On the Chandra Detection of Diffuse X-Ray Emission from Sgr A*

Kinematic studies of the stellar motions near Sgr A* have revealed the presence of several million solar masses of dark matter enclosed within 0.015 parsecs of the Galactic Center. However, it is not yet clear what fraction of this material is contained within a single point-like object, as opposed to an extended distribution of orbiting matter (e.g., in the form of neutron stars). Recent Chandra observations suggest that the X-ray emission from this source is partially diffuse. This result provides an important clue that can be used to set some constraints on the mass distribution surrounding the black hole. Here, we develop a simple model in which the diffuse emission is produced by a halo of neutron stars accreting from the gas falling toward the center. We discuss the various accretion mechanisms that are likely to contribute significantly to the X-ray flux, and show that a highly magnetized fraction of old neutron stars may account for the diffuse high-energy source. If this picture is correct, the upper bound to the mass of the central black hole is ≈2.2 × 10⁶ M_⊙. The core radius of the dark cluster must then be ≈0.06 pc. We also discuss the sensitivity of our results to the various assumptions made in our calculations.