Astronomers have picked up a repeated fast radio burst for the first time. This find is the third paper in as many weeks to speculate on the origins of these mysterious signals, and is contradicts some of the previous observations.
Fast radio bursts (FRB) last just a few milliseconds and seem to come from distant galaxies. Up until now astronomers have spotted just a dozen or so, but of the Netherlands Institute for Radio Astronomy and his colleagues say they鈥檝e seen 10 more, all coming from the same direction as one spotted in 2012.
The original burst, known as FRB 121102, was picked up by the Arecibo radio telescope in Puerto Rico. Initial follow-up observations didn鈥檛 spot anything, but in May and June 2015 the team discovered 10 additional bursts, much to their surprise. 鈥淚t鈥檚 fair to say we were expecting to see none,鈥� says Hessels.
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Finding FRBs that repeat provides a clue to their origins. 鈥淚t tells us that this wasn鈥檛 some kind of cataclysmic explosion that destroyed the source,鈥� says Hessels, such as the merger of two neutron stars.
Instead, he thinks the signal must come from a rotating source that repeatedly throws radio waves in our direction, similar to the pulsars seen in our galaxy. 鈥淚f it is outside our galaxy, which it appears to be, it must be something like a pulsar on steroids,鈥� he says.
Cosmic conflict
The result contradicts a paper published last week by Evan Keane at the Jodrell Bank Observatory in the UK and his colleagues. They reported a connection between an FRB and a distant galaxy with a radio 鈥渁fterglow鈥�, which they believe was likely to be caused by the kind of catastrophic merger Hessels鈥檚 observation rules out.
鈥淓ither one of the two things is incorrect, or there are two different types,鈥� says Hessels. That鈥檚 not without precedent 鈥� similar signals known as gamma ray bursts puzzled astronomers until they realised the bursts came in both short and long varieties.
This week of the Harvard-Smithsonian Center for Astrophysics and his colleagues also reported they had seen a second afterglow from Keane鈥檚 galaxy, which shouldn鈥檛 happen if a merger is the cause. It could just be a coincidence, in which case we don鈥檛 know if the cataclysmic cause is possible. 鈥淚 don鈥檛 think last week鈥檚 paper provides any evidence one way or another,鈥� says Williams about Keane鈥檚 paper, but Hessels鈥檚 paper makes it clear that there must be a source of repeating FRBs. 鈥淒etecting this repeating signal is fundamentally a more robust result.鈥�
Ultimately, astronomers need to make more measurements of these fleeting signals to figure out the puzzle. Arecibo is the most sensitive radio telescope in the world, which could be why it is the only one to have picked up repeated FRBs.
Pointing it in the direction of other FRBs should clear things up, says Hessels. 鈥淚f, for a few more of those sources, we can find additional bursts, then it will look quite plausible that they all repeat,鈥� he says. 鈥淚t鈥檚 just a matter of sensitivity and how long you wait.鈥�
Journal reference: Nature, DOI:
