Origin of the Ring Fingers in Supernova 1987A

We demonstrate that the fingers of dense gas protruding inwards from the equatorial ring of SN 1987A is a natural consequence of the interacting winds model invoked to explain the circumstellar rings. At early times in the formation of the circumstellar shell, the wind shocks must have been strongly radiative, leading to a thin, dense, shock-bounded shell. Such a shell is subject to the non-linear thin shell instability, albeit in a more complex geometry than the early planar studies of the NTSI. Using three-dimensional hydrodynamic simulations, we show that the observed characteristics of the ``string of pearls'' around SN 1987A are consistent with the canonical interacting winds model subject to the NTSI.