On the origin of the B-stars in the galactic center

Abstract

We present a new directly observable statistic that uses sky position (x, y) and proper motion (vx , vy ) of stars near the massive black hole in the Galactic center to identify populations with high orbital eccentricities. It is most useful for stars with large orbital periods for which dynamical accelerations are difficult to determine. We apply this statistic to a data set of B-stars with a projected radii 0.″1 < p < 25″ (∼0.004-1 pc) from the massive black hole in the Galactic center. We compare the results with those from N-body simulations to distinguish between scenarios for their formation. We find that the scenarios favored by the data correlate strongly with particular K-magnitude intervals, corresponding to different zero-age, main-sequence (MS) masses and lifetimes. Stars with 14 ≲ m K ≲ 15 (15-20 M,tMS = 8-13 Myr) match a disk formation origin well, whereas those with mK ≥ 15 (<15 M, tMS > 13 Myr), if isotropically distributed, form a population that is more eccentric than thermal, which suggests a Hills binary-disruption origin. © 2014. The American Astronomical Society. All rights reserved.