Giant Black Hole Spins at Half Light-Speed

Two remarkable things about a giant black hole called RX J1131 at the center of a galaxy some 6 billion light years away. One: it's the farthest black hole to have its spin measured. Two: it’s spinning at half the speed of light. That’s according to a report in the journal Nature. [R. C. Reis et al., Reflection from the strong gravity regime in a lensed quasar at redshift z = 0.658] 
 
Astronomers have wondered, do large black holes grow gradually via steady intake of material; or quickly, for example, in a merger with another black hole during a galactic collision. Spin offers clues.
 
If the merger idea is correct, lots of new material flowing in a single direction feeds a black hole, driving the spin faster one way.