ИСТИНА

Intermediate mass black holes (IMBHs) are long-sought objects that bridge the mass gap between stellar mass black holes commonly produced as a result of stellar evolution, and supermassive black holes frequently found in the galactic nuclei. Despite of expected IMBH abundance, up to now only one such black hole, HLX-1, was reliably identified, which seems to bring more puzzles than answers, the main mystery being uniqueness of this object. In this talk I present the idea how to complement legacy X-ray data with new large ground-based surveys and obtain a list of accreting IMBH candidates meant to address "the IMBHs question" -- problem of fundamental importance in astrophysics. I shall describe how mature Virtual Observatory infrastructure as well as its emerging technologies help to get most out of rich archival data obtained during almost 14 years of XMM-Newton X-ray observatory operations, and how technical progress facilitates such research projects.