New study furthers our understanding about the origins of energetic cosmic particles in the universe
A new study, published today in Nature Communications by a team including members from the QMUL Astronomy Unit, has shed new light on how shock waves throughout the Universe can accelerate electrons to high energies.
The MMS spacecraft. Credit: NASA.
Cosmic ray particles are ultra-relativistic particles traveling near the speed of light, permeating the universe. These particles are believed to be accelerated at the most powerful shock waves produced in the universe, the supernova remnant shocks of exploding stars. Shock waves are found everywhere throughout our universe and therefore constitute an important source for particle acceleration. However, the theory that successfully explains the acceleration of particles up to ultra-relativistic energies at shocks only works if the particles are already relativistic i.e. already have a high enough starting energy. For electrons in particular, the lack of a theory explaining the initial acceleration up to (mildly) relativistic energies has puzzled scientists for decades and is called the electron injection problem.
This new study by Dr Savvas Raptis from the Johns Hopkins University Applied Physics Laboratory, in collaboration with Dr Martin Lindberg from the Queen Mary University of London, uses data from NASA’s MMS and THEMIS/ARTEMIS spacecraft missions to uncover evidence of a multi-scale electron acceleration mechanism capable of accelerating low energy solar wind electrons up to (mildly) relativistic energies at Earth’s bow shock. The study suggests that the observed relativistic electrons are generated by a complex interplay of multiple acceleration mechanisms, including the interaction of electrons with various plasma waves, transient structures upstream of the shock, and the Earth's bow shock itself. The results add yet another piece to the puzzle of the long standing electron injection problem and helps further scientist’s understanding about particle energization in the universe.
This work has been published in Nature Communications: https://www.nature.com/articles/s41467-024-55641-9