  We explore the possibility that GW150914, the binary black hole merger
recently detected by Advanced LIGO, was formed by gravitational interactions in
the core of a dense star cluster. Using models of globular clusters with
detailed $N$-body dynamics and stellar evolution, we show that a typical
cluster with a mass of $3\times10^5M_{\odot}$ to $6\times10^5M_{\odot}$ is
optimal for forming GW150914-like binary black holes that will merge in the
local universe. We identify the most likely dynamical processes for forming
GW150914 in such a cluster, and we show that the detection of GW150914 is
consistent with the masses and merger rates expected for binary black hole
mergers from globular clusters. Our results show that dynamical processes
provide a significant and well-understood pathway for forming binary black hole
mergers in the local universe. Understanding the contribution of dynamics to
the binary black hole merger problem is a critical step in unlocking the full
potential of gravitational-wave astronomy.
