Full Three Dimensional Orbits For Multiple Stars on Close Approaches to the Central Supermassive Black Hole

Astrophysics, abstract
astro-ph/0303151

From: A. M. Ghez <ghez@astro.ucla.edu>

Date: Fri, 7 Mar 2003 00:26:43 GMT   (108kb)

Authors:
A. M. Ghez,
E. Becklin,
G. Duchene,
S. Hornstein,
M. Morris,
S. Salim,
A. Tanner

Comments: 7 pages, 5 figures (abridged abstract)

Journal-ref: Astron. Nachr., Vol. 324, No. S1 (2003), Special Supplement “The
central 300 parsecs of the Milky Way”, Eds. A. Cotera, H. Falcke, T. R.
Geballe, S. Markoff

With the advent of adaptive optics on the W. M. Keck 10 m telescope, two
significant steps forward have been taken in building the case for a
supermassive black hole at the center of the Milky Way and understanding the
black hole’s effect on its environment. Using adaptive optics and speckle
imaging to study the motions of stars in the plane of sky with +-~2 mas
precision over the past 7 years, we have obtained the first simultaneous
orbital solution for multiple stars. Among the included stars, three are newly
identified (S0-16, S0-19, S0-20). The most dramatic orbit is that of the newly
identified star S0-16, which passed a mere 60 AU from the central dark mass at
a velocity of 9,000 km/s in 1999. The orbital analysis results in a new central
dark mass estimate of 3.6(+-0.4)x10^6(D/8kpc)^3 Mo. This dramatically
strengthens the case for a black hole at the center of our Galaxy, by confining
the dark matter to within a radius of 0.0003 pc or 1,000 Rsh and thereby
increasing the inferred dark mass density by four orders of magnitude compared
to earlier estimates.

With the introduction of an adaptive-optics-fed spectrometer, we have
obtained the spectra of these high-velocity stars, which suggest that they are
massive (~15 Mo), young (<10 Myr) main sequence stars. This presents a major
challenge to star formation theories, given the strong tidal forces that
prevail over all distances reached by these stars in their current orbits and
the difficulty in migrating these stars inward during their lifetime from
further out where tidal forces should no longer preclude star formation.

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