A massive collision of galaxies sparked by one travelling at a scarcely-believable 2 million mph (3.2 million km/h) has been seen in unprecedented detail by one of Earth's most powerful telescopes. The dramatic impact was observed in Stephan's Quintet, a nearby galaxy group made up of five galaxies first sighted almost 150 years ago. It sparked an immensely powerful shock akin to a 'sonic boom from a jet fighter' -- the likes of which are among the most striking phenomena in the Universe.