Gravitational waves from dynamical shape transition of protoneutron stars

Abstract

We describe the dynamical behavior of newborn neutron stars modelled as homogeneous rotating spheroids. The dynamical evolution is triggered by the escape of trapped neutrinos, providing the initial equilibrium configuration. It is shown that for a given set of values of the initial angular momentum, a shape transition to a triaxial ellipsoid configuration occurs. Gravitational waves are then generated by the breaking of the axial symmetry, and some aspects of their observation are discussed. We found a narrow window for both, the initial values of the angular frequency and the eccentricity, able to enable a dynamical shape transition, with their upper bound determined by the Kepler frequency. The energy and angular momentum carried away by the gravitational wave are treated consistently with the solution of the equations of motion of the system.