Jets of charged particles have been created in successive bursts for the first time in the laboratory. The work could shed light on the behaviour of 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鈥檛 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.
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But the magnetic fields that seem to keep jets focused can also form kinks that can destabilise the beams, raising questions about how the jets can remain tightly focused over very long distances.
鈥楲ots of blobs鈥�
Jets are also clumpy and seem to throw out material in bursts. 鈥淭hey鈥檙e very inhomogeneous with lots of blobs, and it鈥檚 very clear that the jet turns on and off,鈥� says Eric Blackman, an astrophysicist at the University of Rochester.
The source of this episodic behaviour is not clear. The material that feeds jets might not flow smoothly from discs, instead falling in clumps. Or the disc might help wind up magnetic fields surrounding a star, building up pressure in the fields that eventually creates intermittent bursts.
Computer models can鈥檛 fully simulate these conditions. But 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.
鈥淭his is the first time we can actually produce episodic behaviour,鈥� Ciardi told 快猫短视频. 鈥淭he experiment shows jets can propagate very far, but they can be quite unstable at the source.鈥�
Particle soup
Several teams have managed to create single jets in the laboratory.
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 鈥� comparable to speeds seen in stellar jets.
As the first jet was propelled away, more aluminium 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 stabilise and focus the next jet.
鈥楨xtreme conditions鈥�
鈥淚t think it鈥檚 a very important piece of work,鈥� says of McMaster University in Hamilton, Ontario, who performs computer simulations of jet formation but was not involved in this study.
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.
鈥淚t opens the door to explore a lot of really exotic behaviour,鈥� he told 快猫短视频.
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