Ultra-High Energy Electrons Traced to Collisionless Shocks
Why in the news
Johns Hopkins University and Northumbria University researchers, publishing in Nature Communications, showed plasma shocks near Earth can supercharge electrons.
Key facts
- Data: NASA’s MMS, THEMIS and ARTEMIS missions studying solar wind meeting Earth’s magnetosphere.
- Site: the bow shock, where solar wind slows and passes energy to Earth’s magnetic field.
- 17 December 2017: foreshock electrons hit 500 keV, versus about 1 keV normally.
Collisionless shocks
- Energy moves through electromagnetic interactions in plasma, not particle collisions.
- Seen near pulsars, black holes and supernova remnants.
Electron injection problem
- Electrons need about 50% of light speed before diffusive shock acceleration works; the initial boost was unexplained.
- Repeated plasma interactions in the foreshock appear to supply it, possibly everywhere in space.
Significance
- Cosmic rays were mostly tied to supernovae; planetary bow shocks, such as those of close-in gas giants, may add to them.
- More research is needed to confirm this.