may be the culprit, since symmetry is clearly broken in core-collapse supernovae:

(*i*) Observations show that neutron stars receive “birth kicks” giving them typical velocities of $\mathcal{O}(100)\,\mathrm{km\,s}^{-1}$ with respect to the center of mass of their progenitors. The most likely and straightforward explanation for these kicks are highly asymmetric explosions leading to neutron star recoil owing to momentum conservation.

(*ii*) Deep observations of supernova remnants show that the innermost supernova ejecta exhibit low-mode asphericity similar to the geometry of the shock front shown in Figure \[fig:full3d\].

(*iii*) Analytic considerations and also 1D core-collapse simulations show that the protoneutron star and the region behind the stalled shock where neutrino heating takes place are both unstable to buoyant convection, which always leads to the breaking of spherical symmetry.

(*iv*) Rotation and magnetic fields naturally break spherical symmetry. Observations of young pulsars show that some neutron stars must be born with rotation periods of order $10\,\mathrm{milliseconds}$. Magnetars may be born with even shorter spin periods if their magnetic field is derived from rapid differential rotation.

(*v*) Multi-D simulations of the violent nuclear burning in the shells overlying the iron core show that large-scale deviations from sphericity develop that couple into the precollapse iron 