Detectability of accretion-induced bosenovae in the Milky Way

TL;DR

This paper estimates the rate and detectability of axion star collapses, called bosenovae, in the Milky Way, highlighting potential for current and future experiments to observe these rare astrophysical events.

Contribution

It provides the first detailed estimate of axion star collapse rates and discusses their detectability with existing and upcoming axion dark matter experiments.

Findings

Up to 10^{13} bosenovae per galaxy may occur within a year.

Most collapses happen in dense miniclusters with specific overdensity parameters.

Current experiments can potentially detect these axion burst events.

Abstract

We estimate collapse rates of axion stars in our galaxy based on the axion minicluster mass function of the Milky Way dark matter halo. We consider axion-like particles with different temperature evolution of the axion mass, including the QCD axion with $m_a=50\,\mu$eV. Combining estimates for the present-day axion star mass function from our previous work with the axion star accretion model predicted by self-similar growth, we can infer the expected number of bosenovae occurring within the Milky Way. Our estimates suggest that for an observation time of $t_\mathrm{obs}=1\,$yr, the majority of the up to $\sim 10^{13}$ bosenovae per galaxy occur in the densest miniclusters with initial overdensity parameter $\Phi\lesssim 10^4$. We discuss the detectability of such recurring axion bursts within our galactic vicinity and find that, for models with derivative couplings including axion-fermion interactions, potential broadband axion DM experiments can probe a large range of ALP masses $m_a\lesssim 10^{-6}\,$eV and with moderate improvements even the QCD axion case. For axions with non-derivative-type interactions like the axion-photon coupling, our analysis suggests that optimistic predictions with order-one dark matter abundance of axion stars $f_\star \sim 1$ can be probed by dedicated burst searches.