Letter to the Editor

Self-bound CFL stars in binary systems: Are they “hidden” among the black hole candidates?

¹ Instituto de Astronomia, Geofísica e Ciencias Atmosféricas Rua do Matão 1226, 05508-900 São Paulo SP, Brazil e-mail: foton@astro.iag.usp.br
² Dipartimento di Fisica “Enrico Fermi”, Università di Pisa via Buonarroti 2, 56127 Pisa, Italy e-mail: lugones@df.unipi.it

Corresponding author: G. Lugones, lugones@df.unipi.it

Received: 16 February 2004
Accepted: 22 May 2004

Abstract

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 ~. 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, and c) impossibility of generating type I bursts because of the complete absence of normal matter crusts at their surfaces. These features caution against a positive identification of event horizons based on the lack of bursts.