The Link between Warm Molecular Disks in Maser Nuclei and Star Formation near the Black Hole at the Galactic Center

The discovery of hundreds of young, bright stars within a parsec from themassive black hole at the center of the Galaxy presents a challenge to starformation theories. The requisite Roche densities for the gravitationalcollapse of gas clouds are most naturally achieved in accretion disks. Thewater maser sources in Keplerian rotation in the nuclei of NGC4258, NGC1068,and the Circinus galaxy indicate the presence of warm, extended, molecularaccretion disks around black holes similar in mass to the one at the Galacticcenter. Here we argue that the current conditions in the maser nuclei, andthose near the Galactic center, represent two consecutive, recurrent phases inthe life cycle of the nucleus of a typical gas-rich spiral bulge. The warmmolecular disks that give rise to the observed maser emission fragment intostellar-size objects. The stellar masses, their orbital geometry, and the totalnumber of stars thus formed are consistent with the values identified at theGalactic center. The stars tend to form in compact groups resembling the IRS 13complex that dominates the stellar light in the neighborhood of the black hole.Comment: ApJ Letters, in pres