Fast Radio Bursts (FRBs) are one of the biggest astronomical mysteries of the last decade. First observed in 2007, astronomers have detected over two dozen instances of the powerful but fleeting signals from space. Researchers don’t know exactly what they are, but there have been plenty of proposals—including alien messages (of course), signals from collapsing black holes or neutron stars, and energy from a phenomenon known as cosmic strings. But as Hannah Devlin at The Guardian reports, new observations are getting us closer to the answer. The latest results suggest that the signals are emitted from areas with super-strong magnetic fields.
Almost all of the FRBs detected so far have been fleeting and non-repeating, which means it’s been next to impossible to track down their source. But there is one signal, dubbed FRB 121102 that has repeated itself multiple times. Last year, that repetition allowed researchers to trace the burst to a faint dwarf galaxy in the constellation Auriga that lies some 3 billion light years away.
Now, researchers have looked at measurements of those signals as well as 10 new bursts detected in August at the Arecibo radio telescope in Puerto Rico and confirmed by the Green Bank telescope in West Virginia, according to a press release. They determined that the bursts likely pass through a field of magnetized plasma, altering the signal. That process, called Faraday rotation, “twists” the polarization of certain radio frequencies in a certain way. Researchers found that the twist on FRB 121102 is 500 times greater than that found on any other FRB, which means the signals had to pass through an incredibly powerful, highly magnetic dense plasma field. The research appears in the journal Nature.
The latest finding is helping astronomers narrow down the type of environment that is in the vicinity of whatever object is producing the signal. “The only known sources in the Milky Way that are twisted as much as FRB 121102 are in the Galactic center, which is a dynamic region near a massive black hole. Maybe FRB 121102 is in a similar environment in its host galaxy,” Daniele Michilli of the Netherlands Institute for Radio Astronomy says in another press release. “However, the twisting of the radio bursts could also be explained if the source is located in a powerful nebula or supernova remnant.”
While that describes the environment near the source of the FRB, the cosmic object that can produce such a powerful signal is still a mystery. It is so powerful, it emits the same amount of energy our own sun produces in a day in just milliseconds. “This is exotic. If we had one of these on the other side of our own galaxy — the Milky Way — it would disrupt radio here on Earth, and we'd notice, as it would saturate the signal levels on our smartphones,” Cornell astronomer and co-author James Cordes says. “Whatever is happening there is scary. We would not want to be there.”
As Sarah Kaplan at The Washington Post reports, despite the new data, there are many mysteries to solve. For instance, are there two classes of FRBs—repeaters and non-repeaters? Or is there just one class produced by the same phenomenon? Second, the bursts from FRB 121102 are very jagged and oddly clustered, with many happening within the span of a second. Is that the way the bursts occur? or are intermediaries, like plasma fields, that fiddle with the signals before they reach Earth? And the signals only appear in the radio section of the electromagnetic spectrum.
“We were looking for it in X-rays, gamma rays, and there's nothing there,” co-author Shami Chatterjee tells Kaplan. “It’s a mystery. I say that as if I am disappointed, but let’s be real — there is nothing like a good mystery to try to figure out. And this is such a tantalizing mystery, and as time goes on we’re getting more clues.”
More clues may be coming shortly. Last year, work completed on China’s enormous FAST radio telescope, the world’s largest. It's still being calibrated, but will begin looking into the skies in the next few years. Later this year, the MeerKAT telescope in South Africa, with 64 dishes, will become operational and will later be incorporated into the Square Kilometer Array, which will take the title of world’s largest when it becomes operational in 2024. Hopefully one of those mega-machines will help us understand these mega bursts.