If we wish to learn more about the Necronauts' research, direct confrontation will not work. We'll need leverage. Maybe they’ll respond to blackmail. Go and find a piece of their armor; I’m fairly certain they can’t survive the Afterlife without fully-operational armor. They certainly wouldn't want their technology falling into curious hands.
In hindsight, that endeavor may have been superfluous since if they died, they would merely remain here indefinitely. Nevertheless, hold onto this item, as it will be valuable later. I shall reward you for your troubles.