Understanding the origin and role of relativistic cosmic particles
Cosmic rays are very energetic charged elementary particles. They are one of the three major ingredients of the interstellar medium, playing a crucial role in the formation of the large-scale structures of the Galaxies, including the Milky Way. Cosmic rays, together with the intergalactic magnetic fields, prevent matter from collapsing due self-gravity. Reciprocally, the matter weight confines magnetic fields and therefore Cosmic rays in the Galaxy. Their dynamic balance among these three constituents shapes out Galaxy, ultimately regulating the astrophysical phenomena we observe. Despite the fundamental chore of cosmic rays, basic question such where do they originate and how do they fill up the Galaxy remain elusive: are they related to the central region of our Galaxy? how do they propagate? CTA will unveil many of these questions by mapping with unprecedented precision our Milky way, studying the by-product of cosmic rays on massive clouds and star formation regions along the plane. It will also devote hundreds of hours to the understanding of the Galactic center, in which the DESY researchers have a large expertise. Moreover, it will provide the most constraining results on the cosmic rays content in neighbor galaxies and starburst galaxies, providing a complete picture of how these elementary particles forge our Universe.
Probing extreme astrophysical environments
To produce gamma-rays, it is necessary to invoke acceleration of particles to extreme energies, beyond any experiment that can be conceived in Earth. These extreme energies can only happen in extreme astrophysical environments close to massive objects which relativist shocks propagating in collimated jets, such active nuclei or gamma ray bursts. This jets or gigantic explosions are believed to be related to merges of objects with extreme characteristics or collapses of massive galaxies, which result on an enormous release of energy not only in gamma-rays, but also via other messengers such as neutrinos or gravitational waves. These makes then unique multi-messenger transitional events, which is one of the areas in which DESY researchers are deeply involved. In the upcoming era of multi-messenger astronomy, CTA and DESY will play a fundamental role in providing triggers and the most sensitive monitoring of the highest energies’ counterpart of these spectacular events.
Exploring frontiers in physics
CTA will be the most sensitive instrument to search for the elusive dark matter particles at an energy range above a few hundred gigaelectronvolts. This includes both the search for very heavy dark-matter candidates predicted by supersymmetry and the lightest candidates, so called axion-like particles. The latter are searched for by DESY scientists by studying the gamma-ray spectra of active galactic nuclei (AGNs). AGNs are galaxies that contain a supermassive black hole that accretes large amounts of matter and forms enormous jets of relativistic particle plasma. In AGNs, particles can be accelerated to much higher energies than what is possible in man-made accelerators such as the LHC.
