A critical analysis of the recent OGLE limits on stellar mass primordial black holes in the halo of the Milky Way

ABSTRACT This paper is a response to recent claims that a population of primordial black holes in the Galactic halo has been ruled out by the Optical Gravitational Lensing Experiment (OGLE) collaboration. This claim was based on the latest results from the OGLE microlensing survey towards the Large Magellanic Cloud which failed to detect even the number of events expected from known stellar populations. In particular, their results are completely inconsistent with the results of the massive compact halo object (MACHO) survey which detected a population of compact bodies in the Galactic halo which could not be accounted for by any known stellar population. The discrepancy between the results of these two groups has a long history, and includes problems such as different choice of photometric passbands, quality of light curves, microlensing event selection, detection efficiency, self lensing, and halo models. In this paper it is demonstrated that these issues not only account for the discrepancy between the OGLE and MACHO results, but imply that the OGLE observations can put no meaningful constraints on a population of primordial black holes in the Galactic halo.