Coming from far beyond the galaxy, an extremely energetic blast of radio waves has been snared by astronomers lying in wait. Lasting for just a few thousandths of a second, the burst is the first of an enigmatic class of objects to be observed in real-time, astronomers report today in the Monthly Notices of the Royal Astronomical Society.

Called fast radio bursts, these extreme pulses of energy last for just a fraction of a second. They’ve confounded astronomers – who have no idea what they are – since West Virginia University’s Duncan Lorimer reported the first burst in 2007. At the time, it appeared as though the beam of radio waves had traveled roughly 3 billion light-years before colliding with Earth. That’s a reasonably far distance, even by astronomical standards. But not everyone believed the team’s interpretation. Skeptics suggested the burst’s signal could be coming from Earth’s atmosphere, or from inside the galaxy, or even that it was an artifact of the telescope itself, located at the Parkes Observatory in Australia.

Indeed, for five years, that Parkes telescope was the sole spotter of fast radio bursts, and eventually observed another half-dozen or so.

That changed in November 2012, when the Arecibo Observatory spotted a fast radio burst. Like the Parkes signals, it looked as though it came from billions of light-years away. While the observation strongly suggested the bursts were not a telescope artifact, scientists still had yet to see one in real time: All of the observations so far had been pulled from data that were at least a few weeks old.

Then, on May 14, 2014, Swinburne University’s Emily Petroff spotted a fast radio burst in the act of blasting. She and her colleagues determined the signal came from as far as 5.5 billion light-years away and was mildly polarized, suggesting a magnetic field somewhere near its origin has aligned the waves in particular directions.

Petroff had designed a program specifically to spy on these bursts, and once the radio pulse had been detected, she rallied a legion of telescopes to stare at the thing. Tasked with peering deep into the cosmos, the group of 12 telescopes quickly returned data suggesting there was no easily identifiable astrophysical source. The lack of a discernible afterglow eliminated some of the more mundane possibilities, such as distant supernovas or long gamma-ray bursts.

So what are these fast radio bursts? The short answer is, scientists still don’t know. “There are more theories than there are bursts,” Lorimer said last year. Some of those theories implicate rather exotic-sounding, very dense objects: Colliding black holes or neutron stars, evaporating primordial black holes, imploding neutron stars, or enormous flares erupting from magnetic neutron stars, called magnetars.