Περίληψη :
Most of about 60 known stellar-mass black holes were found in binaries (X-ray binaries and GW mergers). Gravitational microlensing is the only tool capable of detecting single black holes, which are not interacting with anything. I will present our long-term project aiming at discovering and studying the microlensing black holes with the OGLE, Gaia and forthcoming Rubin/LSST surveys. Microlensing non-detections towards the Magellanic Clouds have put strong limits on the compact dark matter content in the Galaxy Halo, while the statistical studies of microlensing events towards the Galactic Centre, revealed a continuum of masses of dark lenses and hint at a lack of the mass gap between neutron stars and black holes.
However, in order to study individual events and obtain the masses of individual lenses it is crucial to measure the size of the Einstein Radius, which defines a separation between the lensed images and is a physical parameter degenerated in the classical microlensing light curve model. This is possible en masse only with the Gaia space mission, which scans the entire sky and provides not only brightness and colour temporal evolution for nearly 2 billion stars but also positional time series with sub-milliarcsecond precision. I will describe how we search for ongoing microlensing events within daily Gaia data using the Gaia Science Alerts system and how their photometric, spectroscopic and interferometric follow-up is conducted. I will discuss the first candidates for dark lenses from Gaia obtained with preliminary Gaia astrometric data. I will also present a network of 100 telescopes coordinated under the BHTOM.space project, which provides long-term photometric data for microlensing events from Gaia as well as any time-domain target, from supernovae to quasars.
