Prompt merger collapse and the maximum mass of neutron stars

TL;DR

This study uses hydrodynamical simulations to explore the threshold mass for prompt black hole formation after neutron star mergers, revealing a strong correlation with the stars' compactness and potential for constraining neutron star properties.

Contribution

The paper provides the first comprehensive analysis of how the threshold mass for prompt collapse depends on the equation of state and compactness of neutron stars.

Findings

Threshold mass exceeds maximum non-rotating mass by 30-70%.

Threshold mass-to-maximum mass ratio correlates with compactness.

Results can help constrain neutron star properties from observations.

Abstract

We perform hydrodynamical simulations of neutron-star mergers for a large sample of temperature-dependent, nuclear equations of state, and determine the threshold mass above which the merger remnant promptly collapses to form a black hole. We find that, depending on the equation of state, the threshold mass is larger than the maximum mass of a non-rotating star in isolation by between 30 and 70 per cent. Our simulations also show that the ratio between the threshold mass and maximum mass is tightly correlated with the compactness of the non-rotating maximum-mass configuration. We speculate on how this relation can be used to derive constraints on neutron-star properties from future observations.