Heartbeats of a neutron star

摘要

Neutron stars are remnants of the supernova explosions of stars more massive than our Sun. Their dense cores are thought to consist mostly of neutrons, but may contain exotic states of matter that are unknown elsewhere in the Universe. Neutron stars are often found in binary systems, partnered by a surviving star. Hot gas spirals onto the neutron star from its stellar companion, dragged in by the gravity of the denser object, and X-rays are emitted (Fig. 1, overleaf). Observations by the Rossi X-ray Timing Explorer (RXTE) satellite and other spacecraft during the past decade have shown that these X-rays carry three types of nearly periodic, high-frequency signals'. Now, as reported on pages 42 and 44 of this issue, all three types of signal have been detected from a single neutron-star binary, known as SAX 11808.4-3658. The observations point to the rate of rotation of the neutron star as a critical factor in the generation of these signals.