One of the mysterious signals repeated, suggesting it might come from a pulsar like this one – but much stronger, and beyond our own galaxy. (EPA/NASA/Chandra X-ray Observatory)

Last week, scientists reported a huge step in the hunt for mysterious cosmic phenomena known as Fast Radio Bursts (FRBs). But now their results are being called into question by others in the field. Amid that controversy, a new paper has just hit the presses: For the first time ever, they've found an FRB that keeps repeating. Published Wednesday in Nature, the study provides evidence that FRBs come from a source other than the massive star collision suggested by last week's researchers.

FRBs are bright radio flashes that last just a few milliseconds, and until now have never been known to repeat. Scientists believe they might occur thousands of times a day, but to date less than 20 events have been detected. Last week's study – also published in Nature – claimed to have pinpointed the exact origin point of an FRB for the first time ever.

This is how scientists tracked down the location of a fast radio burst and confirmed that these short but spectacular flashes of radio waves originate in the distant universe. (Commonwealth Scientific and Industrial Research Organization (CSIRO))

Now some scientists are questioning whether the signal used to track down the galaxy associated with the FRB was actually related to the radio burst at all. And this new study adds another possible point of contention: Based on the apparent age of the galaxy pinpointed in the first study and the strength of the radio burst, researchers had suggested a collision of massive stars as the cause of the mysterious signal.

But massive collisions don't repeat – and now it seems apparent that FRBs can and do.

"I don’t think the final nail is in the coffin on that," Jason Hessels, corresponding author of the latest study, told The Post in reference to the other team's research."There are more observations that need to be done, but it seems less convincing than it did last week." It is possible, he and other experts said, that there is more than one kind of FRB out there – some sent out by massive crashes in space, and others coming from different, more sustainable sources.

Harvard University’s Edo Berger, who is a co-author on an as-yet-unpublished paper that sets out to refute the supposed FRB origin, was more blunt: "Essentially I would say that the whole rationale behind the paper has gone away within about two or three days of when it was published," he told The Post, explaining that he believes the signal described in that paper has lasted too long to be associated with an FRB, and is likely some other space phenomenon they stumbled upon by accident.

Evan Keane, an astronomer with the Square Kilometer Array Organization who led the first study, told The Post that he won't comment on the particulars of Berger's takedown until it's reviewed by other scientists and published in a journal. But Keane and Berger agree on one thing: The latest paper is the real deal.

"My initial thoughts on the paper are that it is quite exciting, and as it is repeating it is clearly not due to a 'one off’ event, like (say) a supernova, or merger of two objects; they would only happen once," Keane told The Post in an email. He wasn't surprised or concerned about implications for his own findings, since scientists have floated the idea of multiple FRB origins before, "but it is clearly excellent to see the repetition, and so clearly," he said.

The findings stem from a discovery made in November, when McGill University Ph.D. student Paul Scholz was working with FRB data from the Arecibo radio telescope in Puerto Rico, which is the largest of its kind. After months of gathering and analyzing more data from the same spot in the sky, Scholz, Hessels and their colleagues showed several bursts with properties consistent with those of an FRB first detected in 2012.

"This one I think is a really great result," Berger said. "It's a great clue for what might be causing this. It’s not a one off thing, it’s a stable system that can be active again and again and again."

What might that stable system be? The scientists suggest a super-powerful neutron star. These stellar zombies are the remnants of huge stars gone supernova. They're just on the cusp of becoming black holes, with just barely enough pressure in their cores to keep them from collapsing into oblivion. That makes them the densest stars in the universe, and scientists have a lot to learn about their behavior.

Such an origin would bring the FRB mystery full circle, Hessels explained: Scientists first found FRBs just over a decade ago when searching for pulsing neutron stars (or pulsars) inside the Milky Way.

"They came across this signal that didn't quite fit with what we knew," Hessels said. The distance implied by the properties of these signals placed them outside the realm of neutron stars inside the galaxy.

"So these new findings could suggest some kind of very extreme pulsating neutron star, spinning very fast, with a strong magnetic field. . . beyond what you'd find with one in our own galaxy. It would have to be a very rare type of source," Hessels said.

As with last week's paper, more work is needed to confirm these findings – and it will take even more detections to determine whether FRBs have one source or many. Pinpointing the exact location of the sources of multiple FRBs is vital in puzzling out their true origins. Three highly sensitive FRB-detecting instruments are set to open this year, so it's possible that FRBs won't be mysterious for too much longer.

"That could be a month from now or it could be five years from now," Berger said.

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