”Burping” astrophysical jets recreated by plasma experiment

February 21st, 2009 - 2:38 pm ICT by ANI  

London, Feb 21 (ANI): A plasma experiment by scientists has recreated jets of charged particles for the first time in a laboratory, which could shed light on the behaviour of ”burping” astrophysical jets from stars and galaxies.
Astrophysical jets are among the largest and most energetic objects in the universe.
The matter inside them travels at nearly the speed of light from colossal black holes at the centres of galaxies. Smaller jets spew at lower speeds from young stars surrounded by discs of gas and dust.
Theorists don”t know exactly how jets form, but they believe the particles inside them are accelerated by magnetic fields, which could be whipped up as matter rotates around a star or black hole.
But, the magnetic fields that seem to keep jets focused can also form kinks that can destabilize the beams, raising questions about how the jets can remain tightly focused over very long distances.
Jets are also clumpy and seem to throw out material in bursts.
“They”re very inhomogeneous with lots of blobs, and it’’s very clear that the jet turns on and off,” said Eric Blackman, an astrophysicist at the University of Rochester.
The source of this episodic behaviour is not clear.
But now, according to a report in New Scientist, Blackman and colleagues, led by plasma physicist Andrea Ciardi of the Ecole Normal Superieure in Paris, have recreated the intermittent behaviour that seems to create the clumps seen in telescopes.
“This is the first time we can actually produce episodic behaviour. The experiment shows jets can propagate very far, but they can be quite unstable at the source,” Ciardi told New Scientist. To create a sequence of bursts, Andrea Ciardi and colleagues fed more than 100 billion watts of power into electrodes connected by a sheet of aluminium foil.
The current created a coiled magnetic field above the foil. It also burned a hole in the foil, turning the aluminium into a soup of charged particles called a plasma.
Because charged particles are accelerated in the presence of a magnetic field, the plasma then sped through the magnetic loop at hundreds of kilometres per second - comparable to speeds seen in stellar jets.
As the first jet was propelled away, more aluminum plasma that had burned off the foil moved in to take its place, and a new jet formed.
The team found that the magnetic environment left over from previous jets seems to stabilize and focus the next jet.
The flows that can be modelled by computer tend to be slow and cool.
Pudritz notes that experiments like this one can get a bit closer to simulating extreme astrophysical conditions, where it is not possible to measure the configuration of magnetic fields. (ANI)

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