Interaction of Rayleigh-Taylor Fingers and Circumstellar Clodlets in   Young Supernova Remnants
  We discover a new dynamical mechanism that significantly enhances the growth of Rayleigh-Taylor fingers developed near the contact interface between the supernova ejecta and swept-up ambient gas in young supernova remnants if the supernova remnant expands into a clumpy (cloudy) circumstellar medium. Our numerical simulation demonstrates that large Rayleigh-Taylor fingers can obtain a sufficient terminal velocity to protrude through the forward shock front by taking extra kinetic energy from vorticies generated by shock-cloud interactions. We suggest this mechanism as a means to generate the aspherical expansion of the supernova ejecta. Ambient magnetic fields are stretched and amplified as the Rayleigh-Taylor fingers protrude, possibly leading to strongly enhanced radio emission. The material in the protrusions originates from the ejected stellar material with greatly enhanced heavy elements. Therefore, it can be a strong X-ray emitter. The timescale for the Rayleigh-Taylor fingers to reach the forward shock depends on the size, mass density and distribution of clouds being engulfed by the supernova shock, although the details will require further numerical investigation. 
Byung-Il Jun, T.W. Jones (U. of Minnesota), and Michael L. Norman (U.   of Illinois)