Measuring a Black Hole's Spin

The black hole in question resides 60 million light years away at the centre of the NGC 1365 spiral galaxy, is a mind-boggling 3.2 million kilometres in diameter, has a mass two million times that of our Sun and is spinning at a rather impressive 1.08 billion km/h. Astronomers can now say this with confidence, after combining the efforts of Nasa's Nuclear Spectroscopic Telescope Array (Nustar) — which measures high-energy X-rays — and the European Space Agency's XMM-Newton, which measures low-energy X-rays.