Context _____________________________________________________

High-energy astrophysics studies the most extreme phenomena in the Universe: star explosions, the formation and evolution of compact objects (white dwarfs, neutron stars, black holes) and the study of their impact on their environment, particle acceleration to relativistic energies, gravitational wave emission, the creation of high-energy neutrinos, and so on. The emissions observed can be thermal or non-thermal, and can span the entire electromagnetic spectrum, although high-energy observations (X-rays and gamma rays) are often essential to understanding the extreme physics at work in the phenomena studied.

High-energy astrophysics is essentially an interdisciplinary field, bringing together particle physicists, nuclear physicists and astrophysicists. Understanding the acceleration of relativistic particles in the Universe and their interactions with matter calls on particle physics and the physics of astrophysical shocks and the interstellar medium. Studying dense matter in neutron stars brings together nuclear physicists and astrophysicists interested in compact objects. Deciphering the origin of elements requires knowledge of stellar evolution, nuclear physics and gamma-ray astronomy. Observatories set up to detect higher-energy rays are based on detection methods specific to particle physics, and their operation generally requires a good knowledge of particle physics and/or nuclear physics.

Priority Themes ___________________________________________

The PNHE is steered by a Scientific Council and structured around five unifying themes:

• The Universe as a Laboratory
• Compact Objects and their Environments
• Explosive Phenomena
• Cosmic Rays
• The new Messengers