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Astrophysical and laboratory hypersonic flows

  • Scaling consists to study with the same equations similar hydrodynamical flows. Scaling allows to study in the laboratory mechanisms which have much greater scales. It is used for various applications. This requires to verify if dimensionless parameters, like for instance the Mach number, are identical in both cases, from laboratory to space. Scaling argument, as it is not always possible, must be taken with care.
  • Radiative shocks are present in various astrophysical objects like supernovae, pulsating evolved stars, accretion flows. A radiative shock is strongly structured by the radiation. In particular, the heating of the compressed zone produces photons which ionize the cold gaz in which the shock propagates and thus creates a radiative precursor. The radiative shocks can, in practice, only be obtained on large scale powerfull installations like Z-pinchs and lasers.
    Figure 1: schematic view of a young star system composed from a protostar, an extended disk, accretion columns connecting the star to the disk and collimated jets orthogonal to the plane of the disk (Credit ESA)
    ESA
  • Blast waves characterises the propagation of a spherical shock waves, which is impulsively driven on a point source. The corresponding astrophysical situation is the supernova explosion which creates the fameous remnants when the shock propagates through the interstellar medium. Blast waves are usually produced in the laboratory by focussing ultrashort high intensity lasers for instance, on hydrodynamic gas jets.
    sn
    Figure 2: SN1987 A images observed with HST (Credit NASA)
  • Hypersonic jets are found in young stars, microquasars and Active Galactic Nuclei, and propagate over distances serveral order of magnitudes larger than those of the central object. Their complex interaction with interstellar medium leads to typical signatures, like shocks. The launching mechanism is attributed to magnetic field effects. Lasers and Pinches are able to produce well collimated jets.
    Figure 3 : Different stellar jets observed with HST (Credit NASA)
    HST
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