2006ApJ...644L..45P

The globular cluster G1 (Mayall II) in M31 is the most massive (∼10⁷ M_☉) stellar cluster in the Local Group, and it has the highest central velocity dispersion (∼28 km/s). It has been claimed to host a central ∼20,000 M_☉black hole, but these claims have been controversial. We investigate here the XMM-Newton detection of X-ray emission from G1 at a level of L_X~2x10³⁶ ergs/s. This emission could be the result of Bondi-Hoyle accretion of ionized cluster gas by a central black hole, or it could be produced by a conventional low-mass X-ray binary. A precise localization of the X-ray emission, which is not possible with the current XMM data, could distinguish between these possibilities. While such a measurement may be difficult, it is of sufficient potential importance to pursue.