Many Mergers Might Fill the Mass Gap [@Amen2026]

Stars of mass between 130-250 $M_{⊙}$ are thought to end their lives in PISN
Many BHs in the mass range of 45-120 are still observed
The paper proposes that the BHs in this mass range are actually formed via BBH mergers, including Hierarchical Mergers.
Looking to establish this theory via GW observation of hierarchical mergers.
1G + 1G mergers have the same spin axis’s and similar masses, as they evolved together. Whereas hierarchical mergers have differing properties
They created a model for both non-hierarchical and hierarchical mergers, and then combined said models with a mixture fraction'' to create a mixture model” (look into this more and add a full section or something about it :)) Fitting to this model allows for the population to filter itself into its respective subpopulations without enforcing the existence of said subpop.

Results

We see that …

hierarchical mergers start at $\sim 46 M_{⊙}$ , supporting that this may fill the mass gap
separate collection of hierarchical mergers around 16 solar masses
lack of hierarchical mergers between 20-40 solar masses