Sgr A$^*$: a laboratory to measure the central black hole and cluster parameters

TL;DR

This paper discusses how observing the proper motion of Sgr A* can help constrain the parameters of the surrounding stellar cluster, enabling more accurate tests of General Relativity near the Galactic Center's black hole.

Contribution

It demonstrates that proper motion measurements of Sgr A* can significantly constrain cluster parameters, aiding in the detection of relativistic effects in stellar orbits.

Findings

Proper motion of Sgr A* constrains cluster parameters.

Future periastron shift measurements can determine black hole and cluster properties.

Method to distinguish relativistic effects from classical stellar influences.

Abstract

Several stars orbit around a black hole candidate of mass $3.7\times 10^6$ M$_{\odot}$, in the region of the Galactic Center (GC). Looking for General Relativistic (GR) periastron shifts is limited by the existence of a stellar cluster around the black hole that would modify the orbits due to classical effects that might mask the GR effect. Only if one knows the cluster parameters (its mass and core radius) it is possible to unequivocally deduce the GR effects expected and then test them. In this paper it is shown that the observation of the proper motion of Sgr A$^*$, $v_{Sgr A^*} = (0.4\pm 0.9)$ km s$^{-1}$ (\citealt{reid2004}), could help us to constrain the cluster parameters significantly and that future measurements of the periastron shifts for at least three stars may adequately determine the cluster parameters and the mass of the black hole.