Formation and mergers of bosonic stars

In this talk I will firstly give a brief introduction on what bosonic stars are and why should we be interested in studying them. Then, I will present a study of the non-linear dynamics of both boson(scalar) and Proca(vector) stars, through numerical relativity techniques. I will depict three different physical scenarios. At first I will consider the spherically symmetric Einstein-(complex)Proca system and show how, starting with Proca field distributions that obey the Hamiltonian, momentum and Gaussian constraints, the self-gravity of the system induces the formation of compact objects, which, for appropriate initial conditions, asymptotically approach stationary soliton-like solutions known as Proca stars. Then I will further explore the dynamical properties of these solitonic objects by showing both head-on collisions and orbital mergers of equal mass spherically symmetric Proca stars. The last part of the talk will be about the formation of spinning bosonic stars, both scalar and vector case. This is the first fully non-linear numerical evolutions of the Einstein-(complex, massive) Klein-Gordon and Einstein--(complex, massive) Proca systems, to assess the formation and stability of spinning bosonic stars. In the scalar case the formation is transient; a non-axisymmetric instability always develops ejecting all the angular momentum from the scalar star. In the Proca case, by contrast, no instability is observed and the evolutions are compatible with the formation of a spinning Proca star. Our analysis suggests bosonic stars have different stability properties in the scalar/vector case, which we tentatively relate to their toroidal/spheroidal morphology.