Astronomy can be, in some ways, a lot like the classic board game Clue. Scientists explore a sprawling but ultimately contained world, collecting information and testing theories about a great mystery. You can’t cover every corner, but with the right combination of strategy and luck, you can piece together enough clues to reasonably guess the neat answer – who, where and how – encased in a little yellow envelope in the center of it all. .
Only, instead of a fictional killer, astronomers are trying to track down the source of strange flashes of radio signals reaching Earth from the depths of space.
Scientists have discovered hundreds of such flashes, known as fast radio bursts (FRBs), over the past 15 years. Signals are intense and fleeting things. They come from all directions in the night sky and sneak up on our telescopes. Most are unique pieces, never to be seen again. A few “repeating FRBs” have appeared more than once. Astronomers have gathered as much evidence as possible and traced the approximate origins of FRBs to the enormous mansion that is our universe. Almost all come from distant galaxies, while just one so far came from somewhere in our own Milky Way. But astronomers still haven’t understood polar, or how; they don’t know for sure what type of astrophysical objects produce these powerful radio wave emissions.
But astronomers have found a tantalizing new clue.
A team of researchers has detected a new FRB from a galaxy billions of light-years from Earth, and this one is stranger than all the others. Most bursts last only a few milliseconds, pulsing with such intensity that they glow as brightly as galaxies before disappearing. But this emission of radio waves lasted about 1,000 times longer: three whole seconds. And there was something unusual about the signal itself. Astronomers detected small pulses, peaking about every 0.2 seconds, during the three-second burst. The researchers had previously detected an FRB source that followed a noticeable pattern, producing millisecond flickers for several days before calming down and then restarting. But the flashes themselves were random. It was the first time that the signal itself featured such a precise rhythm.
“In the FRB world, this is definitely big news,” Sarah Burke-Spolaor, an astronomer at the University of West Virginia who studies FRBs and was not involved in the new detection, told me. “The main question we always ask ourselves with FRB is: what makes them? A strict periodicity like this would be major.
The existence of such a model supports the growing evidence that suggests the culprit behind FRBs is a neutron star, the remnant core of a once-giant star that has burned up its fuel. Professor Plum could be a pulsar, a type of neutron star that spins rapidly and spews beams of radiation from its poles. Or Miss Scarlet could be a magnetar, another type of neutron star, known for its strong magnetic fields. “It’s very difficult to design a natural clock like that, but pulsars are the only known emitting objects with enough momentum to behave that way,” Burke-Spolaor said.
The researchers behind the detection didn’t have enough to definitely pin the FRB to a pulsar, Shami Chatterjee, an astrophysicist at Cornell University and co-author of the new research, told me. They also don’t have a good explanation for why this signal was so intense. Perhaps unseen gravitational forces amplified the emissions from a pulsar as it headed our way, making them brighter for radio telescopes. Or maybe a magnetar is having a giant flare. The latest detection bears some similarities to radio emissions from pulsars and magnetars found in our own Milky Way galaxy, but the strange new signal sounds, well, stranger. “It’s all just very particular,” Chatterjee said.
At that time, you might be thinking, Okay, astronomers have their suspicions about what’s responsible for the FRBs, but they haven’t solved the case. Add to that the discovery of a surprisingly clear pattern, and you might wonder: Could it be aliens? No, sorry. “Periodic signals are very, very common from normal astronomical sources,” Sofia Sheikh, an astronomer at the SETI Institute who works to find signs of advanced technology beyond Earth, told me. These sources include pulsars and magnetars. “If the source was pulsing pi numbers or the Fibonacci sequence or something like that, then that would be a SETI story,” Sheikh said.
If pulsars can indeed produce FRBs, astronomers can study these flashes to help them solve other cosmic mysteries. Scientists have already used the rhythms of less mysterious pulsars in the Milky Way as a kind of astrophysical clock, allowing them to perform various tasks such as measuring the mass of Jupiter, studying the properties of the space between stars and even discover a diamond-made exoplanet, Burke-Spolaor said. In the case of the diamond planet, which also started with an unusual signal, the clues quickly piled up: when astronomers noticed an intriguing shift in radio emissions from a pulsar 4,000 light-years away, they realized the best explanation was the presence from a nearby planet. The planet, according to their analysis, was composed mostly of carbon and oxygen, and dense enough to crystallize into a world of diamonds.
Astronomers hope to stumble upon more FRBs like this in their search for our cosmic lands. The Canadian telescope that detected this burst is constantly looking for more, and future observatories could discover thousands of them each month. “With every step of the process with the FRBs, every answer we got comes with a lot of other questions,” Burke-Spolaor said. “This detection does the same thing.” So far, astronomers have only looked for FRBs that last a few milliseconds because they didn’t think the flashes could last much longer, and it’s possible “we could miss a bunch of FRBs that last a few seconds,” Vikram Ravi, an astronomer at Caltech who was not involved in the new research but who studies FRBs, told me. The history of FRBs is a long game, and scientists now know to expect sudden twists. The secret envelope remains closed, but astronomers still have many cosmic halls to explore, and each turn promises to reveal a new clue.