The S-Star Cluster at the Center of the Milky Way: On the nature of diffuse NIR emission in the inner tenth of a parsec

TL;DR

This study investigates the diffuse near-infrared emission and stellar mass distribution around the Milky Way's central black hole, using imaging and simulations to understand the nature of the S-star cluster and its dark components.

Contribution

It combines observational data with N-body simulations to constrain the stellar and dark mass near Sagittarius A* and assesses the impact of stellar perturbations on star orbits.

Findings

Stellar mass from luminosity is much smaller than the total mass inferred from orbital dynamics.

Diffuse light from faint cluster members is below residual levels after bright stars are removed.

Star blending at 2.2 μm can last for about 3 years due to proper motions.

Abstract

Sagittarius A*, the super-massive black hole at the center of the Milky Way, is surrounded by a small cluster of high velocity stars, known as the S-stars. We aim to constrain the amount and nature of stellar and dark mass associated with the cluster in the immediate vicinity of Sagittarius A*. We use near-infrared imaging to determine the $K_\mathrm{s}$-band luminosity function of the S-star cluster members, and the distribution of the diffuse background emission and the stellar number density counts around the central black hole. This allows us to determine the stellar light and mass contribution expected from the faint members of the cluster. We then use post-Newtonian N-body techniques to investigate the effect of stellar perturbations on the motion of S2, as a means of detecting the number and masses of the perturbers. We find that the stellar mass derived from the $K_\mathrm{s}$-band luminosity extrapolation is much smaller than the amount of mass that might be present considering the uncertainties in the orbital motion of the star S2. Also the amount of light from the fainter S-cluster members is below the amount of residual light at the position of the S-star cluster after removing the bright cluster members. If the distribution of stars and stellar remnants is strongly enough peaked near Sagittarius A*, observed changes in the orbital elements of S2 can be used to constrain both their masses and numbers. Based on simulations of the cluster of high velocity stars we find that at a wavelength of 2.2 $\mu$m close to the confusion level for 8 m class telescopes blend stars will occur (preferentially near the position of Sagittarius A*) that last for typically 3 years before they dissolve due to proper motions.