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10.1. The nuclear star cluster of the Milky Way: star formation and central dark mass

Published online by Cambridge University Press:  25 May 2016

R. Genzel  and
A. Eckart
R. Genzel
Affiliation:
Max-Planck Institut für extraterrestrische Physik Garching, FRG
A. Eckart
Affiliation:
Max-Planck Institut für extraterrestrische Physik Garching, FRG

Abstract

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High spatial resolution, near-infrared imaging and spectroscopy of the nuclear star cluster obtained in the last few years have given key new insights about the structure, evolution and mass distribution in the Milky Way Center. The central parsec is powered by a cluster of hot, massive stars. Their characteristics imply that there was an active phase of star formation a few million years ago, probably triggered by the infall and collapse of a very dense gas cloud. Other such starburst episodes may have taken place between 100 and 300 million years ago. Measurements of radial and proper motions for more than 200 stars show that stellar velocities increase with a Kepler law down to a scale of a light week from the compact radio source Sgr A∗. The data make a compelling case for the presence of a compact, central dark mass of about 2.6×106 M⊙. Simple physical considerations show that this dark mass cannot consist of a stable cluster of stars, stellar remnants or substellar condensations. Energy equipartition requires that at least five percent of the dark mass (≥105 M⊙) must be associated with Sgr A∗ itself and likely is enclosed within less than 8 light minutes. If one accepts these arguments it is hard to escape the conclusion that Sgr A∗ is indeed a massive black hole at the core of the Milky Way.

Type
Part III. Black Holes and Central Activity
Information
Symposium - International Astronomical Union , Volume 184: The Central Regions of the Galaxy and Galaxies , 1998 , pp. 421 - 431
Copyright
Copyright © Kluwer 1998 

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