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

¹ Israel Arts and Science Academy, Jerusalem 9640801, Israel
² Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel

^★ Corresponding author; shmuel.balberg@mail.huji.ac.il

Received: 2 December 2024
Accepted: 30 January 2025

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 one 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 the measured precession and the existence of a dense stellar cluster to be reconciled. 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 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 the Galactic center is shaped by collisional depletion, supporting the hypothesis that DCs occur in galactic nuclei at an astrophysically significant rate.