What term describes the challenging observational region for compact objects with masses between about 2 and 5 solar masses?

Answer

The mass gap

The mass gap refers to a region in observed data where objects weighing between roughly 2 and 5 solar masses are rarely confirmed, potentially representing the heaviest neutron stars or lightest black holes.

What term describes the challenging observational region for compact objects with masses between about 2 and 5 solar masses?
astronomystarsstellar evolutionblack holes