Limiting the Abundance of LIGO/Virgo Black Holes with Microlensing Observations of Quasars of Finite Size Esteban Gutiérrez, A. Jiménez Vicente, Jorge We thank the anonymous referee for ideas and comments, which greatly contributed to enhancing the scope of our paper. This research was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) with the grants AYA2016-79104-C3-1-P and AYA2016-79104-C3-3-P. J.J.V. is supported by the project AYA2017-84897-P financed by MINECO and by the Fondo Europeo de Desarrollo Regional (FEDER), and by projects FQM-108, P20_00334, and A-FQM-510-UGR20/FEDER financed by Junta de Andalucia. A.E.G. thanks the support from grant FPI-SO from MINECO (research project SEV-2015-0548-17-4 and predoctoral contract BES-2017-082319). We present a simple but general argument that strongly limits the abundance of primordial black holes (PBHs) (or other unknown population of compact objects) with masses similar to those determined by LIGO/Virgo from BH binary mergers. We show that quasar microlensing can be very sensitive to the mass of the lenses, and that it is able to distinguish between stars and BHs of high mass, when the finite size of the source is taken into account. A significant presence of massive BHs would produce frequent high-flux magnifications (except for unrealistically large sources), which have been very rarely observed. On the contrary, a typical stellar population would induce flux magnifications consistent with the observations. This result excludes PBHs (or any type of compact object) in the mass range determined by LIGO/Virgo as the main dark matter constituents in the lens galaxies. 2022-05-09T12:02:40Z 2022-05-09T12:02:40Z 2022-04-10 journal article A. Esteban-Gutiérrez... [et al.], 2022 ApJL 929 L17. [https://doi.org/10.3847/2041-8213/ac57c6] http://hdl.handle.net/10481/74758 10.3847/2041-8213/ac57c6 eng http://creativecommons.org/licenses/by/3.0/es/ open access Atribución 3.0 España American Astronomical Society