Scientific context

While shock waves appear as rare and impressive events to people living on Earth, they are, in fact, rather dull and common phenomena in space. Rooted in the evolution of stars and galaxies, shocks are produced by all astrophysical objects, at all stages and all scales, paving their evolutionary path with clear dynamical and radiative signatures. Stars are a particularly striking example as shocks are constantly generated, from the birth (jets, bipolar outflows, accretion shocks), through the life (stellar winds), and to the death (supernovae, supernovae remnants) of stellar matter. While striking, this tight link between shocks and stars is not unique, and similar examples could also be given for entire galaxies: shocks are simply ubiquitous in the interstellar medium.

Because they are a major - and sometimes an only - mean for the study of astrophysical objects, extensive works have been achieved during the past 40 years to develop sophisticated models of interstellar magnetized shocks. Through detailed treatments of the microphysical processes of the gas - including viscosity, ion-neutral coupling, gas-grain coupling, chemistry, atomic and molecular excitation, and radiative transfer - those models are able to follow the out-of-equilibrium dynamical and thermochemical evolutions of the matter in which a shock propagates. The resulting kinematics and radiative signatures predicted by the models can be compared with observations in order to deduce the local physical conditions of the shocked gas and relate the shock properties to the object and event that generates it. In response to the needs of the astrophysical community, the models are regularly improved to include additional microphyiscal processes, extend their domain of application, or perform more realistic treatments of their evolution (non-stationary models) and geometry (2D and 3D models). As a result, the current state-of-the-art shock codes are deeply versatile and can be used to study a great variety of environments, from stellar jets, diffuse turbulent interstellar gas, supernovae remnants, dense cores, to galactic outflows and gas in the circum-galactic medium.

Naturally, all these theoretical efforts are strongly motivated by observations, whose quality and volume keep increasing over time. Following the pioneering works performed with the Spitzer and Herschel space telescopes, the new generation of instruments, with their unprecedented spectral and spatial resolutions, now provides a detailed characterization of the chemical richness and the kinematics of individual or collective shocks, in both galactic and extragalactic sources. The widening of spectral bands of all telescopes (e.g. ALMA, NOEMA, SOFIA, CFHT, APEX) allows the simultneous detections of tens of atomic and molecular tracers, while the development of new observatories (e.g. CTA) provides the high energy counterpart. 

Goals and methodology