Coronal radiation of a cusp of spun-up stars and the X-ray luminosity of Sgr A*

Abstract

Chandra has detected optically thin, thermal X-ray emission with a size of ~1 arcsec and luminosity ~10^33 erg/s from the direction of the Galactic supermassive black hole (SMBH), Sgr A*. We suggest that a significant or even dominant fraction of this signal may be produced by several thousand late-type main-sequence stars that possibly hide in the central ~0.1 pc region of the Galaxy. As a result of tidal spin-ups caused by close encounters with other stars and stellar remnants, these stars should be rapidly rotating and hence have hot coronae, emitting copious amounts of X-ray emission with temperatures kT<~ a few keV. The Chandra data thus place an interesting upper limit on the space density of (currently unobservable) low-mass main-sequence stars near Sgr A*. This bound is close to and consistent with current constraints on the central stellar cusp provided by infrared observations. If coronally active stars do provide a significant fraction of the X-ray luminosity of Sgr A*, it should be variable on hourly and daily time scales due to giant flares occurring on different stars. Another consequence is that the quiescent X-ray luminosity and accretion rate of the SMBH are yet lower than believed before.

18 pages, 7 figures. Accepted to MNRAS

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Cited by in corpus (22)

• Hot Accretion Flows Around Black Holes
• Dissecting X-ray-emitting Gas around the Center of our Galaxy
• A Chandra/HETGS Census of X-ray Variability From Sgr A* During 2012
• Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. I. Jet Energetics and the Pristine Parsec-Scale Environment of a Supermassive Black Hole
• Stellar Dynamics and Stellar Phenomena Near A Massive Black Hole
• Chandra-HETGS Observations of the Brightest Flare Seen from Sgr A*
• Physics of the Galactic Center Cloud G2, on its Way towards the Super-Massive Black Hole
• Echoes of multiple outbursts of Sagittarius A* revealed by Chandra
• An Overabundance of Black Hole X-Ray Binaries in the Galactic Center from Tidal Captures
• The Galactic Center Cloud G2 -- a Young Low-Mass Star with a Stellar Wind
• Traces of past activity in the Galactic Centre
• Galactic Center Research: Manifestations of the Central Black Hole
• Three-Dimensional Moving-Mesh Simulations of Galactic Center Cloud G2
• The Megasecond Chandra XVP Observation of NGC 3115: Witnessing the Flow of Hot Gas within the Bondi Radius
• The Quiescent X-ray Spectrum of Accreting Black Holes
• Simulations of Magnetic Fields in Tidally-Disrupted Stars
• Polarization and long-term variability of Sgr A* X-ray echo
• An Inverse Compton Scattering Origin of X-ray Flares from Sgr A*
• XMM-Newton observations of the Galactic Centre Region - I: The distribution of low-luminosity X-ray sources
• The Galactic LMXB Population and the Galactic Centre Region
• Flare emission from Sagittarius A*
• High Energy Emission from the Galactic Center