The powerful signal, which lasted for just milliseconds, could have been a fluke, but then the team found three more equally energetic transient flashes all far removed from the galactic plane and coming from different points in the sky.
Analysis later indicated that, unlike most cosmic radio signals that originate in the Milky Way or a nearby neighbor galaxy, these four seem to have come from beyond.
Whatever triggered the bursts has come and gone. The signals, detected between February 2011 and January 2012, were one-time events so little follow-up work can be done.
What is known is that in just a few milliseconds, each of the signals released about as much energy as the sun emits in 300,000 years.