Abstract:  : While the current vacuum energy of the Universe is very small, in our standard cosmological picture it has been much larger at earlier epochs. We try to address the question of what are possible ways to try to experimentally verify the properties of vacuum energy in phases other than the SM vacuum. One promising direction is to look for systems where vacuumenergy constitutes a non-negligible fraction of the total energy, and study the properties of those. Neutron stars could be such systems, and we discuss how to use the recent observation of neutron star mergers to try to learn about the inner core of the neutron star which may be dominated by vacuum energy.