The nature of the binary system NGC1850-BH1 still debated: a system with a 11 solar masses black hole (Saracino et al. 2021) or with a sdOB star (El-Badry et al. 2021)?
In the last years several observational surveys were designed in order to detect stellar mass black holes, including both those which are actively accreting and black holes in a quiescent status. These observations are crucial to understand the real extent of the population of black holes in the Milky Way, and to understand the formation of massive stellar black holes
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