Talk about a long-distance call! Astronomers have stumbled across a mysterious radio signal that appears to have traveled from not just from outside of our solar system – but beyond even our Milky Way galaxy.

The largest cosmic ear in the world, the 305-metre-wide Arecibo radio dish in Puerto Rico, picked up a momentary burst of radio waves on Nov. 2, 2012. The signal itself was quite modest – nothing more than radio blip lasting only three one-thousandths of a second long. It was so fast that the human ear alone could not detect it, but its ramifications could be huge in the research community.

The same signal had been heard a few times before, but only by the Parkes Radio Telescope in Australia. Astronomers, however, questioned its origin, thinking that since only that one observatory was hearing it, it must be coming from close to our planet, most likely somewhere within Earth's environment. They thought it could have been an errant communication signal bouncing off the upper atmosphere or a satellite.

"It took a long time for me and for my collaborators to really believe its reality," said Victoria Kaspi, one of the lead investigators in this discovery and astrophysicist at McGill University in Montreal in an interview with Yahoo Canada News.

"We are inherently skeptical, and needed to consider every alternative before actually believing its reality."

But now that Arecibo has also picked up these mysterious bursts, it confirms to Kaspi and her international team that it indeed has a cosmic origin. The finding are published in the July 10 The Astrophysical Journal and shows that the signal is beaming out from the constellation Auriga, which is visible across the entire Northern Hemisphere.

Based on the other signals – totaling seven – which all appeared in different parts of the sky, researchers believe there may be thousands of these seemingly random fast radio bursts flashing over the whole sky every single day. But what's causing them?

Analyzing the incoming radio signals and how they appear to scatter over long distances, Kaspi 's team was able to calculate that they must have originated a whopping three billion light years away. That means that this radio signal left on its journey when life was just getting started on Earth and photosynthesis was kicking in.

"The degree of dispersion [of the signal] was far higher than we would expect to see if the source were in our Milky Way galaxy, so the distance then comes from an estimate of how far away a radio emitter must be in order to get such a large dispersion," Kaspi said.

So what's the source? Anything that can emit radio waves that travel across a large tract of the universe must have awesome power.

Indeed, astronomers have been scratching their heads. But leading the line of suspects are merging white dwarfs, a new kind of supernova, or possibly the most exotic: a magnetar – an ultra-strong magnetized neutron star.

The size of a large city, these burnt-out cores of massive stars sport the most extreme environments in the cosmos. They have extreme gravity and magnetic fields, and with only a handful known to exist, they really are a mystery to science.

Weird signals have perplexed astronomers for decades, and none have panned out to be aliens making long-distance calls to us.

For Kaspi, who specializes in studying magnetars and leads a pulsar-survey project, the excitement is only just beginning. At this point it's all speculation and the true nature of these radio signals remains an riddle to astrophysicists, she adds. Now efforts will focus on listening to large swaths of the sky at once to try and hunt down more of these fast bursts.

"This is super exciting and it's the sort of discovery we all hope to make," said Kaspi.

But the next challenge will be figuring out what they are, and that will be at least as fun as the original discovery!