ИСТИНА

Nearly every massive galaxy harbors a supermassive black hole (SMBH) in its nucleus, The origin of SMBHs remains uncertain: they could have emerged either from massive seeds (100k-1M M_Sun) formed by direct collapse of gas clouds in the early universe or from smaller (100 M_Sun) stellar mass BHs. The latter channel would leave behind numerous intermediate-mass BHs (IMBHs, 100-100k M_Sun). Using data mining in wide-field sky surveys and applying dedicated analysis to optical spectra, we identified hundreds of IMBH candidates, which reside in galaxy centers and are currently accreting gas that creates optical signatures of type I AGN. 11 candidates were confirmed by X-ray emission as bona fide IMBHs. In the follow-up campaign, we identified 3 objects accreting close to the Eddington limit. We also re-measured virial masses for about 40 low-mass BHs (below 1M M_Sun) and demonstrated that scaling relations between SMBHs and their host galaxies (M_BH-sigma and M_BH-M_bulge) in the IMBH regime follow the trends established by more massive SMBHs. The very existence of numerous nuclear IMBHs supports the stellar-mass seed scenario of the massive BH formation.