Cosmic Particle Accelerators

Charged cosmic particles' paths are being deflected by the magnetospheres from cosmic objects like the Earth, the Sun, stars, the Milky Way and other galaxies. Therefore, it is almost impossible to determine their source. Only charged particles with very high energies manage to bypass these deflections allowing a rough estimation of the location of their origin.

By measuring the energy and the flux of charged cosmic particles, the following three categories have been defined:

• Particles with energies up to 10⁹ eV are mainly produced by the Sun. The solar wind and solar flares accelerate electrons and protons.
• Particles with energies from 10¹⁰–10¹⁶ eV are mainly generated by galactic sources within our Milky Way. Cosmic accelerators could be pulsars, binary star systems and the shock waves of supernovae.
• Particles with energies in the range 10¹⁶–10²⁰ eV are very rare and assigned to extragalactic sources. Processes in active galactic nuclei and in the vicinity of black holes could accelerate particles to such high energies. But many questions remain unanswered, since none of the very high energy particles, that have been measured, could be successfully connected to a known source. In addition to that it remains unclear if these particles are protons or light nuclei and if an upper limit for the particle energy exists.

Charged particles are not the only product of cosmic sources. Neutral products like high energy gamma radiation (photons) and neutrinos are not affected by magnetic fields. Especially the gamma telescopes of H.E.S.S., MAGIC and VERITAS operating since the beginning of the new millennium have been detecting and investigating hundreds of galactic sources. With the planned 80-100 Cherenkov telescopes of the CTA experiment much more detailed insights into cosmic accelerators will be possible.

The weakly interacting neutral neutrinos would be ideal messengers for the production processes in galactic and extragalactic sources. Due to their very low interaction probability with matter most of them can penetrate great areas of the universe. But this advantage reverses itself if one wants to detect them on Earth. Even with the giant IceCube detector embedded in the ice of the South Pole only few very high energy neutrinos have been detected since 2011. Neutrino astronomy requires much larger detector volumes which are in preparation, with DESY contributing to this project as well.