Can stellar mass black holes be quark stars?

TL;DR

This paper explores whether stellar mass black holes could actually be quark stars in the CFL phase, examining their properties, potential observational signatures, and how to distinguish them from true black holes.

Contribution

It proposes that CFL quark stars can mimic black holes in mass and emission properties, offering a new perspective on compact object identification.

Findings

CFL quark stars can reach masses similar to stellar black holes.

Accretion disk emissions around CFL quark stars are similar to those around black holes.

Distinctive low luminosity and high temperature bremsstrahlung spectra may differentiate quark stars from black holes.

Abstract

We investigate the possibility that stellar mass black holes, with masses in the range of $3.8M_{\odot}$ and $6M_{\odot}$, respectively, could be in fact quark stars in the Color-Flavor-Locked (CFL) phase. Depending on the value of the gap parameter, rapidly rotating CFL quark stars can achieve much higher masses than standard neutron stars, thus making them possible stellar mass black hole candidates. Moreover, quark stars have a very low luminosity and a completely absorbing surface - the infalling matter on the surface of the quark star is converted into quark matter. A possibility of distinguishing CFL quark stars from stellar mass black holes could be through the study of thin accretion disks around rapidly rotating quark stars and Kerr type black holes, respectively. Furthermore, we show that the radiation properties of accretion disks around black holes and CFL quark stars are also very similar. However, strange stars exhibit a low luminosity, but high temperature bremsstrahlung spectrum, which, in combination with the emission properties of the accretion disk, may be the key signature to differentiate massive strange stars from black hole.