Black holes in a spin

摘要

Supermassive black holes, with masses of millions to billions times that of our Sun, are believed to exist at the centre of essentially every galaxy. When these monsters feast upon the gas (and possibly the stars!) within galactic centres, they release enormous quantities of energy, producing a phenomenon called an active galactic nucleus (AGN). Far from being dark and difficult to detect, the black holes in AGNs are the most luminous spectacles in the Universe. On page 449 of this issue, Risaliti et aV report observations of the AGN at the centre of the nearby galaxy NGC 1365 (Fig. 1) using the Nuclear Spectro-scopic Telescope Array (NuSTAR), a newly deployed X-ray observatory and NASA's latest addition to its fleet of space telescopes. By exploiting NuSTAR's ability to measure the high-energy X-ray spectrum of an AGN with unprecedented accuracy, the authors obtain an unambiguous measurement of the spin rate of this supermassive black hole, finding a spin that is at least 84% of the maximum theoretically allowed value.