Strangeon Ergostars

TL;DR

This study explores the viability of ergostars as central engines for short gamma-ray bursts using a strangeon matter equation of state, revealing a large stable parameter space and sufficient energy for powering sGRBs.

Contribution

It demonstrates that strangeon matter allows for stable ergostars without extreme conditions, unlike conventional neutron star models, revitalizing the ergostar hypothesis for sGRBs.

Findings

Stable ergostars exist with strangeon matter EOS.

Extractable energy can reach about 0.01 solar masses.

Supports ergostars as viable sGRB central engines.

Abstract

The nature of the central engine powering short gamma-ray bursts (sGRBs) in binary neutron star (BNS) mergers remains a key open question in the era of multi-messenger astronomy. The ergostar hypothesis, that a rapidly rotating star with an ergoregion drives the relativistic jet, offers an alternative explanation to the black hole-accretion disk paradigm. However, previous studies based on conventional neutron star equations of state (EOSs) have shown that dynamically stable ergostars do not exist unless very extreme EOS or rotation are adopted, casting significant doubt on their astrophysical viability in reality. In this work, however, we examine this hypothesis using a phenomenological EOS of strangeon matter, i.e., condensed matter with nucleon-like units for three flavors of quarks. By constructing a large suite of uniformly rotating equilibrium models, we systematically investigate the parameter space of the stable ergostars and calculate their maximum extractable energy. In contrast to the case of conventional EOSs, we demonstrate that strangeon matter supports a vast and robust parameter space for dynamically stable ergostars, even without requiring differential rotation. We find that the extractable rotational energy from these configurations can be on the order of $0.01 M_\odot$, a reservoir sufficient to power a typical sGRB. Our results revitalize the ergostar as a viable central engine for sGRB, suggesting that BNS merger remnants composed of exotic matter could play a crucial, previously underestimated role in high-energy astrophysics.