Stellar-mass black holes in young star clusters: exciting news

Black holes (BHs) are among the most mysterious and elusive objects in the Universe. The recent discovery through gravitational waves of very massive BHs has challenged our understanding of stellar evolution in massive stars, moving the focus to high-density environments like star clusters, where merger cascades are most likely to happen. In this context, a systematic search for stellar mass BHs in star clusters would be crucial to add important pieces of information in this complicated puzzle.

Exploiting the technique developed by Giesers et al. 2018, 2019, we have recently started a large spectroscopic campaign with MUSE, to search for these objects in clusters of different ages. For two very young clusters in the Large Magellanic Clouds (NGC 1850, ~100Myr and NGC1846, ~1.5Gyr) we have recently secured ~15 epochs of observations spanning almost 2 years. First results show that a fair amount of stars in the clusters are in binary systems, with some of them showing evidence of orbit around BHs.

I will spend some time discussing the first BH directly detected in NGC 1850, which is in a binary system with a B main sequence star. The simultaneous modelling of both radial velocity and OGLE light curves allowed us to derive the main physical properties of the system, as well as a first BH mass measurement.

Such a detection is very important for clusters as young as 100 Myr, as this is the first step in constructing the initial mass function of BHs, which represents a long standing open question in astrophysics.