Can the dark matter halo be a collisionless ensemble of axion stars?

TL;DR

This paper investigates whether dark matter halos could be composed of collisionless axion stars, analyzing their properties, interactions with neutron stars, and implications for observational constraints.

Contribution

It provides a detailed calculation of the maximum mass of axion stars and evaluates their potential observational signatures and constraints.

Findings

Maximum mass of axion stars derived from Einstein-Klein-Gordon equations

Energy release from axion-neutron star interactions estimated to be low

Femtolensing data could strongly constrain axion star dark matter scenarios

Abstract

If dark matter is mainly composed of axions, the density distribution can be nonuniformly distributed, being clumpy instead. By solving the Einstein-Klein-Gordon system of a scalar field with the potential energy density of an axionlike particle, we obtain the maximum mass of the self-gravitating system made of axions, called axion stars. The collision of axion stars with neutron stars may release the energy of axions due to the conversion of axions into photons in the presence of the neutron star's magnetic field. We estimate the energy release and show that it should be much less than previous estimates.Future data from femtolensing should strongly constrain this scenario.