The Galactic Centre star S2 as a dynamical probe for intermediate-mass black holes

TL;DR

This paper investigates how an intermediate-mass black hole near the Galactic Centre could influence the orbit of star S2, potentially detectable with current observational techniques, providing a new method to identify such black holes.

Contribution

It demonstrates that the orbital perturbations caused by an intermediate-mass black hole can be distinguished from general relativity effects, offering a new way to detect intermediate-mass black holes.

Findings

Perturbations can cause measurable shifts in S2's orbit.

An IBH > 1000 solar masses is detectable by 2018.

Orbital plane changes up to one degree per period.

Abstract

We study the short-term effects of an intermediate mass black hole (IBH) on the orbit of star S2 (S02), the shortest-period star known to orbit the supermassive black hole (MBH) in the centre of the Milky Way. Near-infrared imaging and spectroscopic observations allow an accurate determination of the orbit of the star. Given S2's short orbital period and large eccentricity, general relativity (GR) needs to be taken into account, and its effects are potentially measurable with current technology. We show that perturbations due to an IBH in orbit around the MBH can produce a shift in the apoapsis of S2 that is as large or even larger than the GR shift. An IBH will also induce changes in the plane of S2's orbit at a level as large as one degree per period. We apply observational orbital fitting techniques to simulations of the S-cluster in the presence of an IBH and find that an IBH more massive than about 1000 solar masses at the distance of the S-stars will be detectable at the next periapse passage of S2, which will occur in 2018.