Scientists have discovered the biggest explosion seen in the universe since the Big Bang, a new study reports. The explosion took place at the center of a galaxy that’s about 390 million light years from Earth.

“We’ve seen outbursts in the centers of galaxies before, but this one is really, really massive,” said study co-author Melanie Johnston-Hollitt of the International Centre for Radio Astronomy Research, in a statement. “And we don’t know why it’s so big.”

She added that the explosion happened very slowly, taking place over hundreds of millions of years. It also released five times more energy than the previous record holder.