  We show that the repulsive effects associated to the zero-point energies of
quantum fields are capable of supporting ultracompact stars that overcome the
compactness limits present in general relativity for any object in hydrostatic
equilibrium. These objects are exact self-consistent solutions in semiclassical
gravity that incorporate the backreaction of the renormalized stress-energy
tensor (RSET) of quantum fields in vacuum. We arrive at stars of striking
qualitative agreement through two independent modelings of the RSET, evidencing
the generality and robustness of this result. The main physical properties of
these novel black hole mimickers are reviewed.
