Hercules X‐1: an x‐ray binary system with a pulsar

A binary x‐ray source called Hercules X‐1 has been attracting a great deal of attention lately. It turns out to have a pulsar associated with it, thus making it possible to determine directly for the first time the mass of a neutron star. Furthermore, the pulsar has been found to be speeding up, unlike other pulsars, which usually slow down. This result was reported to the Sixth Texas Symposium on Relativistic Astrophysics (held in New York) in December by Harvey Tananbaum of American Science and Engineering.