  The presence of exotic hadrons, such as hyperons and $\Delta$ isobars, in the
dense nuclear matter in their cores has been shown to produce important changes
in the properties of neutron stars. Within the quark-meson coupling model, we
show that the many-body forces generated by the change in the internal quark
structure of the baryons in the strong scalar mean fields generated in dense
nuclear matter prohibit the appearance of $\Delta$ isobars.
