LANL scientists seek magnetars' secrets

Sue Vorenberg | The New Mexican

3/6/2009 - 3/5/09

You might not think you have anything in common with the supermassive, high-power magnetic star remnants that astrophysicists call magnetars.

But when it comes to aging, we all might slow down in a similar way — with declining bursts of energy and exhaustion washing over us until we finally peter out.

David Palmer, a Los Alamos scientist, is coming to that conclusion after taking a closer look at magnetars through NASA's Swift satellite, which detects and investigates X-ray and gamma ray bursts through software that Palmer helped develop.

Recently, the satellite detected two types of magnetars in the same place, indicating that they actually could be the same thing, just at different stages of life, he said, adding that the notion was something of a surprise.

"It's like learning the giant beasts who leap out of the ocean and splash down on the surface are the same as the ones you have heard singing in the depths," Palmer said of the discovery.

Magnetars are a subcategory of neutron stars, which are extremely dense remnants of exploded suns.

To get an idea of how dense neutron stars are, imagine compressing all the material in our sun into a 12-mile radius object.

In magnetars, the forces of those ultra-dense stars are even more mangled and strange.

Magnetars spin — much like the Earth does over the course of a day — but they do a complete rotation in a matter of seconds, or less.

And magnetars have the most intense magnetic fields of anything in the universe.

"To get an idea of how strong those fields are, if you were 1,000 miles away, they could rip the iron from your blood," Palmer said, pausing briefly.

"These things are best studied from a distance," he added.

Scientists can see these stars by looking at bursts of magnetic radiation emitted from the weird and chaotic forces inside them.

The mechanisms behind all the magnetic weirdness inside those stars, though, are poorly understood, Palmer said.

The discovery that two types of magnetars could actually be different life stages of a single one could help scientists understand those mechanisms better.

Before taking a closer look with Swift, scientists knew that a type of magnetar called an anomalous X-ray pulsar lived in the constellation Norma, which is about 30,000 light years from Earth.

On Jan. 22, the Swift satellite detected another type of X-ray burst coming from the same place, indicating it could be a different type of magnetar, called a soft gamma repeater.

Both types of object burst somewhat erratically — with lots of activity followed by periods of quiet.

But soft gamma repeaters tend to burst more slowly than anomalous X-ray pulsars, which could mean that the soft gamma repeaters are older than the anomalous X-ray pulsars, Palmer said.

"Seeing both types in the same place indicates this could be a transition state," he said. "And as these objects get older, they tend to slow down."

But while the idea appears to make sense logically, there's still a lot of processes at play in magnetars that we don't understand, and more work needs to be done before making any real conclusions, said Chryssa Kouveliotou, an astrophysicist at NASA's Marshall Spaceflight Center.

"Right now we're just trying to understand the physical mechanisms that produce these bursts," Kouveliotou said. "I can't determine if there's an evolutionary sequence that takes place from one part of life to another."

Bursts could be caused by quakes on a magnetar's surface and also by the strange interplay of gravity and the magnetic field, but scientists aren't sure exactly what's going on with those processes yet, which is why data from Swift is important, Palmer said.

It appears that the spin, density and other aspects of magnetars actually trap the magnetic field in the star so it can only escape in bursts, he said.

"We think as the magnetic field leaks out, it sort of leaks out in tangles," Palmer said. "And these tangles have a lot of energy. Magnetic fields want to be untangled. And that might be why we see these patterns."

In the world of astrophysics, magnetars are somewhat rare and hard to come by. The soft gamma repeater in the constellation Norma was only the sixth one ever detected. And overall only a little more than a dozen magnetars have been classified.

The objects have relatively short life-spans, at least from a planetary science perspective — lasting only somewhere between 10,000 and 30,000 years.

That short lifespan makes them hard to detect, but it also indicates that there could be many more out there. And considering that the recent X-ray burst was strong enough to give an astronaut in Earth orbit a radiation dose similar to that of a dental X-ray, at 30,000 light years away — understanding more about them could have broader implications for us as a species or as a planet, Palmer said.

"These things are extremely violent, and we don't really understand magnetic fields all that well," Palmer said. "Detecting these processes with Swift gives us some very valuable data."

Contact Sue Vorenberg at svorenberg@sfnewmexican.com.