Can accreting isolated neutron stars be detected?

TL;DR

This study models the population of isolated neutron stars in the Milky Way, highlighting how uncertainties in their spin-down and accretion processes affect their detectability with current X-ray surveys.

Contribution

It introduces more detailed models of the interstellar medium and neutron star evolution, providing new estimates for the number of detectable accreting isolated neutron stars.

Findings

Number of detectable accreting neutron stars could reach a few thousand with high accretion efficiency.

Uncertainties in the propeller stage significantly impact the predicted population.

Future Gaia observations could help resolve key uncertainties.

Abstract

We perform population synthesis modeling of isolated neutron stars in the Milky Way over its lifetime. Compared with previous studies, we use more detailed models of the interstellar medium and the magneto-rotational evolution of neutron stars. We demonstrate that presently, the spin-down rate at the propeller stage is the main uncertain factor that influences the number of accreting isolated neutron stars. If the propeller stage duration allows neutron stars to begin accreting matter from the interstellar medium and if the efficiency of accretion is high, then the number of accreting isolated neutron stars in eROSITA data can reach ~a few thousand. Still, uncertainties in spin-down at the propeller stage and in the accretion process can drastically decrease this number. We suggest that future observations of neutron stars in wide low-mass binaries recently discovered by Gaia can clarify these issues.