Supernova Explosions, Black Holes and Nucleon Stars

In the collapse of large stars matter is formed at supranuclear densities. At a density ρ ∼ 3ρ 0 , where ρ 0 is the nuclear matter density, K − ‐mesons replace electrons, and go into a Bose condensate. This soft equation of state gives a maximum mass for neutron stars of ∼1.5 M ⊙ . It is argued that the last nearby supernova, SN 1987A, went into a black hole. A new scenario of binary neutron star evolution is developed which results in the two masses in a given binary being nearly equal and all neutron star masses lying in a narrow band 1.3 M ⊙ < M NS < 1.5 M ⊙ .