A cataclysmic energy flare ripped through our galaxy, the Milky Way, about 3.5 million years ago, a team of astronomers say.
They say the so-called Sifter flare started near the super massive black hole in the centre of the galaxy.
The impact was felt 200,000 light-years away.
The discovery that the Milky Way's centre was more dynamic than previously thought can lead to a complete reinterpretation of its evolution.
"These results dramatically change our understanding of the Milky Way," says co-author Magma Guglielmo from the University of Sydney.
"We always thought about our Galaxy as an inactive galaxy, with a not so bright centre," she added.
The flare created two enormous "ionisation cones" that sliced through the Milky Way.
The team - led by Professor Joss Bland-Hawthorn from Australia - used the data gathered by the Hubble Space Telescope to calculate when the massive explosion of high-energy radiation took place.