Low mass stars live WAY longer than even medium mass stars. But there is a limit as to how much mass an object must have before it can burn hydrogen and be considered a star. What if I found an brown dwarf that was 1 kilogram shy of becoming a star. So I go there in my spaceship and toss a 1.1 kg rock into the star. Would the object ignite into a star, then a fraction of a second later, after it lost 1.1 kg fusing hydrogen into helium, return to being a brown dwarf? Or would I have started a chain reaction that will permit the star to burn for hundreds of billions of years like all the other M dwarfs?