A neutron star is the crushed core of a massive star that ran out of fuel, collapsed under its own weight, and exploded as a supernova. A neutron star can spin as fast as 43,000 times per minute and boast a magnetic field a trillion times stronger than Earth's. Matter within a neutron star is so dense a teaspoonful would weigh about a billion tons on Earth.
Observations of X-ray pulses from 1E 2259+586 from July 2011 through mid-April 2012 indicated the magnetar's rotation was gradually slowing from once every seven seconds, or about eight revolutions per minute. On April 28, 2012, data showed the spin rate had decreased abruptly, by 2.2 millionths of a second, and the magnetar was spinning down at a faster rate.
Astronomers dubbed the event an "anti-glitch," said co-author Neil Gehrels, principal investigator of the Swift mission at NASA's Goddard Space Flight Center in Greenbelt, Md. "It affected the magnetar in exactly the opposite manner of every other clearly identified glitch seen in neutron stars."
The discovery has important implications for understanding the extreme physical conditions present within neutron stars, where matter becomes squeezed to densities several times greater than an atomic nucleus. No laboratory on Earth can duplicate these conditions.
A report on the findings appears in the May 30 edition of the journal Nature.
Processes that lead to a sudden rotational slowdown constitute a new theoretical challenge.
On April 21, 2012, just a week before Swift observed the anti-glitch, 1E 2259+586 produced a brief, but intense X-ray burst detected by the Gamma-ray Burst Monitor aboard NASA's Fermi Gamma-ray Space Telescope. The scientists think this 36-millisecond eruption of high-energy light likely signaled the changes that drove the magnetar's slowdown.
"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," said lead author Robert Archibald, a graduate student at McGill.
Goddard manages Swift, which was launched in November 2004. The telescope is operated in collaboration with Pennsylvania State University in University Park, Pa., the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Va. International collaborators are in the United Kingdom and Italy, and the mission includes contributions from Germany and Japan.
› Download additional graphics from NASA Goddard's Scientific Visualization Studio
› Penn State press release
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› "Eclipsing Pulsar Promises Clues to Crushed Matter" (08.17.10)
› The McGill Pulsar Group's Magnetar Catalog
› NASA's Swift mission
› NASA's Fermi Gamma-ray Space Telescope
NASA's Goddard Space Flight Center, Greenbelt, Md.