2009MNRAS.400.1632K

We investigate the possibility that stellar mass black holes, with masses in the range of 3.8- 6M_☉, respectively, could be in fact quark stars in the colour-flavour-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 discs around rapidly rotating quark stars and Kerr-type black holes, respectively. Furthermore, we show that the radiation properties of accretion discs 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 disc, may be the key signature to differentiate massive strange stars from the black hole.