A black hole detected in the young massive LMC cluster NGC 1850
Dreizler, S.; Da Costa, G. S.; Cabrera-Ziri, I.; Usher, C.; Bastian, N.; Saracino, S.; Hénault-Brunet, V.; Gieles, M.; Kamann, S.; Guarcello, M. G.; Husser, T. -O.
United Kingdom, Italy, Sweden, Spain, Germany, Australia, Canada
Abstract
We report on the detection of a black hole (NGC 1850 BH1) in the ~100-Myr-old massive cluster NGC 1850 in the Large Magellanic Cloud. It is in a binary system with a main-sequence turn-off star (4.9 ± 0.4 M⊙), which is starting to fill its Roche lobe and is becoming distorted. Using 17 epochs of Very Large Telescope/Multi-Unit Spectroscopic Explorer observations, we detected radial velocity variations exceeding 300 km s-1 associated with the target star, linked to the ellipsoidal variations measured by the fourth phase of the Optical Gravitational Lensing Experiment in the optical bands. Under the assumption of a semidetached system, the simultaneous modelling of radial velocity and light curves constrains the orbital inclination of the binary to 38° ± 2°, resulting in a true mass of the unseen companion of $11.1_{-2.4}^{+2.1}\,{\rm M}_{\odot }$. This represents the first direct dynamical detection of a black hole in a young massive cluster, opening up the possibility of studying the initial mass function and the early dynamical evolution of such compact objects in high-density environments.