We are in the universe we call our own, on the planet we call Earth, in the physics-set and known reality we assume. There is no flat-out "magic" or other things along those lines, so far as we know.
The universe we live in is occupied by more or less powerful beings with technology we can only barely understand. They have been at war with other beings for unfathomable time. And one of their strange and powerful weapons had its guidance system taken out. By colossal coincidence, it decided to head our way, and lock on to a nearby star within its detection range, Sol. Our sun. It's goal is simple, and used many times throughout a war long gone. Kill a star.
- No wormholes
- No FTL travel
- Weapon no bigger than 0.3 times Sol's mass
- No time travel
- No warp drives
- No black holes or singularities
- No dark matter or antimatter
- Must work in less than 3 years
- Must be impossible to completely shut down via human effort
Question: How do you completely extinguish or destroy a star, using a weapon within the realm of known physics?
Note that this is not at all the same as: Is there a way to create a bomb to destroy a star?, because this is referring to the realm of known reality.
Also note that I'm not asking for you to question my basis.