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Astron. Astrophys. 317, L25-L27 (1997)

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Letter to the Editor

Is Her X-1 really strange?

A.P. Reynolds 1, P. Roche 2 and H. Quaintrell 2

1 Sterrekundig Instituut, P.O. Box 80 000, 3508 TA Utrecht, The Netherlands
2 Astronomy Centre, MAPS, University of Sussex, Falmer, Brighton, BN1 9QH, UK

Received 10 September 1996 / Accepted 15 November 1996


It has recently been proposed that the compact accreting object in the well-studied X-ray binary Hercules X-1 is not a neutron star at all, but a strange star; ie one composed of bulk quark matter. This conclusion has been arrived at by comparing a semi-empirical mass-radius (M-R ) relation for Her X-1 with theoretical M-R curves for neutron and strange stars, and showing that the strange-star models are favoured. However we argue that other data in the literature, and recent observational results (namely new mass and distance estimates) suggest that the hypothesis that Her X-1 is a normal neutron star is not disproved.

Key words: stars:individual:Hercules X-1 – stars:neutron – stars

Send offprint requests to: A.P. Reynolds

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998