Negative mass singularities mimicking dark energy

One or two negative mass singularities are found to occur in static inhomogeneous spatially closed solutions to the Einstein equations. The singularities produce a positive Komar mass, and this decreases the size of the cosmological constant relative to normal matter. The energy density of a perfect fluid vanishes at the singularities and is finite elsewhere. Numerical examples of these static solutions are provided, and their stability properties are found to be similar to the Einstein static universe. In an expanding universe, the effect of the singularities is to push the acceleration towards more positive values. Given the sentiment that naked singularities are to be avoided, we review just how benign the negative mass singularity is.