34th Meeting of the AAS Division on Dynamical Astronomy, May 2003
3 Galactic Dynamics
Oral, Monday, May 5, 2003, 1:15-3:55pm,

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[3.02] Invited: Stellar and Gas Dynamics in the Central Parsec of the Galaxy

M. Morris (UCLA)

With a radius of about 1.5 pc, the domain of influence of the supermassive black hole at the center of our Galaxy, which has a radius of about 1.5 pc, is a phenomenologically rich region about which much can be learned from the dynamics of both stars and gas. The radial distribution of the relatively old stars in the central stellar cluster, as well as its core radius, are determined from imaging studies, while statistical analyses of radial velocities and proper motions provide a determination of the enclosed mass. However, the presence of an apparent hole in the red giant distribution has a strong effect on the statistical mass estimations. The early-type stellar population in the central parsec is quite a different matter. First, there is the paradox of how apparently young stars can be present in the region in which the tidal forces of the black hole should have suppressed normal star formation. Potential solutions to this paradox will be discussed, with particular attention paid to whether dynamical friction can cause stars to migrate inwards on a sufficiently short time scale. Second, the dynamics of early-type stars in the central arcsecond (0.04 pc) have lately been providing a great deal of information on the neighborhood of the central black hole. A decade of proper motion studies, combined with recent spectroscopy, now reveal almost complete orbits of some of the stars closest to the central black hole. These orbits yield the black hole mass, its location (to within 1.5 milliarcsec), and a limit on its proper motion. Limits on the orbital precession and on the variation of central mass with periapse distance constrain the extended mass distribution, hypothetically in the form of stellar remnants or dark matter particles (relativistic precession is even less accessible). In fitting orbits simultaneously to the plane-of-sky motions and radial velocities, one additional parameter which can be fit is the Galactic center distance, D. Now consistent with other determinations, the value of D inferred in this way should soon become the most accurate measure available. Gas motion, which can be affected by non-gravitational forces, provides a complementary probe of the central parsec. Several gas streams have been identified, and their dynamics studied, also using both spectroscopic and proper motion measures. A few of these streams -- the Northern and Eastern Arms -- appear to be infalling on predominantly radial orbits. The details of the Northern Arm dynamics, as determined using imaging spectroscopy by Paumard et al. (2003) will be presented. Because it is likely to self-intersect and form a dispersion ring, this feature will presumably lead to a significant accretion episode on a time scale of a few times 104 years, as the gas encounters the black hole.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.