Apparently, there is a gas cloud that about to be sucked into the black hole at the center of our galaxy. (Well, it happened 26,000 years ago, but we're just about to see what ... will have happened?) This gas cloud is expected to form (to have formed) a halo around the black hole.
Deviations from the predicted shape of the halo would indicate that Einstein’s theory of gravity needs revision.
That would seriously be something.