Implication of spin constraints by the Event Horizon Telescope on stellar orbits in the Galactic Center

TL;DR

This paper examines how the spin constraints of the supermassive black hole SgrA* from the Event Horizon Telescope impact our understanding of the orbits of nearby stars, revealing tensions between different observational methods.

Contribution

It explores the implications of black hole spin measurements on stellar orbit models and disk formation theories in the Galactic Center.

Findings

Low spin of SgrA* is consistent with stellar disk observations.

High spin measurements challenge existing models of stellar arrangements.

Discrepancies suggest incomplete models of SgrA*'s observed image.

Abstract

The center of the Milky Way hosts the closest supermassive black hole, SgrA$^*$. Decades of near-infrared observations of our Galactic Center have shown the presence of a small population of stars (the so called S-star cluster) orbiting SgrA$^*$, which were recently reported to be arranged in two orthogonal disks. In this case, the timescale for Lense-Thirring precession of S-stars should be longer than their age, implying a low spin for SgrA$^*$. In contrast, the recent results by the Event Horizon Telescope favor a highly-spinning SgrA$^*$, which seem to suggest that the S-stars could not be arranged in disks. Alternatively, the spin of SgrA$^*$ must be small, suggesting that the models for its observed image are incomplete.