Most of about 50 known stellar-mass black holes are (or were) in binaries (X-ray binaries and GW mergers). Single black holes, also those constituting a fraction of Dark Matter in the Milky Way, can be detected using the gravitational microlensing technique.
I will present the current status of the black hole hunt using OGLE and Gaia projects, which survey millions of stars in order to spot rare temporal brightenings due to black holes passing in front of distant stars.
I will present how astrometric measurements from the Gaia mission being collected now will yield measurement of the mass of the lens in the currently on-going events. However, in order to correctly recognise a lensing black hole the dense photometric coverage, lasting months to years, as well as high-res spectroscopy of the source are necessary. LCO has been a key contributor to this effort providing well-sampled light curves for black hole lens candidates.
I will also present the OPTICON network of small (<2m) telescopes scattered mostly around Europe, which would benefit from coordinated observations in the time-domain astronomy. The LCO's expertise in that field and, in particular, TOM Toolkit and AEON system, will be crucial elements in the planned improvements of the network's operation.