Ferrario, Lilia2015-12-132015-12-13November 19703211585http://hdl.handle.net/1885/87046I argue that the observational evidence for white dwarf-white dwarf mergers supports the view that they give rise to ultra-massive white dwarfs or neutron stars through accretion induced collapse. The implications for the progenitors of Type Ia SNe are discussed.Keywords: Stars: Neutron; Stars: Supernovae; White dwarfs20042015-12-12