That is , a quark star is a black hole, while the black hole formation has not collapsed to one point yet.
Pulsars, neutron stars and quark stars are then created based on their mass.
Besides small thermal radii, low-mass quark stars could spin very fast, with a negligible effect of r-mode instability.
Though the maximum masses and corresponding radii are similar, bare strange quark stars and normal neutron stars could be distinguished in the regime of low masses.
