2025/06/05 by Zhao Su, Zhiyuan Li, Su, Zhao +3
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Gravitation Theories #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Relativity and Gravitational Theory
paper · pdf · doi:10.48550/arxiv.2506.04778
openalex publication_date 2025/06/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The central supermassive black hole (SMBH) of the Andromeda galaxy, known as M31*, exhibits dim electromagnetic emission and is inferred to have an extremely low accretion rate for its remarkable mass (∼108~\rm~M_\odot). In this work, we use three-dimensional hydrodynamical simulations to explore a previously untested scenario, in which M31* is fed by the collective stellar mass-loss from its surrounding nuclear star cluster, manifested as a famous eccentric disk of predominantly old stellar populations. The stellar mass-loss is assumed to be dominated by the slow and cold winds from 100 asymptotic giant-branch stars, which follow well-constrained Keplerian orbits around M31* and together provide a mass injection rate of ∼4×10-5\rm~M_\odot~yr-1. The simulations achieve a quasi-steady state on a Myr timescale, at which point a quasi-Keplerian, cool (T∼103-104~\rm K) gas disk extending several parsecs is established. This disk is continuously supplied by the stellar winds and itself feeds the central SMBH. At the end of the simulations at 2 Myr, an accretion rate of ∼2×10-5\rm~M_\odot~yr-1 is found but could vary by a factor of few depending on whether the subdominant gravity of the NSC or a moderate global inflow is included. The predicted X-ray luminosity of ∼1036~\rm erg~s-1, dominated by the hot (T∼107-108~\rm K) plasma within 0.2 parsec of the SMBH, is well consistent with Chandra observations. We conclude that the feeding mechanism of M31* is successfully identified, which has important implications for the working of dormant SMBHs prevalent in the local universe.