Slowing spin of distant neutron star puzzles astronomers

Astronomers say a NASA space telescope has observed a spinning neutron star suddenly slowing down, offering clues to understanding such extremely dense objects. A neutron star is what is left after a massive star runs out of fuel, collapses under its own weight and explodes as a supernova. Neutron star 1E 2259+586 is located about 10,000 light-years from Earth and is one of about two dozen neutron stars called magnetars, possessing very powerful magnetic fields and occasionally producing high-energy explosions or pulses. Observations by NASA's Swift X-ray telescope of pulses from July 2011 through mid-April 2012 indicated the magnetar's rotation was gradually slowing from once every 7 seconds, or about eight revolutions per minute. On April 28, 2012, data showed the spin rate had decreased abruptly and the magnetar was slowing down at a faster rate, the space agency reported Wednesday. "Astronomers have witnessed hundreds of events, called glitches, associated with sudden increases in the spin of neutron stars, but this sudden spin-down caught us off guard," Victoria Kaspi, a professor of physics at McGill University in Montreal, said. Kaspi heads a team that uses Swift to routinely monitor magnetars. Astronomers have dubbed the unexpected event an "anti-glitch." "It affected the magnetar in exactly the opposite manner of every other clearly identified glitch seen in neutron stars," Neil Gehrels, principal investigator of the Swift mission at NASA's Goddard Space Flight Center in Greenbelt, Md., said. Just a week before Swift observed the anti-glitch, 1E 2259+586 produced a brief but intense X-ray burst, an eruption of high-energy light scientists say they believe possibly was a symptom of the changes that drove the magnetar's slowdown. Processes that lead to a sudden rotational slowdown constitute a new theoretical challenge, the researchers said. "What is really remarkable about this event is the combination of the magnetar's abrupt slowdown, the X-ray outburst, and the fact we now observe the star spinning down at a faster rate than before," lead author Robert Archibald, a graduate student at McGill, said.