Science
Exploded star's magnetic field seems too weak to launch the highest-energy cosmic rays
AI-generated illustration
X-ray hotspots ahead of the shock wave from an exploded star suggest its magnetic field is too weak to boost particles to the very highest cosmic-ray energies. The finding helps explain a cutoff in its gamma-ray light.
~10 microgaussEstimated magnetic field strength just ahead of the shock
The facts
- 1Cosmic rays are fast-moving particles from space. Where those reaching energies up to the 'knee' (around a quadrillion electron volts) come from is still an open question in astrophysics.
- 2Shock waves from exploded stars are leading suspects. To push particles to such energies, the shock would need a strongly amplified magnetic field ahead of it to keep the fastest particles from escaping.
- 3The team found many X-ray hotspots reaching ahead of the shock in the remnant RX J1713.7−3946, using archived Chandra data. Their behaviour fits light from secondary electrons made when accelerated protons hit dense gas clumps.
- 4The size of those hotspots gave a physical scale. From it, the authors estimated that accelerated protons spread about 1 parsec ahead of the shock, which constrains the field strength to about 10 microgauss.
- 5That value matches recent simulations of magnetic field amplification, and it is too low to reach PeV energies. It explains the observed cutoff in the remnant's TeV gamma rays; the abstract does not say this applies to all remnants.
Why it matters
It offers a direct observational check on a long-debated step in how cosmic rays are made, and a way to judge whether other stellar shocks could reach PeV energies.
Sources
- Adapted from Communications Physics: Direct observational constraint on upstream magnetic field amplification reveals the particle acceleration limit in a supernova remnant · Yuya Kawabata, Takaaki Tanaka, Hiromasa Suzuki, Tsuyoshi Inoue · Source license
