Why Do Pulsars Spin?

A new theory reveals that the spin is induced by the super nova explosion

 
Pulsars are rapidly rotating neutron stars that emit detectable electromagnetic radiation.

They emerge after supernova explosions, which take place when a massive star dies and explodes.

What is left is compressed into a dense, rapidly spinning pulsar. "Picture something about the mass of the sun being pushed down to the size of a small American city, like Raleigh," said Dr. John Blondin, professor of physics in North Carolina State University's College of Physical and Mathematical Sciences. "We've known about pulsars since the 1960s. We can determine how fast they're spinning by how rapidly they pulse. It's like a searchlight on a lighthouse - each time the pulsar spins, and emits a radio pulse directed toward earth, we pick up on it. The period between the pulses tells us how fast it's spinning." explained Blondin. More precisely, this can reach more than 20 rotations per second.

Astronomers have believed that the spin was provoked by the conservation of angular momentum before the occurrence of the super nova explosion. "Think about figure skaters. They start a spin with their arms and legs farther out from the body, and increase their rotation speed when they pull their limbs in more tightly. That's what the conservation of angular momentum is - the idea that if you take a large object with a slight rotation and compress it down, the rotation speed will increase", said Blondin.

But this is a hazardous idea, as researchers cannot say if the stars before the super nova were even spinning.

That's why Blondin's team made a computer model of a supernova explosion using the new Cray X1E supercomputer at the National Center for Computational Sciences, the only computer with enough processing power able to realize a three-dimensional model of a pulsar's creation.

The results disagree with any previous model, revealing that a pulsar's spin doesn't have any link with an eventual spinning of the progenitor star; the spin is the result of the super nova explosion itself.

"We modeled the shockwave, which starts deep inside the core of the star and then moves outward. We discovered that as the shockwave gains both the momentum and the energy needed to blow outward and create the explosion, it starts spiraling all on its own, which starts the neutron star at the center of the star spinning in the opposite direction. None of the previous two-dimensional modeling of supernova explosions had picked up on this phenomena", said Blondin.

"Supernova explosions produce many of the heavy elements found on the periodic chart, like gold. Understanding these explosions can help us to better understand our own planet and solar system", he added.

Image credit: North Carolina University

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By    26 Feb 2007, 10:28 GMT