Astronomers have detected repeating blasts of radio signals coming from deep space. These short-lived signals are known as 'fast radio bursts' (FRBs), and although we've heard them before, they were always thought to be one-off events coming from random locations. But for the first time ever, researchers have now heard repeating signals, all emanating from a single unknown source outside our galaxy.
Ten blasts all coming from the same direction were detected last year in May and June - and when the astronomers looked back at the data, they found that another FRB in 2012 had originated from the same place, suggesting that something is happening there regularly to produce the extremely short and intense signals. We know what you're thinking right now (and we don't blame you), but let's be clear up-front that there are a whole lot of possible explanations for these strange bursts outside of aliens.
Ever since FRBs were first discovered back in 2007, astronomers have been unsuccessfully searching for any sign of them coming from the same spot twice - something that would help them figure out what the hell was causing them.
But last November, Paul Scholz from McGill University in Canada was going through months of old data collected by the Arecibo radio telescope in Puerto Rico, and spotted some unusual patterns - six FRBs arriving within just 10 minutes of each other, and four more spread out, all coming from the same place.
"I knew immediately that the discovery would be extremely important in the study of FRBs," he said.
Researchers don't have enough data to pinpoint exactly where the bursts are coming from, but the team is pretty sure they're from outside our galaxy, based on the amount of plasma they dispersed while getting here. That's a pretty complicated measurement, but basically the 10 newly detected FRBs, as well as the 2012 burst, all had three times the maximum dispersion measure that you'd expect from a source within the Milky Way.
That point of origin in itself makes the repeating radio bursts unique - the other 16 FRBs we've found all appear to come from within our galaxy - but the differences don't stop there. "Not only did these bursts repeat, but their brightness and spectra also differ from those of other FRBs," said one of the researchers, Laura Spitler, from the Max Planck Institute for Radio Astronomy in Germany.
This has led the researchers to suggest that the repeating bursts might actually be a whole new type of FRB that we've never seen before.
The timing of the discovery is somewhat coincidental, because just last week, we thought we were finally getting close to understanding FRBs once and for all.
Scientists had managed to pinpoint the exact location of one of the bursts for the first time - something that's now been called into question - and based on the age of the galaxy it came from, they suggested that the burst wasn't coming from early star activity and was instead from an explosive event - such as the collision of two neutron stars - which couldn't possibly be repeated.
But this discovery suggests that the opposite is true. In fact, that most likely explanation for the repeating FRBs is that they come from an exotic object such as a young neutron star rotating with enough power to regular emit the extremely bright pulses. These stars might not even belong to a galaxy, the researchers suggest.
The next step is to pinpoint exactly where these mysterious signals are coming from so that astronomers can get a better idea of the type of activity that's happening there.
"Once we have precisely localised the repeater's position on the sky, we will be able to compare observations from optical and X-ray telescopes and see if there is a galaxy there," said researcher Jason Hessels from the University of Amsterdam. "Finding the host galaxy of this source is critical to understanding its properties."
Of course, just because these repeating radio bursts appear to have a different origin to the one-offs doesn't mean that the hypothesis put forward last week is wrong - it just means that we now have a brand new class of FRBs, most likely with their own origin story, to figure out. And it's always a good day in science when we can get a new mystery to unravel. We can't wait to find out more.
The research has been published in Nature.