Instability of rotating Bose stars

TL;DR

This paper investigates the stability of rotating Bose stars composed of axion-like dark matter, demonstrating that most are unstable unless they have strong repulsive self-interactions, with implications for their longevity and structure.

Contribution

The study provides analytical and numerical analysis of rotating Bose stars' stability, revealing instability for most cases and stability only under strong repulsive self-interactions.

Findings

Rotating Bose stars with nonzero angular momentum are generally unstable.

Strong repulsive self-interactions can stabilize the $l=1$ Bose star.

Unstable stars decay by shedding particles and angular momentum, forming complex configurations.

Abstract

Light bosonic (axion-like) dark matter may form Bose stars - clumps of nonrelativistic Bose-Einstein condensate supported by self-gravity. We study rotating Bose stars composed of condensed particles with nonzero angular momentum $l$. We analytically prove that these objects are unstable at arbitrary $l \ne 0$ if particle self-interactions are attractive or negligibly small. They decay by shedding off the particles and transporting the angular momentum to the periphery of the system until a Saturn-like configuration appears: one (or several) spin-zero Bose stars and clouds of diffuse particles orbit around the mutual center. In the case of no self-interactions we calculate the profiles and dominant instability modes of the rotating stars: numerically at $1 \leq l\leq 15$ and analytically at $l\gg 1$. Notably, their lifetimes are always comparable to the inverse binding energies; hence, these objects cannot be considered long-living. Finally, we numerically show that in models with sufficiently strong repulsive self-interactions the Bose star with $l=1$ is stable.