SIMBAD references

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.