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

With the advent of adaptive optics on the W. M. Keck 10 m telescope, two signi.cant 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) × 106($ R_{o} \over {8kpc} $)3 M⊙. 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 first detection of spectral absorption lines in one of the high‐velocity stars, S0‐2, one month after its closest approach to the Galaxy's central supermassive black hole. Both Br γ (2.1661 μm) and He I (2.1126 μm) are seen in absorption with equivalent widths and an inferred stellar rotational velocity that are consistent with that of an O8‐B0 dwarf, which suggests that S0‐2 is a massive (∼15 M⊙), young (