Physics

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 the most violent objects in the cosmos can offer the necessary conditions for that: supernovae with their explosion shock waves, magnetic fields of rapidly spinning neutron stars, colliding galaxies or energetic black hole cores of active galaxies.

An artist's drawing of a particle jet emanating from a black hole at the center of a blazar. Credit: DESY, Science Communication Lab
Some active galaxies, known as blazars, develop narrow twin jets of light and elementary particles, one of which is pointing to Earth, emitted from the poles along the axis of the black hole’s rotation. The picture of this year’s ICD shows one of these two jets. They are powerful cosmic engines that accelerate high-energy cosmic rays. But not only. When a blazar accelerates protons, pions are created as well which then produce neutrinos and gamma rays. Neutrinos are uncharged particles, unaffected by even the most powerful magnetic field. Because they rarely interact with matter and have almost no mass, neutrinos travel nearly undisturbed from their accelerators, giving scientists an almost direct pointer to their source. By using neutrinos and gamma rays we can point to the cosmic ray accelerators.

On the 22nd of September 2017, one of these neutrinos was detected at the South Pole by the IceCube Neutrino Observatory. It was sent 4 billion years ago from the blazar TXS 0506+056 in the constellation of Orion. This neutrino did not travel alone: gamma rays were detected as well by other telescopes on Earth and in space. This is the first observational evidence that cosmic rays, neutrinos and gamma rays are created in the same source. It also marks the dawn of multimessenger astrophysics: by combining information from different cosmic messenger —cosmic rays, neutrinos, gamma rays and gravitational waves — we can learn about the distant and extreme universe. To learn more about this visit this web page: multimessenger.desy.de.

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.IceCube,  KM3NeTMAGICTelescope ArrayVERITASCherenkov Telescope Array .