Hubble time! 🌌 Looking past its long spiral arms filled with stars and the dark threads of dust crossing it, your eye might be caught by the shining point at the centre of UGC 3478. This point is the galaxy’s nucleus, and indeed there is something special about it: it is a growing giant black hole which astronomers call an active galactic nucleus, or AGN. UGC 3478, located in the constellation Camelopardalis, is what is known as a Seyfert galaxy. This is a type of galaxy with an AGN at its core. Like all such “active galaxies”, the brightness that you see here hides a supermassive black hole at the centre of the galaxy. A disc of gas spirals into this black hole, and as the material crashes together and heats up it emits very strong radiation. The spectrum of this radiation includes hard X-ray emission, which clearly mark it out from the stars in the galaxy. Despite the strong brightness of the compact central region, we can still clearly see the disc of the galaxy around it, which ...