  Galaxies and their dark-matter halos are commonly presupposed to spin. But it
is an open question how this spin manifests in halos and soliton cores made of
scalar dark matter (SDM, including fuzzy/wave/ultralight-axion dark matter).
One way spin could manifest in a necessarily irrotational SDM velocity field is
with a vortex. But recent results have cast doubt on this scenario, finding
that vortices are generally unstable except with substantial repulsive
self-interaction. In this paper, we introduce an alternative route to
stability: in both (non-relativistic) analytic calculations and simulations, a
black hole or other central mass at least as massive as a soliton can stabilize
a vortex within it. This conclusion may also apply to AU-scale halos bound to
the sun and stellar-mass-scale Bose stars.
