Light, like anything else, must travel through space, and it can only go so fast. That said, at this very instant, that is the state of the universe as it is now, Betelgeuse may be no more and we humans may be unaware of that simply because the light depicting the star's demise has not reached us yet and is still journeying through space. Light moves so fast that here on earth we consider things happening at the instant we see them, but that simply isn't true. There is ALWAYS an infinitesimal amount of time between the instant an event occurred and the instant the light (or whichever stimulus it may be) reaches your sensory organs. With the vast distances involved when speaking of interstellar space, the amount of time between the instant an event occurs and the instant the light depicting said event reaches your eyes can be hundreds, thousands, even millions of years. IN FACT, if we could travel FASTER than light, we could outrun it and, in essence, look into our own past. But that's a whole 'nother bowl of noodles.
