Search for Black Holes in the Galactic Halo by Gravitational Microlensing

TL;DR

This study combines long-term microlensing data from multiple surveys to constrain the abundance of black holes and other compact objects in the galactic halo, finding they constitute less than 20% of the halo mass.

Contribution

It presents a novel combined analysis of extended light curves from EROS-2 and MACHO surveys to detect long-duration microlensing events, improving constraints on dark compact objects.

Findings

Compact objects with masses between 10^{-7} and 200 solar masses make up less than 20% of the halo mass.

Black holes lighter than 1000 solar masses do not constitute more than 50% of the halo.

Extended light curve analysis enhances detection sensitivity for long-duration microlensing events.

Abstract

Black hole-like objects with mass greater than $10 M_{\odot}$, as discovered by gravitational antennas, can produce long time-scale (several years) gravitational microlensing effects. Considered separately, previous microlensing surveys were insensitive to such events because of their limited duration of 6-7 years. We combined light curves from the EROS-2 and MACHO surveys to the Large Magellanic Cloud (LMC) to create a joint database for 14.1 million stars, covering a total duration of 10.6 years, with fluxes measured through 4 wide passbands. We searched for multi-year microlensing events in this catalog of extended light curves, complemented by 24.1 million light curves observed by only one of the surveys. Our analysis, combined with previous analysis from EROS, shows that compact objects with mass between $10^{-7}$ and $200 M_{\odot}$ can not constitute more than $\sim 20\%$ of the total mass of a standard halo (at $95\%$ CL). We also exclude that $\sim 50\%$ of the halo is made of Black Holes (BH) lighter than $1000 M_{\odot}$.