Eppur non si trovano: Comments on the Primordial Black Hole Limits in the Galactic Halo
P. Mróz, A. Udalski, M. K. Szymański, I. Soszyński, Ł. Wyrzykowski, P. Pietrukowicz, S. Kozłowski, R. Poleski, J. Skowron, D. Skowron, K. Ulaczyk, M. Gromadzki, K. Rybicki, P. Iwanek, M. Wrona, M. Ratajczak
TL;DR
This paper deconstructs Hawkins & García-Bellido's criticisms of OGLE-based microlensing limits on primordial black holes (PBHs). It highlights the transition from PSF-based photometry to Difference Image Analysis (DIA), demonstrating dramatically improved light curves and robust event classification that diminishes contamination from variable sources and transients. By analyzing OGLE-III/IV data, the authors report 13 microlensing events toward the LMC, with detection-efficiency-calibrated expectations for halo PBHs remaining far below those needed for a dominant dark-matter fraction, even under varied Milky Way halo models. Complementary comparisons with MACHO, EROS, MOA, and DESI+Gaia-based halo mass inferences reinforce that no large, unseen population of compact objects persists in the Galactic halo, leaving PBHs’ contribution to dark matter well below unity across the studied mass range.
Abstract
In a recent arXiv post, Hawkins & Garcia-Bellido raised doubts on the results of 20-yr long OGLE photometric monitoring, which did not find a large number of gravitational microlensing events in the direction of the Magellanic Clouds. These results implied that primordial black holes and other compact objects with masses from 10^{-8} to 10^3 M_solar cannot comprise a substantial fraction of the Milky Way dark matter halo. Unfortunately, the Hawkins & Garcia-Bellido post contained a number of scientific misrepresentations of our work. Here, we demonstrate that their arguments lack a solid basis or are simply incorrect. As we show below, "and yet they are not found" - compact objects (including primordial black holes) in the dark halo of the Milky Way remain undetected, despite extensive searches.