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Contact: Erica Rolfe
European Space Agency

Cannibal star eats companion

Artist's impression of a pulsar 'eating' a companion star
Click here for a high resolution photograph.

ESA’s Integral space observatory has made its first discovery of a fast-spinning star that is swallowing its smaller neighbour.

The star in a spin is no ordinary star. Originally at least eight times more massive than the Sun, it has collapsed to a superdense neutron star only 20 km across. One teaspoonful of its material would weigh about a billion tonnes. Although it is far too small to be seen with an ordinary telescope, the neutron star can be seen in X-ray light. It was found by Integral during a routine scan of the sky on 2 December 2004, when it suddenly gave off a powerful X-ray flare.

Measurements by Integral and NASA’s Rossi X-ray Timing Explorer spacecraft show that the cannibal star is a ‘pulsar’ – a rapidly rotating neutron star. In fact, it is one of the fastest spinning pulsars ever found. At present it is rotating at a dizzying speed - about 600 times every second – and gradually getting even faster. The spin-up process occurs when gas ripped from the companion crashes onto the surface. This feeding frenzy heats it to a temperature of almost a billion degrees, releasing huge amounts of X-rays and gamma rays.

Meanwhile, the companion has already shrunk to a fraction the size of our Sun, perhaps as small as 40 Jupiter masses. Both stars are so close that they would fit into the radius of the Sun. In order to survive, the shrinking neighbour zooms around its neutron star neighbour in just 2.5 hours.