Fingerprint of a Binary Merger

Supernova 1987A, which was the first naked-eye supernova since Kepler’s supernova in 1604. It was an unusual supernova that in many respects defied theoretical expectations. It has long been suspected that these anomalies were the result of the merger of two massive stars some 20,000 years before the explosion, but so far there has been no conclusive proof. Here we present threedimensional hydrodynamical simulations of the mass ejection associated with such a merger and the subsequent evolution of the ejecta and show that this reproduces the properties of the triple-ring nebula surrounding the supernova in all its details.