Accretion from Winds of Red Giant Branch Stars May Reveal the Supermassive Black Hole in Leo I

Abstract

A supermassive black hole (SMBH) of $\sim 3\times 10^6{\mathrm{M}}_{\odot }$ was recently detected via dynamical measurements at the center of the dwarf galaxy Leo I. Standing $\sim 2$ orders of magnitude above standard scaling relations, this SMBH is hosted by a galaxy devoid of gas and with no significant star formation in the last $\sim 1$ Gyr. This detection can profoundly impact the formation models for black holes and their hosts. We propose that winds from a population of $\sim 100$ evolved stars within the Bondi radius of the SMBH produce a sizable accretion rate, with Eddington ratios between $9\times 10^{-8}$ and $9\times 10^{-7}$, depending on the value of the stellar mass loss. These rates are typical of SMBHs accreting in advection-dominated accretion flow (ADAF) mode. The predicted spectrum peaks in the microwaves at $\sim 0.1-1$ THz ($300-3000\mu \mathrm{m}$) and exhibits significant variations at higher energies depending on the accretion rate. We predict a radio flux of $\sim 0.1$ mJy at $6$ GHz, mildly dependent on the accretion properties. Deep imaging with Chandra, VLA, and ALMA can confirm the presence of this SMBH and constrain its accretion flow.

Accepted for publication in The Astrophysical Journal Letters. 6 pages, 2 figures

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• Observational Signatures of Massive Black Hole Progenitor Pathways: Could Leo I a Smoking Gun?
• Over-massive Central Black Holes in the Cosmological Simulations ASTRID and Illustris TNG50
• Extreme Tidal Stripping May Explain the Overmassive Black Hole in Leo I: a Proof of Concept
• Accretion of the degenerate Fermi gas onto a Reissner-Nordström black hole
• Discovery of a Dense Association of Stars in the Vicinity of the Supermassive Black Hole Sgr A*