Final Fate of Subcritical Evolutions of Boson Stars

We present results from a study of Type I critical phenomena in the dynamics of general relativistic boson stars in spherical symmetry. The boson stars are modelled with a minimally coupled, massive complex field (with no explicit self-interaction), and are driven to the threshold of black hole formation via their gravitational interaction with an initially imploding pulse of massless scalar field. Using a distinct coordinate system, we reproduce previous results [1,2], including the scaling of the lifetime of near-critical configurations, as well as the fact that such configurations are well described as perturbed, one-mode-unstable boson stars. In addition, we make a detailed study of the long-time evolution of marginally subcritical configurations. Contrary to previous claims [1,2], we find that the end state in such cases does not involve dispersal of the bulk of the boson star field to large radial distances, but instead can be generically described by a stable boson star executing large amplitude oscillations. Furthermore we show that these oscillations can be largely identified as excitations of the fundamental mode associated with the final boson star, as computed in perturbation theory.