NASA image of a supernova remnant
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Credit: NASA

Supernova shockwaves have just been spawned in a lab right here on Earth

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Jun 12, 2020, 1:46 AM EDT (Updated)

There are some things you can’t see through a telescope. Though supernovas are hard to miss, the origin of the intense shockwaves they generate can only be observed under a microscope.

Supernova remnants are powerful particle accelerators. Dead stars that collapse in on themselves and explode, releasing shockwaves into their plasma that are so powerful they blast out cosmic rays made up of electrons and other subatomic particles, accelerating these particles to nearly the speed of light. Space would look as if it were bubbling with light if you could actually see this aftermath. Though the phenomenon has remained something of an enigma, scientists from Stanford University’s SLAC National Accelerator Laboratory have now recreated the shockwaves (on a much smaller scale) without ever leaving this planet.

Because supernovas usually happen far out in deep space, the closest anyone on Earth can get to them is through the lens of a telescope. Even the most hi-res telescope out there is not advanced enough to image subatomic particles millions to billions of light years away. Through mini shockwaves and computer simulations, the team was able to get an unprecedented look at what happens to electrons during a supernova. Electron injection is the process by which electrons are infused into a particle accelerator. In this case, the particle accelerator is the immense shockwave from an astral explosion. There was just one question left.

“In most astrophysical shocks, the details of the shock structure cannot be directly resolved, making it challenging to identify the injection mechanism,” said Frederico Fiuza, senior staff scientist at SLAC, who led a study recently published in Nature Physics.

When a star explodes, its plasma, which consists of electrons and ions, slams into surrounding gas in what is known as a collisionless shock. This is a shock wave that goes from its pre-shock to post-shock state as particles from excited plasma interact while that plasma, which contains raging electromagnetic fields, is emitted and absorbed. The charged particles don’t head-butt each other but are instead pushed around by these electromagnetic fields before they are accelerated nearly to light speed. Here is where the problem lies. If the particles move across the shock so fast, something has to be accelerating them before that phase. But what?

In what could be the most intense game of laser tag ever, the scientists aimed superpowered lasers at carbon sheets to produce plasma. These plasma flows ended up racing toward each other. When the inevitable crash happened, what resulted was an artificial supernova remnant shock that could send electrons zooming close to the speed of light. Fiuza’s team was able to prove that all the characteristics of a supernova shockwave were there through optical and X-ray observations. They were also able to elucidate something about the shockwave’s origin: Electrons could reach the speed of light as soon as it formed.

Some things remain nebulous. It is still not exactly clear how the electrons were able to accelerate to a speed the human brain can barely fathom, but there may be an answer. Electrons emit X-rays from the moment they are accelerated to such high speeds, and measuring those X-rays could explain the difference in electron energies depending on how far they get from the shockwave. There are also other particles in supernova cosmic rays that haven’t been studied in depth yet. Protons might be able to tell us something that even spacecraft are not capable of finding out.

“Our observations provide new insight into electron injection at shocks and open the way for controlled laboratory studies of the physics underlying cosmic accelerators,” Fiuza said.

Laser tag for the win.

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