  Applying semi-classical Quantum Mechanics, the vacuum fluctuations within a
star are determined, assuming a constant mass density and applying a monopole
approximation. It is found that the density for the vacuum fluctuations does
not only depend linearly on the mass density, as assumed in a former
publication, where neutron stars up to 6 solar masses were obtained. This is
used to propose a simple model on the dependence of the dark energy to the mass
density, as a function of the radial distance r. It is shown that stars with up
to 200 solar masses can, in principle, be obtained. Though, we use a simple
model, it shows that in the presence of vacuum fluctuations stars with large
masses can be stabilized and probably stars up to any mass can exist, which
usually are identified as black holes.
