Astronomers think they know what caused the brightest ever gamma-ray burst, which was observed in March: a tightly beamed jet of matter that happened to be aimed almost directly at Earth, coming from 7.5 billion light years away, more than halfway across the universe.

This animation shows how astronomers think light from a gamma-ray burst called 080319B was released. A narrow jet punched though the outer layers of a collapsing star; this was followed by a wider, less energetic beam (NASA/Swift/Cruz deWilde)

Despite the immense distance, it would have been visible with the naked eye at dark sites on Earth for 40 seconds.