报告内容 摘 要 |
It is generally accepted that the mechanism by which the heavy, neutron-rich elements found on Earth, like gold or uranium, are synthesized is the so-called rapid neutron capture process or simply r-proces. Its astrophysical origin, however, remains a mystery. For a long time, supernova explosions were the most promising scenario, but state of the art numerical simulations are not able to reproduce the necessary conditions for the r-process to occur. In contrast, compact object mergers, such as two neutron stars (NSNS) or a neutron star and a black hole (NS-BH), have shown to be a robust alternative. Not only a non negligible amount of matter is unbound in such events, but also the high densities and neutron richness of neutron star material offers optimal conditions for the r-process nucleosynthesis. The most common remnant of the merger of a NS-NS or a NS-BH system is a black hole surrounded by a torus of neutron star matter (BH-torus). We performed numerical simulations of the merger of two compact objects (NS-NS and NS-BH) and of the long term evolution of the BH-torus system, and carried out nucleosynthesis calculations of the ejecta in a postprocessing step. By taking into account the material which gets unbound from the torus, due to neutrino-driven winds or viscous transport, in addition of the dynamical ejecta from the merger, we can reproduce strikingly well the solar element abundances for A>90. Furthermore, if we assume that all the heavy r-process material observed in our galaxy has been produced in compact object mergers, we can estimate the galactic merger rate. The possible forthcoming detection of gravitational waves from NS-NS or NS-BH mergers by the advanced LIGO detectors will provide invaluable information about this fascinating astrophysical site. |
