Artist's conception of J1023 during its active phase, in which matter overflowing from the companion formed a bright accretion disk. Flickering occurs as knots of hot material form and disperse in the turbulent disk. Image produced by using the software BinSim and estimated parameters of the J1023 system.
Credit: Anne Archibald
Observations taken in 2007 with the U.S. National Science Foundation's Green Bank Telescope (GBT) in West Virginia finally showed that the object has become a millisecond pulsar, spinning an astounding 592 times per second.
"No other millisecond pulsar has ever shown evidence for an accretion
disk," said Archibald. "We know that another type of binary-star system, called a low-mass X-ray binary (LMXB), also contains a fast-spinning neutron star and an accretion disk, but these don't emit radio waves."
Experts thought that LMXBs were probably stars in the process of getting spun up, and that they would later emit radio waves as a pulsar – but before now there was no proof. "This object appears to be the 'missing link' connecting the two types of systems," said Archibald.
Cosmic laboratory
"It appears this thing has flipped from looking like an LMXB to looking like a pulsar, as it experienced an episode during which material pulled from the companion star formed an accretion disk around the neutron star. Later, that mass transfer stopped, the disk disappeared, and the pulsar emerged," said Scott Ransom of the NRAO.
The scientists have now studied J1023 in detail, and their results indicate that the neutron star's companion has less than half the Sun's mass, and orbits it once every four hours and 45 minutes. "This system gives us an unparalleled 'cosmic laboratory' for studying how millisecond pulsars evolve," said Stairs.
Co-author Maura McLaughlin, of West Virginia University, agrees: "Future observations of this system at radio and other wavelengths are sure to hold many surprises."
With the U.S. National Science Foundation and the National Radio Astronomy Observatory.
