  The high velocities observed in supernovae require a relativistic treatment
for the equation of motion in the presence of gradients in the density of the
interstellar medium. The adopted theory is that of the thin layer
approximation. The chosen medium is auto-gravitating with respect to an
equatorial plane. The differential equation which governs the relativistic
conservation of momentum is solved in numerically and by recursion. The
asymmetric field of relativistic velocities as well the time dilation are
plotted at the age of 1 yr for SN 1987A.
