Scalar dark matter vortex stabilization with black holes

TL;DR

This paper explores how black holes can stabilize vortices in scalar dark matter halos, potentially explaining observed galactic spins and addressing vortex instability issues.

Contribution

It introduces a novel mechanism where central black holes stabilize vortices in scalar dark matter, supported by analytic calculations and simulations.

Findings

Black holes can stabilize vortices in scalar dark matter halos.

Vortex stability is enhanced by a central mass comparable to the soliton.

This mechanism may apply to various astrophysical scales, including solar and stellar-mass halos.

Abstract

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.