The relatively young research field of astroparticle physics has been developing dynamically over the last years. It connects

  • particle physics (describing the interactions of elementary particles) with
  • astrophysics (describing up to the biggest structures in the universe) and with
  • cosmology (studying the history of the universe).

One of the very interesting topics in astroparticle physics is trying to understand the acceleration mechanisms of cosmic ray particles to very high energies, much higher than accelerators on Earth can reach.

Only a few extreme cosmic objects can offer the necessary conditions for that: supernovae with their explosion shock waves, magnetic fields of rapidly spinning neutron stars or jets emerging from enormous black holes which can be found in the center of many galaxies. 

image credit: NASA, ESA, Hubble, HLA
processing & copyright: Domingo Pestana

But cosmic rays could also be accelerated by the gravitational forces created in the interaction of galaxies. One example is the system of two colliding galaxies, known as Arp 273 or the “Rose of Galaxies”. It lies about 300 million light years away toward the constellation of Andromeda. The larger of the two spiral galaxies, called UGC 1810, is shown in the image of this year's ICD. It is characterized by its striking blue outer ring which is made up of comparatively young, massive, blue hot stars. Its rose-like shape is created by the gravitational tidal pull of the companion galaxy below.

The universe is a big place and full of different accelerators. Cosmic rays drift around and get energy boosts from multiple sources. When cosmic rays happen to strike the Earth's upper atmosphere, they initiate Extended Air Showers. These events create thousands of secondary particles that simultaneously reach a small section of Earth's surface.
On the ICD we will focus on one question, which will be addressed by student experiments:

  • The zenith angle distribution of air shower particles
    Can you find out if the number of air shower particles arriving from the horizon is the same as from above? If it is not, what could cause this effect?

There are many scientific experiments with huge detectors that aim to unlock the secrets of cosmic rays. In principle their detectors apply similar techniques as the detectors used for the ICD. If you are interested, have a look at the websites of the following experiments: ANTARESAugerBAIKALFermiHAWC, H.E.S.S.IceCubeMAGICTelescope ArrayVERITASCherenkov Telescope Array .