For years, scientists have been perplexed by fast radio bursts (FRBs), which are energetic flashes of radio light in deep space that sometimes flare-up just once and sometimes repeat, occasionally in unexplained periodic patterns.
Now, astronomers have discovered a new and ultra-rare type of repeating FRB located some three billion light years from Earth, which is close to another unknown object that is emitting a persistent, but weaker, radio buzz. This combination, which has only been observed in one other FRB, could reveal new insights about the source of these mysterious signals, reports a study published on Wednesday in Nature.
Casey Law, a staff scientist at Caltech who co-authored the new study, said the discovery of the new burst was “a big surprise” because it was such a “a perfect ‘twin’” to another repeating burst, first spotted in 2012, that is also next to a persistent radio source.
“There are many ideas for what causes FRBs, but the association with a persistent radio source is very helpful in developing and testing models,” Law said in an email. “Some thought the first FRB was associated with a radio source by coincidence with some unrelated object in the same galaxy as the FRB. Our new discovery is the second FRB with a persistent counterpart (known as FRB 190520), which confirms that the first such example was not a fluke.”
“Now we actually need to explain this double mystery and why FRBs and persistent radio sources are found together sometimes,” he added.
Scientists have found about three dozen FRBs, most of which emit one quick blast of radio light before seemingly disappearing forever. A handful of sources display repeated bursts, including the newly discovered FRB 190520 and its earlier doppelgänger, FRB 121102. Though FRB 190520 and FRB 121102 seem to erupt at random times, other repeating bursts flash in clear periodic cycles.
The wide variety of observed features in FRBs makes it tricky to come up with a unified explanation to account for all of them, so scientists have suggested that perhaps multiple types of astronomical objects can emit these bursts, or that one source could change its emission patterns over the course of its evolution. Though FRBs may seem like tantalizing signs of alien intelligence, the overwhelming consensus is that they are natural in origin. Popular candidates for the strange flashes include eruptions from dead stars known as neutron stars, or highly magnetic “magnetars,” or perhaps tumultuous systems that contain black holes.
Law and his colleagues, who were led by Li Di of the National Astronomical Observatories of the Chinese Academy of Sciences, suggest that FRB 190520 and FRB 121102 might be baby neutron stars that are still surrounded in the messy detritus of the supernovae that made them.
However, we will need to find more of these rare bursts to better understand the mechanisms that produce them, and unravel the full story of FRBs as a whole. To that end, China’s Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single-dish telescope on Earth and the facility that spotted FRB 190520, is likely to find many more of these enigmatic bursts in the future.
“I am very excited about the implications for having a new class of source out there in the universe,” said Law. “For decades, astronomers thought there were basically two kinds of radio source that we could see in other galaxies: accreting supermassive black holes and star formation activity. There is a massive amount of literature that simply categorizes radio emission in other galaxies in an either/or sense.”
“Now we're saying that it can't be an either/or categorization any more!” he concluded. “There is a new kid in town and we should consider that when studying populations of radio sources in the universe.”