Close Encounters between a Neutron Star and a Main-Sequence Star

TL;DR

This study uses SPH simulations to explore how close tidal encounters between neutron stars and main-sequence stars can lead to the formation of accretion disks, potentially spinning up neutron stars to millisecond periods.

Contribution

It introduces a new simulation-based analysis of tidal interactions between neutron stars and main-sequence stars, highlighting the dependence on a specific dimensionless parameter and implications for pulsar formation.

Findings

Material from disrupted stars forms accretion disks around neutron stars.

Disks can spin up neutron stars to 1 ms periods if fully accreted.

Outcome depends primarily on the parameter eta'.

Abstract

We have examined consequences of strong tidal encounters between a neutron star and a normal star using SPH as a possible formation mechanism of isolated recycled pulsars in globular clusters. We have made a number of SPH simulations for close encounters between a main-sequence star of mass ranging from 0.2 to 0.7 Solar masses represented by an n=3/2 polytrope and a neutron star represented by a point mass. The outcomes of the first encounters are found to be dependent only on the dimensionless parameter eta' = (m/(m+M))^(1/2) (r_min/R_MS)^(3/2) (m/M)^(1/6), where m and M are the masses of the main-sequence star and the neutron star, respectively, r_min the minimum separation between two stars, and R_MS the size of the main-sequence star. The material from the (at least partially) disrupted star forms a disk around the neutron star. If all material in the disk is to be acctreted onto the neutron star's surface, the mass of the disk is enough to spin up the neutron star to spin period of 1 ms.