An experiment here on Earth has simulated one of the most extreme optical processes in the microcosm.
Physicists at Princeton’s Plasma Physics Laboratory (PPPL) have succeeded in creating collimated jets that resemble those coming from baby stars and feeding black holes.
Our laboratory version is nowhere near as large or powerful as those in space, which can continue for millions of light years. But the results have revealed for the first time a long-hypothesized plasma instability that could help us understand how these explosions occur and fly through space at near-light speeds.
“These experiments show that magnetic fields are very important for the formation of plasma jets,” says PPPL physicist Will Fox. “Now that we can have an understanding of what makes these jets, we can, in theory, study the massive jets of space and learn something about black holes.”
Interstellar jets are something of a mystery. They are long, thin streams of plasma that shoot from the poles of certain cosmic objects along the axis of rotation.
In black holes, they form when the black hole feeds; scientists believe that some of the material surrounding the black hole is deflected and accelerated along magnetic lines to the poles, where they are launched using jets.
A similar mechanism is thought to work with baby stars, which feed off material in a similar fashion. But we really don’t know the details of jet formation, which is a huge gap in our understanding of atmospheric processes.
Led by PPPL physicist Sophia Malko, the research team has now identified one possible mechanism.
The team wanted to study the interaction between magnetic fields and plasma, which is a state of matter composed of ionized particles. To do this, they used a technique known as proton radiometry, which used the deflection of positively charged subatomic particles to plot patterns in the plasma’s magnetic field.
The plasma was created by firing a laser at a thin plastic disk. At the same time a mixture of protons and X-rays was created by firing a laser at a capsule of hydrogen and helium that underwent nuclear reactions during heating.
Protons and X-rays passed through a nickel mesh that was sandwiched between two strong magnetic coils. Acting like a paste, the holes forced the light and particles to form a grid of tiny rays.
Distorted by the electromagnetic interaction of the plasma itself and the external magnetic field, the proton beams were used as a measure of internal chaos.. Since the X-rays passed through unobstructed and undistorted, it provided a point of comparison for the behavior of protons.
What the team saw was a magnetic field pulsing outward under the pressure of the expanding plasma. As the plasma water continued to enter the magnetic field, bubbling and foaming began to appear at the edges, like mushroom and pillar-like shapes – just as cold milk blooms when you drop it into hot coffee.
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“During the interaction, multiple structures form where the field meets the plasma because there are large differences in temperature, density and magnetic field strength,” Malko explains. “It’s a great place for them to grow up.”
Eventually, as the plasma ran out of energy, the magnetic field returned to space – which caused the plasma to flow in long, narrow, enhanced jets – like those that erupt from black holes.
The bubbling and foaming at the edges of the plasma was a particularly interesting feature, the researchers say – a phenomenon known as magneto-Rayleigh-Taylor instability, a type of instability known in fluid dynamics, and the difference if the involvement of the magnetic field. .
“When we did the experiments and analyzed the data, we realized we had something big,” Malko says.
“Observing the magneto-Rayleigh Taylor instability resulting from the interaction of a plasma with a magnetic field has long been thought to occur but has never been directly observed until now. This observation helps to confirm that instability occurs when expanding plasma meets magnetic fields. We did not so, know that our investigation would have that kind of accuracy!
Observations do not only have implications for astrology. Plasmas with magnetic fields form the basis of a type of fusion reactor that physicists hope could one day produce efficient and clean energy.
Keeping the plasma inside the magnetic field is a bit of a challenge; knowing more about how plasma and magnetic fields interact gives us more information to use in future problem solving.
“Now that we have measured this instability very precisely, we have the information we need to improve our models and potentially simulate and understand spaceflight at a higher level than ever before,” Malko says. “It’s exciting that humans can make something in the lab that normally exists in space.”
The research is published in Physical Review Research.
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