Using the Fermi Gamma-Ray Space Telescope, astronomers have found that the shattered remains of the 1572 supernova event known as Tycho supernova live on in high-energy gamma rays, providing vital insight into the generation of cosmic rays. The team’s interpretation of the LAT observations, combined with additional data from ground-based facilities and with radio and X-ray data, imply that a process called pion production best explains the high energy emission. In this process, a proton traveling close to the speed of light strikes a slower-moving proton, creating an unstable, lower-mass particle called a pion, which almost immediately decays into a pair of gamma rays. Applied to Tycho’s star, somewhere within the remnant, protons are being rapidly accelerated and then interacting with slower particles to produce gamma rays.
Many younger remnants, like Tycho’s, tend to produce more high-energy gamma rays than older remnants. According to Stefan Funk, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), jointly located at SLAC National Accelerator Laboratory and Stanford University, Calif., the gamma ray energies reflect the energies of the accelerated particles that produce them, and we expect more cosmic rays to be accelerated to higher energies in younger objects because the shockwaves and their tangled magnetic fields are strong.