# Dark halos around neutron stars and gravitational waves

## TL;DR

This paper explores how dark matter accumulated in neutron stars can alter their structure and tidal polarizability, and how gravitational wave observations from neutron star mergers can constrain such dark matter models.

## Contribution

It introduces constraints on MeV-GeV dark matter models with light vector gauge bosons based on gravitational wave data from neutron star mergers.

## Key findings

- Dark matter in neutron stars can extend to large radii.
- Gravitational wave data constrains dark matter models affecting neutron star structure.
- Presence of dark halos increases variability in neutron star tidal polarizabilities.

## Abstract

We find that a class of models of MeV-GeV dark matter in which dark matter interacts strongly can be constrained by the observation of gravitational waves from neutron star mergers. Trace amounts of dark matter, either produced during the supernova or accreted later, can alter the structure of neutron stars and influence their tidal polarizability. We focus on models of dark matter interacting by the exchange of light vector gauge bosons that couple to a conserved dark charge. In these models, dark matter accumulated in neutron stars can extend to large radii and enhance their tidal polarizability. Gravitational waves detected from the first binary neutron star merger GW170817 places useful constraints on such not-so compact objects. Dark halos, if present, also predict a greater variability of neutron star tidal polarizabilities than expected for ordinary neutron stars.