The S2 orbit and tidally disrupted binaries: indications for collisional depletion in the Galactic center

TL;DR

The paper investigates how high-velocity stellar collisions can explain the observed orbital precession of the S2 star near Sagittarius A*, suggesting collisional depletion shapes the dense stellar cluster in the Galactic center.

Contribution

It introduces the idea that collisional depletion via destructive collisions is necessary to reconcile observed stellar precession with dense cluster models.

Findings

Collisional depletion is required if star capture rate exceeds a few 10^{-6} per year.

Finite star number fluctuations cannot explain the observed precession.

Astrometric data supports collisional depletion as a key process in the Galactic center.

Abstract

The properties of the stellar cluster surrounding Sagittarius A* can be assessed indirectly through the motion of the S-stars. Specifically, the current accuracy to which the prograde precession of the S2 star is measured allows to place significant constraints on the extended mass enclosed by its orbit. We suggest that high velocity destructive collisions (DCs) offer a natural mechanism for depleting the mass inside the S2 orbit, thus allowing to reconcile the measured precession and the existence of a dense stellar cluster. Such a solution is especially necessary when considering that stars are supplied to the inner part of the cluster by both dynamical relaxation and by stars being captured in tight orbits during tidal disruption of binaries. We use analytic arguments and results from simulations to demonstrate that in order to obtain a precession that is consistent with observations, collisional depletion is necessary if the capture rate is greater than a few $10^{-6} yr^{-1}$. We also show that fluctuations arising from the finite number of stars cannot serve as an alternative to DCs for generating consistency with the observed S2 precession. We conclude that astrometric observations of the S-stars provide a meaningful indication that the inner part of our galactic center is shaped by collisional depletion, supporting the hypothesis that DCs occur in galactic nuclei at an astrophysically significant rate.