Neutron star mergers, Gamma-Ray Bursts and the Origin of Gold

Almost twenty-five years ago we suggested in a paper titled: "Nucleosynthesis, neutrino bursts and gamma-rays from coalescing neutron stars" that gamma ray bursts (GRBs) arise in neutron star mergers. We combined this prediction with earlier ideas of Lattimer and Schramm to suggest that in addition these mergers are the sources of heavy r-process material in the Universe, or put differently gold, silver and other rare heavy (A>130) elements. In recent years there is an accumulation of indirect evidence that short GRBs indeed arise from such mergers. Last June the Hubble Space telescope observed a very weak Infrared signal that followed a short GRB. This gave further indication for this link. This IR signal is interpreted as a Macronova, a short-lived IR signal that arises from the radioactive decay of debris from a compact binary merger. If the interpretation is correct this implies that indeed a significant amount of heavy r-process material was formed in this event. Combining this with the rate of observed short GRBs this implies that neutron star mergers produce most, if not all, heavy r-process material. Further observations of IR excess following short GRBs could confirm this hypothesis within a few years from now and resolve the last mystery concerning the origin of elements in the Universe.