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

TL;DR

This paper introduces a new observable statistic to analyze stellar populations near the Galactic center's black hole, revealing different formation scenarios for B-stars based on their orbital eccentricities and magnitudes.

Contribution

The study develops a novel statistic for identifying high-eccentricity stellar populations using sky position and proper motion, applied to B-stars in the Galactic center.

Findings

Stars with 14 < mK < 15 likely formed in a disk.

Stars with mK > 15 show eccentricities consistent with Hills binary-disruption.

Different stellar masses correlate with distinct formation scenarios.

Abstract

We present a new directly-observable statistic which uses sky position and proper motion of stars near the Galactic center massive black hole 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 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 < mK < 15 (15 - 20 solar masses, t_{MS} = 8-13 Myr) match well to a disk formation origin, while those with mK > 15 (<15 solar masses, t_{MS} >13 Myr), if isotropically distributed, form a population that is more eccentric than thermal, which suggests a Hills binary-disruption origin.