This study investigates the evolution of Rayleigh-Taylor ( R-T ) instabilities in Type Ia supernova remnants that are associated with a low adiabatic index \gamma , where \gamma < 5 / 3 , which reflects the expected change in the supernova shock structure as a result of cosmic-ray particle acceleration .
Extreme cases , such as the case with the maximum compression ratio that corresponds to \gamma = 1.1 , are examined .
As \gamma decreases , the shock compression ratio rises , and an increasingly narrow intershock region with a more pronounced initial mixture of R-T unstable gas is produced .
Consequently , the remnant outline may be perturbed by small-amplitude , small-wavelength bumps .
However , as the instability decays over time , the extent of convective mixing in terms of the ratio of the radius of the R-T fingers to the blast wave does not strongly depend on the value of \gamma for \gamma \geq 1.2 .
As a result of the age of the remnant , the unstable gas can not extend sufficiently far to form metal-enriched filaments of ejecta material close to the periphery of Tycho ’ s supernova remnant .
The consistency of the dynamic properties of Tycho ’ s remnant with the adiabatic model \gamma = 5 / 3 reveals that the injection of cosmic rays is too weak to alter the shock structure .
Even with very efficient acceleration of cosmic rays at the shock , significantly enhanced mixing is not expected in Type Ia supernova remnants .