The article Amazing rays as star succumbs to dark side talks about a very large black hole swallowing up a star. The report goes on to say that the only reason it was discovered was because it shot out a signal directly at our Solar System, by chance.
A discovery that was 3.8 billion years in the making, as our Solar System spins around and happened to collide with that signal at the right moment in time. Given that the universe is around 14 billion years old and this was only 3.8 billion years ago (the Earth may not have existed when this event occurred). But I digress.
This discovery implies to me that it's very hard to even detect significant events. That is, we have to be pointing our listening equipment at very minute areas of the sky to detect an astronomical event.
So even with our available array of detection hardware here on Earth as well as orbital telescopes, how much of the visible sky have we already scanned? And how long will it be until we've "scanned" the universe?
To help clarify the question, I know that there may be areas of the sky that may be completely void, so perhaps scanning "the relevant universe" is a more appropriate scope of this question, but if you can guestimate the whole visible sky, it would be interesting to know.