"Elephant in the room" is an English metaphorical idiom for an obvious truth that is either being ignored or going unaddressed. The idiomatic expression also applies to an obvious problem or risk no one wants to discuss.
It is based on the idea that an elephant in a room would be impossible to overlook; thus, people in the room who pretend the elephant is not there have chosen to avoid dealing with the looming big issue.
What happens if a star dies and cools slowly (never explodes)? Well reader, it becomes something less massive, and much cooler... and the matter goes from plasma to gas, then to solids and liquids in accordance with standard thermodynamics.
Pretty cool right? Look, stars are all phase states too!