A telescope perched aboard the International Space Station (ISS) spotted something very strange back in August: a sudden spike of X-rays surging out of a pulsar 11,000 lightyears away in the Sagittarius constellation. It was the brightest pulse of X-rays NASA has ever witnessed.

This particular explosion, from the pulsar SAX J1808, is called a Type 1 X-ray burst, according to a paper published in The Astrophysical Journal Letters. Pulsars are rapidly spinning and condensed cores left over from the death of a massive neutron star. As pulsars spin, they pulse high-energy radiation out across the universe at a regular interval.

“This burst was outstanding,” said astrophysicist and study author Peter Bult of NASA’s Goddard Space Flight Center and the University of Maryland, College Park. The X-ray burst released as much energy in 20 seconds as the sun does in almost 10 days, according to a statement from NASA. The pulsar spins at a rate of about 401 rotations each second.

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