Fast radio bursts, or FRBs, are intense millisecond bursts of radio waves of unknown origin. The first FRB was discovered in 2007, and since then, hundreds of these fast, cosmic flashes have been detected from various, distant points across the universe. Many FRBs emit extremely bright radio waves that last only a few milliseconds at most before disappearing completely, and about 10% of them are known to repeat and have patterns.
One resource used to spot them is a radio telescope called the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, at the Dominion Radio Astrophysical Observatory in British Columbia, Canada. This telescope, in operation since 2018, continuously observes the sky and, in addition to fast radio bursts, is sensitive to radio waves emitted by distant hydrogen in the universe. Astronomers using CHIME spotted something on December 21, 2019, that immediately caught their attention: a fast radio burst that was “strange in many ways,” according to Daniele Michilli, a postdoctoral researcher at the MIT Kavli Institute for Astrophysics and Space. Research. The signal, named FRB 20191221A, lasted up to three seconds — which is about 1,000 times longer than typical fast radio bursts. Michilli was monitoring the data as it came in from CHIME when the explosion occurred. The signal is the longest-lasting fast radio burst to date. “It was unusual,” Michilli said. “Not only was it very long, lasting about three seconds, but there were periodic peaks that were extremely precise, emitting every split second—boom, boom, boom—like a heartbeat. This is the first time that the signal itself is periodic. “ While FRB 20191221A has yet to repeat itself, “the signal is formed by a train of successive peaks that we found to be ~0.2 seconds apart,” he said in an email.

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The research team doesn’t know the exact galaxy the burst came from, and even the estimate of a billion light-years away is “very uncertain,” Michilli said. While CHIME is ready to look for radio bursts, it is not so good at locating their points of origin. However, CHIME is being upgraded through a project where additional telescopes, currently under construction, will observe together and be able to triangulate radio bursts in specific galaxies, he said. But the signal contains clues about where it came from and what might have caused it. “CHIME has now detected several FRBs with different properties,” Michilli said. “We’ve seen some that live in clouds that are very turbulent, while others look like they’re in clear environments. From the properties of this new signal, we can tell that around this source, there’s a plasma cloud that should be extremely turbulent”. When the researchers analyzed FRB 20191221A, the signal was similar to emissions released by two different types of neutron stars, or the dense remnants after the death of a giant star, called radio pulsars and magnetars. Magnetars are neutron stars with incredibly strong magnetic fields, while radio pulsars release radio waves that appear to pulsate as the neutron star spins. Both stellar objects create a signal similar to the flashing beam from a lighthouse. The fast radio burst appears to be more than a million times brighter than these emissions. “We think this new signal could be a magnetar or pulsar on steroids,” Michilli said. The research team will continue to use CHIME to monitor the skies for more signals from this radio burst, as well as others with a similar, periodic signal. The frequency of the radio waves and how they change could be used to help astronomers learn more about the expansion rate of the universe. “This detection raises the question of what could cause this extreme signal that we have never seen before, and how we can use this signal to study the universe,” Michilli said. “Future telescopes promise to discover thousands of FRBs a month, and at that point we may find many more of these periodic signals.”