[mac5732]

What I have seen is that this means there is a chance that the star will explode/implode somewhere down the line. Doesn't always happen but I would plan on it. I have had not only my one system reduced to astroids when this took place but on 2 occasions it also took out my adjoining system as well. Lost over 14 planets between both systems. As for warnings I have had anywhere from 0-3yr notice. The only thing you can do is ship your people out on transports to other systems and if you have the worm hole closer, close all adjoing worm holes to that system or you could lose 1 or all of them as well, if the star blows.... If you get a warning act fast don't wait, I'd always keep 1 or 2 transport in the system put them in mothballs until/if you need them.
good luck

just some ideas mac