Anyone familiar enough in this area that can help me answer these questions:
-gravitational waves also propogate at c so how did they escape the event horizons from which they originated?
-what and where was/is the "more energy than all stars emit as light in the universe"--10^34 megatons--released from? From matter in the accretion disk orbiting the black holes?
-the article says these two were spinning non-uniformly. Can we know if the bh's are spinning or just the stuff around them?
1. The waves didn't originate from inside the event horizons, but from the area around the black holes, where space is still very heavily warped.
2. Imagine you have two serious dents in some stiff plastic sheet. By tapping on the plastic with a hammer, you can't get rid of them, but you can sort of move the dents around. Now imagine that you maneuver the dents towards each other, so they merge into one bigger dent, and as that happens the sheet makes a dull thumping sound as the rigid material snaps into a radically different shape. That's a little like what happened here.
3. Yes, black holes maintain the spin they had before they became black holes (and in fact their angular momentum is vastly increased in the process, just like any spinning thing that reduces its radius).
Since black holes are rotationally symmetric they cannot shed angular momentum via gravitational waves since the production of those requires some asymmetry[0]. But as a sibling post pointed out they can impart some of their angular momentum on objects within the ergosphere which then may escape and carry away the energy.
Before merging, yes, they do shed angular momentum before merging. In fact, if you calculated the angular momentum of two maximally spinning black holes, you'd realize that if you could combine them, it would larger than the maximal possible spin of a single black hole with the combined mass. They must and will radiate this away as gravitational waves before merging.
How would a non-rotating black hole be possible? Wouldn't it be impossible for any source material to lack spin entirely? Or is it a purely theoretical thing?
I like your analogy on #2, but
To get to a more precise answer to the question, can't we just say the energy that was released came from the potential energy between the two?
-gravitational waves also propogate at c so how did they escape the event horizons from which they originated?
-what and where was/is the "more energy than all stars emit as light in the universe"--10^34 megatons--released from? From matter in the accretion disk orbiting the black holes?
-the article says these two were spinning non-uniformly. Can we know if the bh's are spinning or just the stuff around them?