLACK HOLE SEARCH

CUSPY DENSITY PROFILES ARE NOT EVIDENCE FOR BLACK HOLES

STELLAR-DYNAMICAL BLACK HOLE SEARCHES

Search Technique

M31 (M_BH 3 x 10⁷ M)

NGC 3115 (M_BH 1 x 10⁹ M)

M32 (M_BH 2 x 10⁶ M)

NGC 4594, The Sombrero Galaxy (M_BH 5 x 10⁸ M)

The Galaxy (M_BH 2 x 10⁶ M)

NGC 3377 (M_BH 8 x 10⁷ M)

M33 (M_BH 10⁴ M)

GAS-DYNAMICAL BLACK HOLE SEARCHES

M87 (M_BH 3 x 10⁹ M)

NGC 4258 (M_BH 4 x 10⁷ M)

BLACK HOLE DEMOGRAPHICS

ARE MDOs TOO BLACK TO BE BLACK HOLES?

CONCLUSION

REFERENCES