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

Free access article

Issue		A&A Volume 422, Number 1, July IV 2004


Page(s)		L1 - L4
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20040180

A&A 422, L1-L4 (2004)
DOI: 10.1051/0004-6361:20040180

Letter

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

J. E. Horvath¹ and G. Lugones²

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

(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 ~ $3 ~ M_{\odot}$ . 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.

Key words: X-ray binary systems -- black holes -- thermonuclear bursts -- CFL stars

Offprint request: G. Lugones, lugones@df.unipi.it

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