  Standard General Relativity assumes that, in the absence of classical matter
sources, spacetime is empty. This chapter considers and analyses the new
behaviours of the gravitational field that appear when one substitutes this
emptiness by a reactive vacuum, stemming in particular from the idea of vacuum
provided by quantum field theory. We restrict our study to spherically
symmetric configurations, and take a simple free quantum scalar field as a
proxy to more complicated formulations. Our analysis is split into a study of
static and of dynamical configurations. Under the assumption of staticity, we
find and describe the different asymptotically flat self-consistent solutions
that appear when using a vacuum Renormalised Stress-Energy Tensor (RSET) as an
additional source in the Einstein equations. Of particular interest is the
discovery that, as opposed to standard general relativity, the new theory
naturally contains static ultracompact stellar configurations which could
observationally be mistaken for black holes (BHs). Then, in our study of
dynamical configurations, we investigate the possibility of these same vacuum
effects changing the internal gravitational processes after an initial
gravitational collapse in a way which shows a path towards forming the
aforementioned ultracompact configurations. This has lead us to analyse several
dynamical situations seldom contemplated in the literature. Of special
relevance, we find that the inner horizon that all realistic BHs should contain
could inflate outwards quickly enough to meet the outer one before any
appreciable Hawking evaporation has taken place.
