According to some reports, Betelgeuse might "be ready to explode into a supernova". It's luminosity has decreased "considerably" in the recent weeks.
If we consider the "stable period" as that when luminosity is stable, what is the time between a star beginning to dim (i.e. leaving the "stable period") and exploding as a supernova? To put it more crudely, for the case of Betelgeuse, how long might it be until it explodes as supernova? In the end, I want to know whether we are talking about a process that takes millions of years or rather is a "sudden", few weeks/months/years process that I can see in my lifetime.
I get the feeling the answer is somehow hidden in this part of the Wikipedia entry on supernovas, but I am not trained enough to see it. It probably depends on the actual size of the star (but in this particular question, we can take Betelgeuse as reference).