General Relativistic Simulations of Accretion Induced Collapse of Neutron Stars to Black Holes

TL;DR

This study uses full 3D general relativity simulations to analyze how accretion disks influence neutron star collapse into black holes, highlighting differences in electromagnetic signals that could help identify such events.

Contribution

First 3D general relativistic simulations of accretion-induced neutron star collapse, revealing electromagnetic signatures distinguishable from vacuum collapse.

Findings

Electromagnetic signals differ between accretion-induced and vacuum collapses.

Post-collapse accretion onto the black hole can power short gamma-ray bursts.

Gravitational wave signals are similar for both collapse types, but electromagnetic signals vary.

Abstract

Neutron stars (NSs) in the astrophysical universe are often surrounded by accretion disks. Accretion of matter onto an NS may increase its mass above the maximum value allowed by its equation of state, inducing its collapse to a black hole (BH). Here we study this process for the first time, in three-dimensions, and in full general relativity. By considering three initial NS configurations, each with and without a surrounding disk (of mass ~7% M_{NS}), we investigate the effect of the accretion disk on the dynamics of the collapse and its imprint on both the gravitational wave (GW) and electromagnetic (EM) signals that can be emitted by these sources. We show in particular that, even if the GW signal is similar for the accretion induced collapse (AIC) and the collapse of an NS in vacuum (and detectable only for Galactic sources), the EM counterpart could allow us to discriminate between these two types of events. In fact, our simulations show that, while the collapse of an NS in vacuum leaves no appreciable baryonic matter outside the event horizon, an AIC is followed by a phase of rapid accretion of the surviving disk onto the newly formed BH. The post-collapse accretion rates, on the order of ~10^{-2} M_{sun} s^{-1}, make these events tantalizing candidates as engines of short gamma-ray bursts.