  Studies of young clusters have shown that a large fraction of O-/early B-type
stars are in binary systems, where the binary fraction increases with mass.
These massive stars are present in clusters of a few Myrs, but gradually
disappear for older clusters. The lack of detailed studies of intermediate-age
clusters has meant that almost no information is available on the multiplicity
properties of stars with M $<$ 4 $M_{\odot}$. In this study we present the
first characterization of the binary content of NGC 1850, a 100 Myr-old massive
star cluster in the Large Magellanic Cloud, relying on a VLT/MUSE multi-epoch
spectroscopic campaign. By sampling stars down to M = 2.5 $M_{\odot}$, we
derive a close binary fraction of 24 $\pm$ 5 \% in NGC 1850, in good agreement
with the multiplicity frequency predicted for stars of this mass range. We also
find a trend with stellar mass (magnitude), with higher mass (brighter) stars
having higher binary fractions. We modeled the radial velocity curves of
individual binaries using The Joker and constrained the orbital properties of
27 systems, $\sim$17\% of all binaries with reliable radial velocities in NGC
1850. This study has brought to light a number of interesting objects, such as
four binaries showing mass functions f(M) $>$ 1.25 $M_{\odot}$. One of these,
star #47, has a peculiar spectrum, explainable with the presence of two disks
in the system, around the visible star and the dark companion, which is a black
hole candidate. These results confirm the importance and urgency of studying
the binary content of clusters of any age.
