Abstract

The K−-meson of mass mk = 494 MeV is similar to an exciton, consisting of a strange quark, as particle, and ū antiquark, as hole, bound together to make the kaon. In dense nuclear matter the kaon feels an attractive mean field from the nucleons which lowers its energy appreciably. As soon as its energy is brought down to ∼ half of its rest mass, it becomes energetically favorable in neutron stars to replace electrons by kaons, the neutron stars becoming nuclear matter stars at higher density. The kaons form a zero momentum Bose–Einstein condensate.

The new equation of state of dense matter, with the inclusion of kaon condensation, is substantially softer than conventional ones, meaning the maximum mass of compact objects formed in the collapse of large stars is only ∼ 1.5 M⊙. With this equation of state, black holes are easy to form and it is estimated that there are ∼ 109 of them in our galaxy. In this sense, a large number of black holes is the “smoking gun” for kaon condensation.

Introduction

A Bose–Einstein condensation which is somewhat exotic, even from the nuclear and particle physics point of view, is kaon condensation, condensation of K−-mesons in a zero momentum state.