'Lazy' pulsar orbits a faster and more energetic companion in binary system

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Paris, June 24 : Astronomers have spotted an extremely rare sight of two pulsars orbiting each other in a binary system, in which a slowly-rotating 'lazy' pulsar or neutron star (Pulsar B) orbits a faster and more energetic companion (Pulsar A).

This is the first time that signals from both stars of a binary pulsar system has been detected, thanks to the XMM-Newton.

Each star of the closely-packed system is a dense neutron star, spinning extremely fast, radiating X-rays in pulses, and is the fast-rotating, dead heart of a once-massive star.

"These stars are so dense that one cup of neutron star-stuff would outweigh Mt. Everest," said Alberto Pellizzoni, lead author of the article where the results are reported. "Add to that the fact that the two stars are orbiting really close to each other, separated by only 3 light-seconds, about three times the distance between Earth and the Moon," he added.

XMM-Newton discovered X-ray emission from both pulsars in October 2006.

What Pellizzoni's team saw could not be explained by the workings of pulsar A alone, which was known to be the only significant power plant in the system.

Besides, the X-ray pulses detected from pulsar B were too strong. The energy that it lost by rotation could not account for all the X-ray radiation observed.

The theory that the observed X-rays might originate from residual internal heat of this 50 million year-old pulsar was also ruled out.

Pulsar B is an oddity, in that it is very different from a 'normal' pulsar.

"One possible solution for the mystery could be mutual interaction between the two stars, where the lazy star derives energy from the other," said Pellizzoni.

Pulsar B's X-ray emission might be visible because pulsar A's wind intercepts the magnetosphere of pulsar B, powering pulsar B's wind and heating up the neutron star's surface.

Though the fundamental physical processes involved in these extreme interactions are a matter of debate among theoretical physicists, but with XMM-Newton's observations, scientists have gained new insight, providing a new experimental setting for them.

In X-rays, it will be possible to study the subsurface and magnetospheres of the stars as well as the interaction between the two in that close, heated environment.

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