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XMM-Newton has, for the first time, detected X-ray pulses emanating from both stars of a closely packed binary pulsar system, revealing two extremely dense rapidly rotating neutron stars. Pulsars are highly magnetic neutron stars, the dead hearts of once massive stars. Observing two pulsars orbiting each other is a rare treat, but now these two dead stars are bathed in fresh light thanks to the probing X-ray observations made by the XMM-Newton space telescope.
Animation of the double pulsar system. Credit: John Rowe Animations. Pulsar system PSR J0737-3039 contains one slowly rotating ‘lazy’ neutron star – referred to by the research team as pulsar B – orbiting a faster and more energetic companion star (pulsar A). The pair of stars are separated by just three light seconds, about three times the distance between the Earth and the Moon. The new X-ray observations raised some intriguing physical problems: the emission signals could not be explained by the workings of pulsar A alone, which was known to be the only significant power plant in the system. The X-ray pulses from pulsar B were just too strong to match the observed emission and the energy that is lost by the rapid rotation of the pair could not account for all the X-ray radiation observed either. "One possible solution for the mystery could be mutual interaction between the two stars, where the lazy star derives energy from the other," says Albert Pellizzoni, lead author of the results, which are published in the May 2008 edition of the Astrophysical Journal. This means that pulsar B’s X-ray emission might only be visible because pulsar A's wind intercepts the magnetosphere of the lazy pulsar, powering its wind and heating up the neutron star's surface.
Artist impression of the XMM-Newton space telescope. Image: ESA (C. Carreau). The fundamental physical processes involved in these extreme interactions are a matter of some debate among theoretical physicists, but with XMM-Newton's unrivaled observations, scientists have been offered a novel experimental setting to study the subsurface and magnetospheres of the stars, as well as the interaction between the two in such a close, heated environment, the results of which will undoubtedly push the boundaries of scientific knowledge to new levels.
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