New limits from microlensing on Galactic Black Holes in the mass range $10M_{\odot}<M<1000M_{\odot}$

TL;DR

This study used archival microlensing data from EROS-2 and MACHO surveys to set new constraints on the abundance of intermediate-mass black holes in the Milky Way halo, especially in the 10 to 1000 solar mass range.

Contribution

It provides the first combined analysis of EROS-2 and MACHO data to constrain the fraction of dark matter in the form of black holes within the specified mass range.

Findings

Black holes with 10-100 solar masses comprise less than 15% of the halo mass.

Objects around 1000 solar masses are unlikely to make up more than 50% of the halo.

Combined data restricts the contribution of compact objects to about 15% of the total halo mass across a broad mass range.

Abstract

We have searched for long duration microlensing events originating from intermediate mass Black Holes (BH) in the halo of the Milky Way, using archival data from EROS-2 and MACHO photometric surveys towards the Large Magellanic Cloud. We combined data from these two surveys to create a common database of light curves for 14.1 million objects in LMC, covering a total duration of 10.6 years, with flux series measured through four wide passbands. We have carried out a microlensing search on these light curves, complemented by the light curves of 22.7 million objects, observed by EROS-2 only or MACHO only over about 7 years, with flux series measured through only two passbands. A likelihood analysis, taking into account LMC self lensing and Milky Way disk contributions allows us to conclude that compact objects with masses in the range $10 - 100 M_{\odot}$ cannot make up more than $\sim 15\%$ of a standard halo total mass (at $95\%$ confidence level). Our analysis sensitivity weakens for heavier objects, although we still exclude that $\sim 50\%$ of the halo be made of $\sim 1000 M_{\odot}$ BHs. Combined with previous EROS results, an upper limit of $\sim 15\%$ of the total halo mass can be obtained for the contribution of compact halo objects in the mass range $10^{-6} - 10^2 M_{\odot}$.