ST Starkiller Base

So I have a question about this. It basically soaks up the sun. And then uses it to blast other systems out of existence. My question is how would it have been fired a second time? How was the sun still there after the first shot? Maybe there were two suns? If that's the case did they build this thing with the intention of only firing it twice ever?

My guess is that it takes the suns from other systems...but if that was true why did it go dark as they absorbed the sun?

Thanks for any insight.