Magnetic forces shape cosmic jets streaming out of stars

February 11th, 2009 - 4:21 pm ICT by IANS  

Washington, Feb 11 (IANS) Jets of matter streaming out of stars are among the most striking cosmic phenomena, but astrophysicists were unable to explain how they achieve varied shapes. “The predominant theory says that jets are essentially fire hoses that shoot out matter in a steady stream, and the stream breaks up as it collides with gas and dust in space - but that doesn’t appear to be so after all,” said Adam Frank, professor of astrophysics at the University of Rochester and co-author of the paper.

“These experiments are part of an unusual international collaboration of plasma physicists, astronomers and computational scientists. It’s a whole new way of doing astrophysics. The experiments strongly suggest that the jets are fired out more like bullets or buckshot. They don’t break into pieces - they are formed in pieces.”

Frank said the experiment, conducted by Sergey Lebedev’s team at the department of physics, Imperial College London, may be the best astrophysical experiment that’s ever been done.

Replicating the physics of a star in a lab is exceptionally difficult, he said, but the Imperial experiment matches the known physics of stellar jets surprisingly well.

At Imperial, Lebedev sent a high-powered pulse of energy into an aluminium disk. In less than a few billionths of a second, the aluminium began to evaporate, creating a cloud of plasma very similar to the plasma cloud surrounding a young star.

Where the energy flowed into the centre of the disk, the aluminium eroded completely, creating a hole through which a magnetic field from beneath the disk could penetrate.

The field initially pushes aside the plasma, forming a bubble within it, said Frank, who carried out the astrophysical analysis of the experiment. As the field penetrates further and the bubble grows, however, the magnetic fields begin to warp and twist, creating a knot in the jet, said a Rochester release.

These findings were published in the current issue of Astrophysical Review Letters.

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