Flashes in the Sky

Every night, the sky changes. Stars explode as supernovae, black holes bend the light of other objects, and binary systems can erupt suddenly and spectacularly. To detect these events, continuous and precise monitoring of the entire sky is required—exactly what the Gaia spacecraft of the European Space Agency provided. The unmanned probe was equipped with a sophisticated optical system, including two telescopes and CCD detectors, similar to the light-sensitive systems used in modern cameras. Its purpose was to collect data on unexpected cosmic phenomena and record them rapidly.

During the Gaia mission (2014–2025), a unique early-warning system for exceptional cosmic events, called Gaia Science Alerts, was in operation. This system was developed with the participation of scientists from the Astronomical Observatory of the University of Warsaw and implemented with researchers from the University of Cambridge. Its task was to continuously analyze Gaia’s data to detect unexpected phenomena. Most frequently observed were exploding stars in late stages of evolution (supernovae), gravitational microlensing events—where the light of a background star is bent by a massive foreground object, cataclysmic stellar eruptions caused by sudden matter exchange in tight binary systems—and other cosmic “flashes.”

Over the eleven years of the mission, scientists and PhD students from the Astronomical Observatory UW daily examined and classified new phenomena, identifying the most interesting targets for follow-up observations. Data from Gaia were compared with ground-based observations, making a global network of telescopes essential. These included both large professional observatories and smaller amateur and school telescopes, which allowed astronomers to study each flash in detail, across multiple filters and nights.With support from the European Union, through the Horizon 2020 and Horizon Europe programs, the BHTOM.space system was created to automate the entire process. It coordinated all steps of the research: from detecting the event by Gaia, sending observation requests to ground-based telescopes, analyzing the images, and publishing the results. Teachers and students also participated in this international project—their observations contributed to real scientific publications, and they became co-authors of discoveries.