The case for a massive black hole in the center of the Galaxy is reassessed using improved modeling techniques and observational data. A dark mass of ~2 ×10 6 M⊙ is present within 0.2 pc of the Galactic center. However, the available data can be modeled, without appealing to a massive black hole, using an extended distribution of dark stellar remnants (neutron stars and stellar mass black holes) provided that the stellar initial mass function in the central parsec is deficient in stars less massive than ~1 M⊙. Such a situation may be a natural consequence of repeated gas build-up followed by starbursts in the central region. A clear distinction between this and the massive central black hole model cannot be made using red giant tracers outside 0.2 pc due to uncertainties in the radial velocity dispersion distribution. The cluster of massive early-type emission-line stars in the central parcsec more effectively probe the mass distribution close to Sgr A *, but their small number and partial rotational support complicate mass determinations. Proper motion determinations for stars within 0.5' of Sgr A * may be the most effective means of unambiguously determining the mass distribution in the immediate vicinity of the Galactic center.

• MCGREGOR PETER J.(Mount Stromlo and Siding Spring Observatories, Institute of Advanced Studies, The Australian National University)