Astronomy & Astrophysics Seminar: Self-similarity of the third type in ultra-relativistic blastwaves

Zoom: https://tau-ac-il.zoom.us/j/87230679135?pwd=Y1duRlArUkJwSnhaaXVscUU0azY3Zz09

Abstract:

A new type of self-similarity is found in the problem of a plane-parallel, ultra-relativistic blast wave, propagating in a powerlaw density profile of the form rho ~ z^{-k}. Self-similar solutions of the first kind can be found for k<7/4 using dimensional considerations. For steeper density gradients with k>2, second type solutions are obtained by eliminating a singularity from the equations. However, for intermediate powerlaw indices 7/4<k<2 the flow does not obey any of the known types of self-similarity. Instead, I will show that the solutions belong to a new class in which the self-similar dynamics are dictated by the non self-similar part of the flow. An exact solution to the ultra-relativistic fluid equations reveals that the non self-similar flow is described by relativistic expansion into vacuum, composed of (1) an accelerating piston that contains most of the energy and (2) a leading edge of fast material that coincides with the interiors of the blastwave and terminates at the shock. The dynamics of the piston itself are universal, and do not depend on the external medium.

Seminar Organizer: Dr. Jonathan Stern

Recording >