Apoastron Shift Constraints on Dark Matter Distribution at the Galactic Center

TL;DR

This paper explores how the analysis of star orbits, especially the apoastron shift of stars like S2, can constrain the distribution and amount of dark matter at the Galactic Center, complementing gamma-ray observations.

Contribution

It introduces a method to use star orbit measurements, particularly apoastron shifts, to improve constraints on dark matter distribution near the Galactic Center.

Findings

Apoastron shift measurements can tighten dark matter constraints.

Star orbit analysis complements gamma-ray data.

Next-generation telescopes will enhance these constraints.

Abstract

The existence of dark matter (DM) at scales of few pc down to $\simeq 10^{-5}$ pc around the centers of galaxies and in particular in the Galactic Center region has been considered in the literature. Under the assumption that such a DM clump, principally constituted by non-baryonic matter (like WIMPs) does exist at the center of our galaxy, the study of the $\gamma$-ray emission from the Galactic Center region allows us to constrain both the mass and the size of this DM sphere. Further constraints on the DM distribution parameters may be derived by observations of bright infrared stars around the Galactic Center. Hall and Gondolo \cite{hallgondolo} used estimates of the enclosed mass obtained in various ways and tabulated by Ghez et al. \cite{Ghez_2003,Ghez_2005}. Moreover, if a DM cusp does exist around the Galactic Center it could modify the trajectories of stars moving around it in a sensible way depending on the DM mass distribution. Here, we discuss the constraints that can be obtained with the orbit analysis of stars (as S2 and S16) moving inside the DM concentration with present and next generations of large telescopes. In particular, consideration of the S2 star apoastron shift may allow improving limits on the DM mass and size.