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Jekyll-Hyde neutron star discovered by researchers

February 22, 2008

Like something out of a Robert Louis Stevenson novel, researchers at NASA and McGill University discovered an otherwise normal pulsar which violently transformed itself temporarily into a magnetar, a stellar metamorphosis never observed before.

Powerful X-ray bursts from the pulsar in the Kes 75 supernova remnant were discovered by former McGill PhD Dr. Fotis Gavrill, currently assigned to NASA's Goddard Space Flight Center in Greenbelt, Maryland, in collaboration with Dr. Victoria Kaspi, leader of the McGill University Pulsar Group, her graduate student Maggie Livingstone, and very recent McGill PhD, Dr. Majorie Gonzalez, now of the University of British Columbia. Their results were published February 21 in the journal Science.

Pulsars and magnetars belong to the same class of ultradense, small stellar objects called neutron stars, left behind after massive stars die and explode as supernovae. Pulsars, by far the most common type, spin extremely rapidly and emit powerful bursts of radio waves. These waves are so regular that, when they were first detected in the 1960's, researchers considered the possibility that they were signals from an extraterrestrial civilization. By contrast, magnetars are slowly rotating neutron stars which derive their energy from incredibly powerful magnetic fields, the strongest known in the universe. There are over 1800 known pulsars in our galaxy alone, but magnetars are much less common, said the researchers.

"Magnetars are actually very exotic objects," said Dr. Kaspi, McGill's Lorne Trottier Chair in Astrophysics and Cosmology and Canada Research Chair in Observational Astrophysics. "Their existence has only been established in the last 10 years, and we know of only a handful in the whole galaxy. They have dramatic X-ray and gamma-ray bursts and can emit huge flares, sometimes brighter than all other cosmic X-ray sources in the sky combined."

This discovery, based on data from NASA's Rossi X-ray Timing Explorer (RXTE) and Chandra X-ray Observatory satellites, is the long-sought-after missing link between the two types of neutron star, said the researchers. To date, the evolutionary relationship between pulsars and magnetars has been poorly understood. It was not clear if magnetars are simply a rare class of pulsars, or if some or all pulsars go through a magnetar phase as a normal part of their life cycles.

"Researchers have long been looking for transition objects," explained Maggie Livingstone. "In particular we've kept our eyes on pulsars with high magnetic fields."

"This source could be evolving into a magnetar," added Dr. Kaspi. "Or it could just show occasional magnetar-like properties, we just don't know yet. We're very anxious to find out."

McGill University