Haven’t played the DLC either yet, not sure if that adds anything, but:
[Spoilers for mid-game]
!While you play, you’ll encounter clues that point towards the sun station being the reason for the sun dying, as it was built to make the sun go supernova and use the resulting energy to find the eye of the universe.!<
[Spoilers for late- to endgame]
!Later on, it turns out that the sun station is actually not the reason, as it just didn’t work as the Nomai planned. The sun is actually going supernova because the universe is dying as a whole, as you can actually see all around you, with loads of supernovae going off in the sky. Now sadly, there’s no explanation given for why that is happening much earlier than everyone expected, iirc. I guess that’s a final mystery that’s indeed left unanswered.!<
!Stars don’t go from yellow to supernova in 22 minutes. I’m with the Hearthians and the Nomai who are confused AF that the universe is dying. Drum guy was wrong that the universe is older than we thought, that’s a theory he came up with in 22 minutes because he had no time to investigate further. If you come back early in the loop and say the universe is old, he doesn’t believe you and tries to find an alternate theory, because that hypothesis just doesn’t make much sense.!<
Haven’t played the DLC either yet, not sure if that adds anything, but:
[Spoilers for mid-game]
[Spoilers for late- to endgame]