Black hole binaries and light fields: Gravitational molecules

We show that light scalars can form quasibound states around binaries. In the nonrelativistic regime, these states are formally described by the quantum-mechanical Schrodinger equation for a one-electron heteronuclear diatomic molecule. We performed extensive numerical simulations of scalar fields around black hole binaries showing that a scalar structure condenses around the binary -- we dub these states gravitational molecules. We further show that these are well described by the perturbative, nonrelativistic description.