Detecting isolated stellar-mass black holes in the absence of microlensing parallax effect

TL;DR

This paper proposes a new method for detecting isolated stellar-mass black holes through gravitational microlensing, focusing on events without detectable parallax signals, and identifies a candidate event that fits these criteria.

Contribution

It introduces a technique to identify black hole candidates in microlensing data without relying on parallax detection, expanding the search methods.

Findings

Most black hole microlensing events have undetectably small parallax signals.

OGLE-2006-BLG-044 is identified as a potential black hole event based on its long duration and negligible parallax.

Implications for future black hole searches in microlensing surveys.

Abstract

Gravitational microlensing can detect isolated stellar-mass black holes (BHs), which are believed to be the dominant form of Galactic BHs according to population synthesis models. Previous searches for BH events in microlensing data focused on long-timescale events with significant microlensing parallax detections. Here we show that, although BH events preferentially have long timescales, the microlensing parallax amplitudes are so small that in most cases the parallax signals cannot be detected statistically significantly. We then identify OGLE-2006-BLG-044 to be a candidate BH event because of its long timescale and small microlensing parallax. Our findings have implications to future BH searches in microlensing data.