How fast does a black hole spin? And how does it matter? An international team including Lawrence Livermore National Laboratory scientists has definitively measured the spin rate of a supermassive black hole for the first time. The findings, made by the two X-ray space observatories, NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) and the European Space Agency’s XMM-Newton, solve a long-standing debate about similar measurements in other black holes and will lead to a better understanding of how black holes and galaxies evolve.