Shocks are disturbances created by a perturber/object/fluid moving through a fluid faster than the local speed of sound, causing an abrupt change in pressure at the boundary between the two.

Typical examples are bow shocks where planetary atmospheres and solar winds meet, named after the analogous shocks produced on water by the bow of a ship.

Most shocks in space plasma are collisionless, because particle densities are too low for direct collisions between particles to convert the shock’s energy into heat. Instead, this is done by electromagnetic forces.

Collisionless shocks are thought to be a site in which cosmic rays can accelerate to relativistic speeds (near the speed of light), a process known as relativistic electron acceleration.

However, a lack of direct observational evidence has limited scientists’ understanding of how these structures work.

“Astronomers have sought the origins of cosmic rays since their discovery more than 100 years ago,” Dr. Savvas Raptis from the Johns Hopkins University Applied Physics Laboratory and colleagues said in a statement.

“These energetic particles can come from many sources, including supernovas and eruptions from the Sun.”

“When solar cosmic rays reach Earth, they can trigger space weather effects that disrupt satellites, communications, and power systems.”

“NASA missions showed how some electrons become highly energized in a region near Earth called the foreshock, where solar particles first encounter Earth’s magnetic field.”

“Scientists suspected the same process was responsible for accelerating high-energy particles in foreshocks at other planets and astrophysical systems, but they could not confirm it until now.”