The search for cosmological black holes: A surface brightness variability test

Recently it has been suggested that the majority of dark matter in the univ erse resides in the form of Jupiter-mass black holes distributed cosmologic ally. This population makes itself apparent by microlensing high-redshift q uasars and introducing pronounced variability into their observed light cur ves. While several arguments dismissing this hypothesis have been presented , a conclusive observational test is, alas, sadly lacking. In this paper we investigate the effect of a cosmologically distributed population of micro lensing masses on galaxies at low to intermediate redshift. The magnificati on of bright stars in these galaxies leads to small, but observable, fluctu ations in their surface brightness. The variability timescale for Jupiter-m ass lensing objects is of the order of a few months, and this population ca n be detected through a future space-based monitoring campaign of a field c ontaining z similar to0.5 galaxies. The monitoring of galactic surface brig htness will provide an effective test of the nature of dark matter on cosmo logical scales.