A life-force entity in open space
A life-force entity was a type of lifeform that could take on other forms and live as them.
In 2365, a life-force entity took on the form of a Human-Betazoid hybrid fetus and gestated rapidly in Deanna Troi, in an effort to learn about the lifeforms on USS Enterprise-D. Unfortunately, it gave off radiation that endangered the starship, so to spare the crew, the lifeform left. (TNG: "The Child")