  The identification of black holes is one of the most important tasks of
modern astrophysics. Candidates have been selected among binary stars based on
a high mass function, and seriously considered when the lower mass limit
exceeds ~ 3 solar masses. More recently the absence of (Type I) thermonuclear
bursts has been advanced as an additional criterion in favor of the black hole
interpretation, since the absence of a solid surface naturally precludes the
accumulation and ignition of accreting material. We discuss in this Letter the
possibility that self-bound stars made of CFL-paired quarks mimic the behavior
of at least the low-mass end black holes as a result of a) higher maximum
masses than ordinary neutron stars b) low steady luminosities due to the bare
surface properties c) impossibility of generating Type I bursts because of the
complete absence of normal matter crusts at their surfaces. These features
caution about a positive identification of event horizons based on the lack of
bursts.
