X-rays help astronomers detect rotating black holes

The team used an intermediate galaxy to get clear images of quasars made up of black holes, Chandra providing an image sharp enough to separate the many images resulting from the lens effect. From there, the microlens (in this case, the magnification using individual stars of the galaxy) allowed to detect the spin in question. The smaller the region emitting x-rays, the more likely it is that a black hole will turn rapidly.

And in some cases, the holes turn at an extremely fast pace. The hole of one of the quasars, Einstein's Cross, was spinning about as fast as theoretically possible – 70% of the speed of light. The others were running at about half that rate.

You will probably not see a lot of observations like this one. The gravitational lens, by its nature, requires an ideal alignment. This particular observation focused on the study of exceptionally far-off quasars up to 10.9 billion light-years away. These could nevertheless provide important information about the elusive objects by their very nature.