Dipolar boson stars as static two-body systems: an effective-one-body description

Abstract

Dipolar boson stars consist of two scalar-field lumps held in static equilibrium by the balance between gravitational attraction and scalar repulsion. The repulsion stems from a $π$ phase difference between the harmonically varying complex scalar field sourcing each lump. We construct sequences of these configurations numerically and describe them analytically as bound states of two boson stars within the effective-one-body (EOB) formalism. We map the EOB potential previously derived for the scattering of two boson stars onto an energy-dependent Schwarzschild-like radial potential. We find that the EOB-based analytical prediction for the binding energy of the system agrees remarkably well with the numerical values. The analytical prediction for the critical gravitational coupling beyond which no static equilibrium exists is also consistent with the numerical results.