Critical Behaviour and Universality in Gravitational Collapse of a Charged Scalar Field

We summarize results from a study of spherically symmetric collapse of a {\it charged} (complex) massless scalar-field \cite{Hod}. We present an analytic argument which conjecture the generalization of the mass-scaling relation and echoing phenomena, originally discovered by Choptuik, for the {\it charged} case. Furthermore, we study the behaviour of the self-similar critical solution under {\it external} perturbations – addition of a cosmological constant $\mathrm{\Lambda }$ and a charge-conjugation $e$. Finally, we study the scaling-relation of the black-hole charge. Using an analytic argument we conjecture that black-holes of infinitesimal mass are neutral or obey the relation $Q_{BH} \ll M_{BH}$. We verify our predictions with numerical results.