That's an easy one Swane. We don't. We can't know about anything happening anywhere until the light that comes from it reaches us. Whether it be the sun going out (about 8 1/2 minutes) or Andromeda collapsing into a supermassive black hole (2 1/2 Million years, never happen anyway
). So if eaither of these events happen we won't know about it til that last bit of light gets here