Mystery repeating radio signals coming from a galaxy three billion light years away have been detected for a second time. Scientists with the Breakthrough Listen initiative, a project launched by the likes of Stephen Hawking to detect signs of alien life, said 15 fast radio bursts (FRBs) had been recorded during a five hour observation period on August 26.

The discovery was announced in the Astronomer's Telegram and in it, the team noted that this was the highest frequency at which FRBs had ever been detected, and that it appears whatever is producing the bursts is currently in a “heightened state of activity.” Their findings will be reported in further detail in a forthcoming scientific journal.

FRBs were first detected in 2001 and in the years since around 30 different events have been recorded. They last just a few milliseconds and appear to be coming from somewhere deep in space, but pinpointing their location is extremely challenging. Most FRBs are detected in data long after the event has passed.

In 2016, scientists announced the first case of a repeating FRB— FRB 121102. By following the bursts, they were able to trace them back to a galaxy three billion light years away, but not to the actual source—it appeared nothing in this region of space could be causing them.

Since then, this part of space has been monitored closely. Using the Green Bank Telescope in West Virginia, the Breakthrough scientists discovered the bursts in the C-band—the highest frequency any FRB has ever been discovered in. This new data should provide a new view of FRBs, bringing us closer to working out what could be causing them.

Carole Mundell, head of Physics at the University of Bath, U.K., who was not involved in the latest discovery, tells Newsweek that the latest set of bursts is very exciting. “They’ve opened up the spectral window,” she says. Having a recording of FRB 121102 in a different frequency allows scientists to examine it from a different angle.

“When we go to higher radio frequencies it starts to give us an understanding of the emission mechanisms for what produces the light,” she explains. “At the moment we don’t know. The radiation in any FRB appears to be similar to a laser in a laboratory, which is unusual in cosmic sources, so it must be a very energetic process that produces this light. This is an extra little clue about what might be producing the light from that, in the hope we might figure out what the actual object is.”

There have been a number of suggestions about what could be causing the FRBs—which Mundell says may not all come from the same cosmic source. Before the repeating bursts were discovered, it was thought a one-off cataclysmic event could be causing them—potentially a dense neutron star or a black hole. Finding a repeating burst means whatever is causing FRB 121102 cannot be a single event. “It’s clear this is a system that has some fuel—that it has some mechanism for accelerating the material and producing the light and it’s able to keep on going in this active state,” she says.

What we do know is that strong magnetic fields are probably involved, as this is one of the ways to produce the radiation being detected. This could be related to a binary system where one object, such as a black hole or star, is being fed by the other. “We don’t know whether that’s the case with this one,” Mundell says. “But certainly something is providing fuel for these outbursts and how that is all configured is open for debate.”

At the moment, FRBs are in the extremely early stages of discovery with scientists trying to piece together the physics of what is going on. As more and more surveys search for FRBs, the number identified should grow over the coming decade. While having an example that repeats will help scientists work out what is causing that specific FRB, whether or not it will help us understand what is causing the others is unknown.

In the meantime, speculation about the source of FRBs continues. “Astronomers are generally conservative and none of us are saying it’s an alien civilization,” Mundell says. “That’s the one you hear most. We’ve learned from past history that while it’s important to look for these signals from other civilizations, this is three billion light years away so whatever produced it, it was a long time ago.”

She adds that the discovery of pulsars in the 1960s is a good lesson in jumping to conclusions about astronomical mysteries. At the time, people talked about the existence of “little green men” but instead it turned out to be an entirely natural event. “There are lots of undiscovered phenomenon in the universe and we’re just starting to scratch the surface,” Mundell says. “We have these pieces of a jigsaw but we don’t yet know how to put it together.”