Gas Accretion by Star Clusters and the Formation of Ultraluminous X-ray Sources from Cusps of Compact Remnants

TL;DR

This paper proposes that the overabundance of ultra-luminous X-ray sources in certain star clusters can be explained by gas accretion onto neutron stars, without requiring intermediate mass black holes.

Contribution

It introduces an alternative explanation for ULXs involving gas accretion in star clusters, challenging the IMBH hypothesis.

Findings

Gas density is enhanced by cluster potential, leading to high accretion rates.

Aggregate X-ray luminosity from neutron stars can exceed 10^{39} erg/s.

Observational tests can distinguish between IMBHs and neutron star cusps.

Abstract

Here we show that the overabundance of ultra-luminous, compact X-ray sources (ULXs) associated with moderately young clusters in interacting galaxies such as the Antennae and Cartwheel can be given an alternative explanation that does not involve the presence of intermediate mass black holes (IMBHs). We argue that gas density within these systems is enhanced by the collective potential of the cluster prior to being accreted onto the individual cluster members and, as a result, the aggregate X-ray luminosity arising from the neutron star cluster members can exceed $>10^{39} {\rm erg s^{-1}}$. Various observational tests to distinguish between IMBHs and accreting neutron star cusps are discussed.