William Atkins
Friday, 22 May 2009 19:35
Science -
Space
Page 2 of 3
The CSIRO article states,
“The material from the companion would form a flat, spinning ‘accretion disk’ around the neutron star, blocking the pulsar’s radio waves. As the flow of material from the companion decreased and then stopped, the radio waves would reappear, and the object could be recognised as a pulsar.”
However, astronomers have never before found an accretion disk around a millisecond pulsar. Anne Archibald, one of the lead researchers, states,
“No other millisecond pulsar has ever shown evidence of an accretion disk.” [CSIRO]
However, they found an accretion disk (as early as 2001) around this one, called PSR J1023+0038, but it disappeared over time. Its companion star is a 17th-magnitude star.
They conclude, from their research, that material from a companion star is not always necessary to form a millisecond pulsar.
In fact, the researchers state in the abstract to their paper,
“Radio pulsars with millisecond spin periods are thought to have been spun up by transfer of matter and angular momentum from a low-mass companion star during an x-ray-emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have been detected.”
“Here, we report on detection and follow-up observations of a nearby radio millisecond pulsar (MSP) in a circular binary orbit with an optically identified companion star. Optical observations indicate that an accretion disk was present in this system within the last decade. Our optical data show no evidence that one exists today, suggesting that the radio MSP has turned on after a recent LMXB phase.”
Astronomers observe pulsars by the radio wave radiation they emit as the pulsar rotates. Scientists often compare its radio wave signal to a beam of light coming from a lighthouse, as seen on Earth.
Page three concludes....
