Comment by kbelder

You made me wonder about the orbital speed of a planet circling one of these supermassive black holes, and how fast it would be... and then I realized, of course, the orbital speed would approach the speed of light at the event horizon.

There's a SF story waiting to be written about a planet just over that radius, traveling at something like 0.99c. Years would takes seconds, and seem even faster since they'd be significantly time-dilated. Of course, they'd quickly spiral in.