Final answer:
Red dwarf stars with the lowest mass can theoretically live over 10 trillion years because they burn their fuel very slowly. However, no red dwarf stars have run out of fuel because the Universe is not old enough.
Step-by-step explanation:
The lowest mass red dwarf stars have an extremely long lifespan, as they burn their fuel much more slowly than larger stars. These stars, which have a mass less than half of our Sun, can theoretically live for more than 10 trillion years. This is because they have a slower rate of nuclear fusion, and therefore consume their hydrogen fuel at a very slow pace. It's important to note, however, that this theoretical limit far exceeds the current age of the Universe, which is around 13.8 billion years. So despite the red dwarf stars' tremendous potential lifespan, in reality, there are no such stars currently in existence that have run out of fuel and died because the Universe isn't old enough.
Learn more about Red Dwarf Stars