High-energy astrophysics and astroparticles study the most extreme phenomena in the universe: explosion of massive stars, formation and evolution of compact objects (neutron stars, black holes), acceleration of particles to relativistic energies, emission of gravitational waves or very high-energy neutrinos, etc. Current observations generally extend over the full electro-magnetic spectrum and sometimes up to the new non-photonic messengers. These multi-wavelength or multi-messenger observations are the key to understand the extreme physics in the sources. In the recent years, the multi-messenger area is becoming a reality with the first joint detection of gravitational waves (GW) from the binary neutron star merger GW170817, of its electromagnetic counterpart (short γ-ray burst and kilonova), and the discovery of the first cosmic neutrino sources associated with a bright and variable blazar. Despite many decades of observations, many open questions remain in the understanding of high-energy phenomena in the universe such as the origin of the dark matter in the universe, what is the influence of the compact objects (black hole, neutron star, etc.) on their environment, how massive stars explode at the end of their life, formation/growth of black holes, what is the nature, the origin and the role of the cosmic particles at high up to ultra-high energy, which sky will be revealed by the new-born GW and neutrino astronomies, etc. Many instruments (LSST, SKA, CTA, SVOM, advanced LISA, LIGO-Virgo, KM3NeT...) will be in operation during the next decade and beyond.
LISA will open the low-frequency GW astronomy (mHz frequencies), complementing the terrestrial instruments (few Hz to kHz range). At these low frequencies, sources include merging massive black holes (BH), compact objects captured by these BHs, the early inspiral of LIGO-Virgo-type merging BHs, and about a hundred million galactic white-dwarf binaries, of which about twenty thousand will be detected. This will push the studies of the physics of BHs in binary systems across the mass scale, from stellar objects of ∼ 10 M⊙ to super-massive BHs up to ∼ 108 M⊙ at the other extreme of the mass spectrum, though the entire universe. In the early 2030s, combining with electro-magnetic observations from ATHENA, JWST, ELT will provide unique science opportunities in the multi-messenger field.
Despite gravitational evidences, the nature and the properties of the dark matter remain elusive. Identifying this component of the universe is one of the major challenges for the next decade. The dark matter puzzle is an interdisciplinary question covered by article physic, cosmology and astrophysics communities. Solving these questions requires important efforts on theoretical studies including halo modeling, galaxy simulations, beyond the Standard Model phenomenology and detection rate calculations as well as continuous effort on the direct detection in accelerator (ATLAS) or in dedicated experiments (DarkSide, MadMax) and on the indirect detection using cosmic messengers such as anti-proton, positrons, neutrinos, gamma-rays in very propitious regions (Sun, Galactic Center or halo, dwarf galaxies...).
List of the main missions/projects associated to this theme: