Contributed Talk - Splinter ISM

Thursday, 24 September 2020, 14:00   (virtual room F)

Rayleigh-Taylor-unstable astrophysical fluid flows

Michael Schulreich, Dieter Breitschwerdt
Center of Astronomy and Astrophysics, Berlin Institute of Technology

The Rayleigh-Taylor instability (RTI) is an interface instability that occurs when a light fluid pushes into a heavier one, seeking to reduce their combined potential energy. It occurs in many man-made and natural flows at various scales, from the pouring of milk into coffee, to inertial confinement fusion, to superbubbles (SBs) and supernova remnants (SNRs) in the interstellar medium. The characteristic finger-like structures arising from this can be nicely observed, e.g., in the Crab Nebula and Tycho's SNR. The RTI is the result of baroclinic torque created at the perturbed interface by the misalignment of the density and pressure gradients. The latter is usually caused by an external acceleration. In the case of young SNe and SBs, this is given by the deceleration of the expanding shell and thus directed out of the cavity. Whereas the density gradient across the contact discontinuity, which separates the ejected medium from the swept-up one, points inwards. In contrast to most terrestrial flows, however, the acceleration here strongly varies over the dynamical timescale, which is why classical growth rate formulas are not applicable. We present an analytical solution to the problem of time-dependent RTIs in their early stage of evolution, obtained from linear stability theory, and validate this using high-resolution hydrodynamical simulations.