The Disc Accretion in Gravitational Field of a Rapidly Rotating Neutron Star with a Rotationally Induced Quadrupole Mass Distribution

TL;DR

This paper investigates how the quadrupole mass distribution of a rapidly rotating neutron star influences accretion processes and energy release, using a new exact gravitational solution and considering various equations of state.

Contribution

It introduces a new exact vacuum solution for the star's gravitational field that accounts for rotationally induced quadrupole moments and applies it to accretion scenarios.

Findings

Quantifies the impact of quadrupole moments on accretion energy release.

Provides a model matching numerical data for marginally stable orbit and redshift.

Analyzes different neutron star equations of state.

Abstract

We analyze the effect of the quadrupole component in the mass distribution of a rapidly rotating neutron star on energy release in the boundary layer on the surface of the accreting star and in the accretion disk in the cases where the stellar radius is smaller (or larger) than the radius of the marginally stable circular orbit. We calculate the velocities and trajectories of the particles that fall on the stellar surface from the marginally stable orbit for a low- luminosity accreting source. The corresponding external gravitational field of the star is modeled by a new exact solution of the Einstein equations in vacuum. The parameters of this solution are adjusted by reconciling the numerical data for the radius of the marginally stable orbit and the gravitational redshift of Cook et al. (1994) with the corresponding data in the analytical solution. For various equations of state, we consider 1.4 solar mass normal sequences and maximum mass normal sequences.