For a decade now, astronomers have been puzzled by phenomena called "fast radio bursts." These FRBs are what they sound like -- split-second radio signals -- and they're coming from a mysterious source (or sources) across the cosmos. Exploding black holes, magnetars, hypothetical blitzars and even aliens are among the suggested causes. Now, for the first time, scientists say they've traced one of the bursts to its source, but the revelation may only serve to deepen the mysteries of its origin.
A team at West Virginia University discovered the first FRB in 2007 using archived data from Australia's Parkes telescope collected in 2001. A dozen more bursts detected in subsequent years by different radio telescopes all seemed to be random one-off remnants of far-away colossal cosmic collisions reaching our world.
That is until an FRB signal that repeats itself was identified for the first time.
On Wednesday at a meeting of the American Astronomical Society in Grapevine, Texas, an international team of scientists detailed a major breakthrough: they've been able to trace that repeating signal to a specific galaxy, another first.
"We know that at least one of these FRBs originated in a discrete source within a distant dwarf galaxy located some three billion light-years beyond our Milky Way Galaxy," said Shriharsh Tendulkar of McGill University, a member of the discovery team.
The astronomers traced repeating FRB 121102, which was first discovered in November of 2012 at the Arecibo Observatory in Puerto Rico, to the surprisingly tiny galaxy in the direction of the constellation Aurigia using the Very Large Array in New Mexico and other large telescopes.
The revelation only deepens the mystery of this odd phenomena, because the cosmic address they pinpointed is not at all what you'd expect.
"That's weird isn't it? You'd expect to find FRBs where there are more stars... more stars means more neutron stars," Tendulkar told a room of reporters and scientists at the meeting. He went on to explain that neutron stars -- remnants of massive stars -- are among the top candidates to explain FRBs.
The findings, which the scientists refer to as the first "localization" of a fast radio burst, are published in the journal Nature.
Locating the source of an FRB for the first time also opens a new pathway for studying parts of space beyond our own galaxy.
"This detection has really opened the gates to a new realm of science," Sarah Burke-Spolaor, who worked on tracing FRB 121102 to its source at the National Radio Astronomy Observatory told the audience. "This phenomenon is so well-tuned to explore the universe, particularly the space between galaxies ... We can study the structure and the content of this empty space."
In other words, the discovery could give scientists a new technique to see and study what's otherwise invisible between galaxies.
The fact that FRB 121102 sends repeating signals eliminates an early theory that suggested all FRBs were basically aftershocks of huge cosmic cataclysms. Knowing FRB 121102's repeating signal comes from a tiny galaxy makes it unlikely there's space-shaking collisions or explosions happening there multiple times per day.
One possible explanation is that there's more than one type of FRB.
"I think that this is a huge breakthrough but also extremely puzzling," Prof. Matthew Bailes, who is at Australia's Swinburne University of Technology and was involved in the discovery of the first fast radio burst in 2007, told me. "The nature of the host galaxy - a dwarf, was a bit of a shock. The proximity to an active galactic nuclei even more intriguing. Are there two or one class of FRB? We'll need to find more to get all the answers."
Big stuff can happen in a dwarf galaxy though, as UC Berkeley astronomer and team member Casey Law points out. Small galaxies can play host to major events like superluminous supernovae and long gamma ray bursts that are connected to magnetars, a crazy kind of neutron star with a powerful magnetic field that can give rise to powerful bursts of x-rays and gamma rays.
"All these threads point to the idea that in this environment, something generates these magnetars," Law said. "It could be created by a superluminous supernova or a long gamma-ray burst, and then later on, as it evolves and its rotation slows down a bit, it produces these fast radio bursts as well as continuous radio emission powered by that spin-down."
There are other possible origin stories, though.
A hypothetical object caused by a spinning pulsar collapsing into a black hole dubbed a "blitzar" was basically conceived in 2013 as a way to explain FRBs.
The detection of FRB 121102 by multiple radio telescopes would appear to rule out the most embarrassing possible cause seen in the past - some signals picked up a few years ago seemed at first like more fast radio bursts, but were later determined to be caused by someone opening a microwave oven door while it was running at the Parkes Observatory.
Then there is the explanation that none of the scientists directly involved with pinpointing FRB 121102 have mentioned, but that will probably continue to be associated with FRBs until their mysteries are solved: aliens.
At least one scientific organization is already looking into that possibility.
METI International (the acronym stands for Messaging Extra-Terrestrial Intelligence) pointed the Boquete Optical SETI Observatory in Panama toward FRB 121102 starting Tuesday evening and has so far spent a total of about an hour searching for evidence of advanced civilizations in the neighborhood.
"That's not a lot of time for a phenomenon known to be intermittent and unpredictable. So far we've found nothing that looks like the telltale sign of extraterrestrial technology," METI International President Douglas Vakoch told me shortly after the press conference concluded Wednesday.
Vakoch doesn't think there's any call for jumping to conclusions about FRBs coming from ancient advanced alien civilizations just yet, but says investigating for the possibility is good practice for the day evidence of an alien civilization is detected and follow-up observations are needed.
Ironically, FRB 121102 itself actually helps discredit one of the early notions around FRBs that seemed to point to a pattern behind the bursts - a pattern that some believed couldn't be a coincidence and may have been designed by something intelligent, perhaps?
As it turns out, the pattern only applied to the first ten FRBs recorded and others that followed, including FRB 121102, didn't fit the pattern. Sorry, E.T. We haven't received your call just yet.
While we're just beginning to understand these strange space signals better through FRB 121102, there's likely to be many more opportunities on the way, as it's believed that if we could observe and process incoming data from the entire sky, we'd likely find that earth is actually being bombarded with FRBs all the time.
"Finding the host galaxy of this FRB, and its distance, is a big step forward, but we still have much more to do before we fully understand what these things are," team leader Shami Chatterjee of Cornell University said.
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