Pinpointed at last Bill Saxton, NRAO/AUI/NSF; Hubble Legacy Archive, ESA, NASA

For the first time, we have followed a fast radio burst home. While we’re still not sure what causes these brief barrages of radio waves, we now know where one of them comes from, giving us a new way to study their origins.

Fast radio bursts (FRBs) are some of the universe’s most elusive phenomena: powerful radio signals that flash from distant space for milliseconds and then disappear without a trace. They have been blamed on everything from black holes to extraterrestrial intelligence.

Because they’re so brief, and because radio telescopes can only watch a small area of the sky at a time, only 18 FRBs have ever been detected. Of those, only one has been observed to repeat: FRB 121102. Now, a team of astronomers has used a collection of radio telescopes around the globe to finally pinpoint this repeating burst.


“It is absolutely nailed down,” says Shami Chatterjee at Cornell University in Ithaca, New York, who presented the results at a meeting of the American Astronomical Society in Grapevine, Texas today. “Even two months ago, I did not think we could tell this full story, and now we can.”

Wimpy host

Chatterjee and his colleagues tracked down the FRB using the Karl G. Jansky Very Large Array, a group of 27 radio telescopes in New Mexico, and the 21-telescope European VLBI Network.

Together, these networks can achieve much higher resolution than any single radio dish. After observing nine more bursts, they located the FRB about 100,000 times more precisely than previous attempts with individual telescopes.

This boost in precision allowed Chatterjee and his colleagues to unambiguously associate an FRB with other signals for the first time. Persistent radio waves that the researchers discovered originating from near FRB 121102 are actually coming from exactly the same place, an extremely faint dot in the sky.

The location of the fast radio burst’s host galaxy Gemini Observatory/AURA/NSF/NRC

That tiny dot, FRB 121102’s home, is a dwarf galaxy. It’s around a tenth the diameter of the Milky Way, dim but still forming stars, and more than 2.5 billion light years away.

“Before this step was taken, we could still continue having endless arguments about exactly how far away the FRBs were and therefore what their energetics were and what they were coming from,” says Chatterjee. “Now we know.”

Sample of one

Knowing where an FRB comes from allows us to rule out some of the many proposed explanations for their origins. Since this example is so far away, it must be extremely energetic and bright – so it’s unlikely that any of the other FRBs we’ve seen come from our immediate neighbourhood.

Two explanations for FRB 121102’s origin still stand out. The first is that it could come from an active galactic nucleus: a bright region around a black hole in the centres of some galaxies that spews radio waves as it vaporises the gas and plasma around it.

But the researchers’ preferred explanation is that FRB 121102 and its constant radio companion are caused by the remnants of a supernova being energised by a young, rapidly spinning neutron star. Since the FRB’s host galaxy is similar to the surprisingly faint galaxies that produce the brightest supernovae, this scenario is an enticing fit – although it’s nowhere near proven yet.

“What we learn from these papers may not be applicable to FRBs more broadly,” says Peter Williams at the Harvard-Smithsonian Center for Astrophysics. It is possible that FRB 121102 is special and that most FRBs are of an entirely different, non-repeating type. “However, folks have looked for interesting objects at the positions of other FRBs and nothing particularly compelling has turned up. That’s consistent with the fairly wimpy host galaxy revealed by this work.”

Chatterjee shares that concern. “Our highest priority for the future is to find one more FRB that repeats,” he says. “Right now we are arguing from a sample of one, which is always a dangerous argument to be making.”

Journal references: Nature, DOI: 10.1038/nature20797 and Astrophysical Journal, DOI: 10.3847/2041-8213/834/2/L8 and DOI: 10.3847/2041-8213/834/2/L7