  The recent detection of a gamma-ray flux from the direction of the Galactic
center by EGRET on the Compton GRO raises the question of whether this is a
point source (possibly coincident with the massive black hole candidate Sgr A*)
or a diffuse emitter. Using the latest experimental particle physics data and
theoretical models, we examine in detail the gamma-ray spectrum produced by
synchrotron, inverse Compton scattering and mesonic decay resulting from the
interaction of relativistic protons with hydrogen accreting onto a point-like
object. Such a distribution of high-energy baryons may be expected to form
within an accretion shock as the inflowing gas becomes supersonic. This
scenario is motivated by hydrodynamic studies of Bondi-Hoyle accretion onto Sgr
A*, which indicate that many of its radiative characteristics may ultimately be
associated with energy liberated as this plasma descends down into the deep
potential well. Earlier attempts at analyzing this process concluded that the
EGRET data are inconsistent with a massive point-like object. Here, we
demonstrate that a more careful treatment of the physics of p-p scattering
suggests that a ~10^6 solar mass black hole may be contributing to this
high-energy emission.
