  We introduce a novel black hole mass function which realistically models the
physics of star formation and pair instability supernova with a minimal number
of parameters. Applying this to all events in the LIGO-Virgo GWTC-2 catalog, we
detect a peak at M_BHMG = 74.8^{+4.3}_{-8.0} MS, followed by a break in the
mass function. Repeating the analysis without the black holes from the event
GW190521, we find this feature at M_BHMG = 55.4^{+3.0}_{-6.1} MS. The latter
result establishes the edge of the anticipated "black hole mass gap" at a value
compatible with the expectation from standard stellar structure theory, while
the former result is ~ 20MS higher, which would have far-reaching implications
if confirmed. Using Bayesian techniques, we establish that our mass function
fits a new catalog of black hole masses approximately as well as the
pre-existing phenomenological mass functions. We also remark on the
implications of these results for constraining or discovering new phenomena in
nuclear and particle physics.
