Lower-mass-gap Black Holes in Dense Star Clusters

Understand

The existence of compact stellar remnants in the mass range $2-5\,M_{\odot}$ has long been debated.

• This so-called lower mass gap was initially suggested by the lack of low-mass X-ray binary observations with accretors about $2-5\,M_{\odot}$, but it has recently been called into question following newer observations, including a lower-mass-gap candidate with a millisecond pulsar companion in the dense globular cluster NGC 1851.
• Here we model NGC 1851 with a grid of similar dense star clusters utilizing the state-of-the-art Monte Carlo $N$-body code \texttt{CMC}, and we specifically study the formation of lower-mass-gap black holes.
• We demonstrate that both massive star evolution and dynamical interactions can contribute to forming lower-mass-gap black holes.