Breakthroughs

High-energy astrophysics is the study of the Universe through radiation and messengers emitted by high-energy or decaying particles. These particles are heated or accelerated close to deep gravitational potentials (such as black holes and neutron stars), large electromagnetic fields, shocks in diffuse media, or forged in stars. High-energy astrophysics uses the information from about 19 decades of energy of photon radiation and additional 10 decades covered by charged particles, protons and ionised nuclei named the cosmic rays, reaching 1022 eV, neutrinos and as well gravitational waves. It uses celestial objects with extreme conditions of matter and magnetic fields as laboratories to explore the laws of physics and their possible violations leading to new discoveries. Such studies involve many fields of modern physics and astrophysics and cosmology, particle and plasma physics, electrodynamics and optics, data science and instrumentation. After the first attempts in the 50’ies and the discovery of the first TeV source by Whipple in 1989, the Crab Nebula supernova remnant (SNR), the instruments H.E.S.S., MAGIC and VERITAS opened a new wavelength domain for astronomy with very-high-energy (VHE) gamma-rays (0.05–100 TeV). Radiation at these energies differs fundamentally from that detected by astronomical instruments at lower energies: TeV gamma rays cannot be generated thermally by the emission of hot celestial objects. The energy of thermal radiation reflects the temperature of the emitting body, and apart from the Big Bang, there is nothing hot enough to emit such gamma rays. Instead, high-energy gamma rays probe a “non-thermal” Universe, where mechanisms other than thermal emission allow the concentration of large amounts of energy into a single quantum of radiation. High-energy gamma rays can be produced in a top-down fashion by decays of hypothetical heavy.

The Milky Way viewed (from bottom to top) in gamma rays, visible and infrared light (H.E.S.S.).