X-SHAPED galaxies which pump out radio waves may be the calling card of the most spectacular event in the Universe – the collision of supermassive black holes.
Radio galaxies normally spew out two jets of radio waves in opposite directions, which are thought to line up with the spin axis of a black hole at the galaxy’s core. But about 7 per cent of radio galaxies appear X-shaped, where the black hole’s spin axis seems to have flipped from one direction to another (see Graphic).
David Merritt of Rutgers University, New Jersey, wondered whether a merger between two black holes…
