Monday, February 26, 2007

Pulsar's creation.

Volume rendering of 3-D simulation of a pulsar's formation. Credit: Image courtesy of North Carolina State University

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.

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.”

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

Latest Spin on Neutron Stars from Louise Riofrio
Scientist Discovers New Explanation For Pulsar's Spin from Science Daily

Sunlight heats ice on surface of comet McNaught

The unique images reveal three clear jets of gas, which are seen to spiral away from the nucleus as it rotates, like a Catherine Wheel firework.

"These jets are produced when sunlight heats ices on the surface of the comet, causing them to evaporate into space and create 'geyser' like jets of gas and small dust particles, which stretch over 13,000 km into space - greater than the diameter of the Earth - despite the fact that the nucleus of the comet is probably less than 25 km in diameter,"

By comparing images like this taken at different times, astronomers should be able to calculate how fast the nucleus rotates from the changing pattern of jets.

Other images also reveal that while the gas forms spiral jets, the large dust particles released from the comet follow a different pattern, as they are thrown off the comet's surface on the brightly lit side towards the Sun, producing a bright fan, which is then blown back by the pressure of sunlight itself.

Unique Observations Of Comet McNaught Reveal Sprinkling Nucleus
Comet McNaught. Image courtesy of European Southern Observatory

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