X-ray Pulsar — This dramatic artist’s vision shows a city-sized neutron star centered in a disk of hot plasma drawn from its enfeebled red companion star.
Ravenously accreting material from the disk, the neutron star spins faster and faster emitting powerful particle beams and pulses of X-rays as it rotates 400 times a second. Could such a bizarre and inhospitable star system really exist in our Universe?
Based on data from the orbiting Rossi X-Ray Timing Explorer (RXTE) satellite, research teams have recently announced a discovery which fits this exotic scenario well – a “millisecond” X-ray pulsar.
The newly detected celestial X-ray beacon has the unassuming catalog designation of SAX J1808.4-3658 and is located a comforting 12,000 light years away in the constellation Sagittarius.
Its X-ray pulses offer evidence of rapid, accretion powered rotation and provide a much sought after connection between known types of radio and X-ray pulsars and the evolution and ultimate demise of binary star systems.
Pulsars are rotating neutron stars with strong magnetic fields (about 1011 to 1012 Gauss, similar to magnetars, but with weaker magnetic fields), formed when a large star goes supernova and compresses its core as it blows off its outer layers, or when a white dwarf accretes enough material to force gravitational collapse.
The pulsating nature comes from the rapid rotation of the neutron star whose magnetic field axis is not aligned with its spin axis. As material is funneled onto the magnetic poles of the star, energy from this accreted matter is released in the form of X-rays.
The concentration of emitted X-rays from the magnetic poles appears to a distant observer as a periodic change in the intensity of the source, like a lighthouse.