  We study a new mechanism for deflagration to detonation transition in
thermonuclear supernovae (SNe Ia), based on the formation of shocks by
amplification of sound waves in the steep density gradients of white dwarfs
envelopes. Given a large enough jump in density a small pressure and velocity
perturbation, produced by the turbulent deflagration, turns into a shock down
of the gradient, where it will dissipate and heat up the media. With the right
frequency and amplitude the heating can be enough to initiate a detonation,
which can propagate backward and up the density gradient. We studied planar and
spherical geometry. In the planar case we made a parametric study of the
frequency and amplitude. We found it possible to obtain a detonation for
perturbations down to Mach number M=0.003. In the spherical case, geometrical
damping makes it harder to initiate a detonation, but considering a small He
atmosphere (<0.01 Msol) makes it possible again to obtain a detonation down to
small perturbation (M=0.002). In the context of thermonuclear supernovae, this
could be a mean to turn a turbulent flame producing sound waves to a
detonation.
