Explaining the Orbits of the Galactic Center S-Stars

TL;DR

The paper demonstrates that the random orientations and thermal eccentricity distribution of S-star orbits near the galactic center can be explained by interactions with an intermediate-mass black hole, supporting the IBH migration model.

Contribution

It shows that a mildly eccentric intermediate-mass black hole can naturally produce the observed orbital properties of S-stars, providing evidence for the IBH's role in their dynamics.

Findings

S-star orbital orientations are nearly random.

Eccentricity distribution is approximately thermal, N(e) ~ e.

An IBH with mass >1500 solar masses can produce these properties.

Abstract

The young stars near the supermassive black hole at the galactic center follow orbits that are nearly random in orientation and that have an approximately thermal distribution of eccentricities, N(e) ~ e. We show that both of these properties are a natural consequence of a few million years' interaction with an intermediate-mass black hole (IBH), if the latter's orbit is mildly eccentric and if its mass exceeds approximately 1500 solar masses. Producing the most tightly-bound S-stars requires an IBH orbit with periastron distance less than about 10 mpc. Our results provide support for a model in which the young stars are carried to the galactic center while bound to an IBH, and are consistent with the hypothesis that an IBH may still be orbiting within the nuclear star cluster.