NASA - National Aeronautics and Space Administration

This artist rendering depicts how a magnetar might appear if we could travel to one and view it up close, something that would not be advisable. Credit: Sky & Telescope, Gregg Dinderman.
> Click here for larger image
There’s a lot of strange stuff in outer space. But of all the bizarre objects out there, one of the weirdest would be a neutron star. These objects form when the core of a huge star stops producing energy. Gravity collapses the core to form a neutron star. The rest of the star blows up in a stupendously powerful explosion called a supernova.

Neutron stars are unlike anything found on Earth. These objects pack about one to two Suns worth of material into a ball no larger than New York City. A few cups of neutron star stuff would outweigh Mount Everest, the highest mountain on Earth!

For years, astronomers have known that some neutron stars emit regular pulses. They essentially go beep-beep-beep-beep-beep, and so on, with a perfectly regular spacing between each beep. These neutron stars are known as pulsars, for their pulsing signals. Pulsars spin very rapidly, and it’s this rapid spin that provides the energy for their pulses.

In the 1990s, astronomers discovered a different kind of neutron star. These objects spin slower than pulsars. Because they spin slower, they must be drawing most of their energy from a different kind of source. This source is magnetism. Magnetars are the most magnetic known objects in the entire universe! Their magnetic fields are so powerful that they could kill a human being many thousands of miles away.

This Chandra image shows the supernova Kes 75. The pulsar is in the center of the blue area at the top. Credit: NASA/CXC/M. Gonzalez/F. Gavriil/P. Slane
> Click for larger image.
> Click for high resolution TIF image Until now, pulsars and magnetars seemed to form two separate classes. A neutron star was either a pulsar or a magnetar, but not both. But using NASA’s Rossi X-ray Timing Explorer (RXTE), astronomers have found a neutron star that seems to share characteristics of both types.

This neutron star is known as PSR J1846-0258. “PSR” is short for “pulsar,” and the numbers stand for its sky location in the constellation Aquila. For years, PSR J1846 seemed like an ordinary pulsar, beeping three times per second as it spins on its axis.

But a team of Canadian and American astronomers led by Fotis Gavriil of NASA’s Goddard Space Flight Center in Greenbelt, Md., decided to take a closer look at this pulsar. They realized that RXTE observed this pulsar in 2006, but nobody had looked at the observations in detail. When Gavriil and his colleagues studied these observations, they realized that PSR J1846 gave off five huge outbursts of energy. Four of these bursts occurred on May 31, 2006, and the other on July 27, 2006. Each of these flares lasted less than one second, yet they unleashed the energy of tens of thousands of Suns!

These images from NASA's Chandra X-ray Observatory show the pulsar in Kes 75 in October 2000 (left) and June 2006 (right). The pulsar clearly brightened in X-rays after giving off powerful outbursts earlier in 2006. Credit: NASA/CXC/M. Gonzalez/F. Gavriil/P. Slane.
> Click for larger image. Regular pulsars have never been seen to produce such violent bursts of energy. But magnetars generate them frequently. So Gavriil and his team have found a pulsar that produces outbursts like those generated by magnetars. "We are watching one type of neutron star literally change into another right before our very eyes. This is a long-sought missing link between different types of pulsars," says Gavriil.

"Young, fast-spinning pulsars were not thought to have enough magnetic energy to generate such powerful bursts," says team member Marjorie Gonzalez, who is now based at the University of British Columbia in Vancouver, Canada. "Here’s a normal pulsar that’s acting like a magnetar."

Astronomers know that PSR J1846 is very young. It is no more than 884 years old, which is very young compared to most objects in the universe. Astronomers used to think that a neutron star was either a magnetar or a pulsar. But this discovery suggests that maybe magnetars are just a phase of a neutron star’s life cycle. In other words, maybe a neutron star starts off as a magnetar, but that it doesn’t start producing outbursts until its several hundred years old. It acts like a magnetar for perhaps a few thousand years, and then it settles down and becomes a pulsar.

Robert Naeye
Goddard Space Flight Center