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North Carolina State U. Scientist Discovers New Explanation forPulsar's Spin (Forwarded)



 
 
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Old January 4th 07, 04:12 PM posted to sci.astro
Andrew Yee
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Default North Carolina State U. Scientist Discovers New Explanation forPulsar's Spin (Forwarded)

News Services
North Carolina State University

Media Contacts:
Dr. John Blondin, 919/515-7096
Tracey Peake, News Services, 919/515-6142

FOR IMMEDIATE RELEASE: Jan. 3, 2007

NC State Scientist Discovers New Explanation for Pulsar's Spin

A researcher at North Carolina State University has developed a
three-dimensional computer model that shows how pulsars obtain their spin,
which could lead to a greater understanding of the processes that occur
when stars die.

Dr. John Blondin, professor of physics in NC State's College of Physical
and Mathematical Sciences, along with colleague Anthony Mezzacappa at the
Oak Ridge National Laboratory, used the CRAY X1E supercomputer to develop
a three-dimensional model of a pulsar's creation, and in the process
discovered that conventional wisdom concerning the formation of these
celestial objects wasn't correct.

Their findings are published in the Jan. 4 edition of the journal Nature.

Pulsars are rapidly rotating neutron stars formed in supernova explosions,
which occur when a massive star reaches the end of its life and explodes.
The remaining matter is compressed into a dense, rapidly spinning mass --
a neutron star, or pulsar -- so-called because scientists first discovered
them due to their regularly timed radio emissions.

"Picture something about the mass of the sun being pushed down to the size
of a small American city, like Raleigh," Blondin says. "That's what
happens when a neutron star is formed.

"We've known about pulsars since the 1960s," Blondin continues. "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."

Pulsars spin very rapidly -- 20 or more times per second. Scientists have
assumed that the spin was caused by the conservation of angular momentum
from a star that was spinning before it exploded.

"Think about figure skaters," Blondin says. "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."

However, scientists had no idea if the stars that were producing the
pulsars were even spinning to begin with. Blondin and his colleague
decided to create 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 to accomplish the task. The
resultant model demonstrated that a pulsar's spin doesn't have anything to
do with whether or not the star that created it was spinning; instead, the
spin is created by the explosion itself.

"We modeled the shockwave, which starts deep inside the core of the star
and then moves outward," Blondin says. "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."

Blondin hopes that this new information about the creation of pulsars will
lead to a greater understanding of supernova explosions. "Supernova
explosions produce many of the heavy elements found on the periodic chart,
like gold," he says. "Understanding these explosions can help us to better
understand our own planet and solar system."

IMAGE CAPTION:
[http://news.ncsu.edu/releases/2007/j...rformation.htm (72KB)]
Volume rendering of 3-D simulation of a pulsar's formation.


 




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