Magnetically supramassive neutron stars

TL;DR

This paper proposes that ultra-strong magnetic fields in neutron star merger remnants can temporarily support masses above the stability limit, leading to a new class of magnetically supramassive neutron stars that survive for years before collapsing.

Contribution

It introduces the concept of magnetically supramassive neutron stars supported by ultra-strong magnetic fields, expanding understanding of post-merger neutron star evolution.

Findings

Magnetically supramassive neutron stars can survive for years before collapsing.

Strong magnetic fields can temporarily support excess mass in neutron stars.

Potential multi-messenger signatures of these objects are discussed.

Abstract

It is commonly believed that neutron stars exceeding the maximum mass limit for stability could be formed in the aftermath of binary neutron star mergers, enjoying a short life of metastability before losing centrifugal support and collapsing to a black hole. It is suggested here that a similar scenario could take place when the remnant's excess mass is supported by an ultra-strong $(\gtrsim 10^{17}\,\mbox{G})$ magnetic field that could be generated during, and shortly after, coalescence. We show that such 'magnetically supramassive' neutron stars could stave off collapse and survive for a few years before their magnetic energy is sufficiently dissipated due to ambipolar diffusion. In addition, we speculate on multi-messenger signatures of such objects and discuss the robustness of our results against limitations placed by neutron superfluidity and magneto-thermal evolution.