Why Do We See So Few Black Holes in Massive Binaries?

Abstract

We offer a simple explanation for the small number of black holes observed in pairs with massive stars. In detached massive binaries, spherically symmetric accretion takes place. This accretion could result in effective energy release in the hard band only if the equipartition of the gravitational and magnetic energy of plasma is established (Shvartsmans theorem). However, we show that due to the magnetic exhaust effect this equilibrium is virtually never established for the actual magnetic fields observed on massive stars: Shvartsmans theorem does not work. As a result, it is virtually impossible to detect black holes in detached massive binaries by currently available means (mainly, through X-ray observations).