In a galaxy three billion light-years from Earth is a peculiar object that continually sends out extremely short, but powerful radio bursts. And astronomers don’t know what it is.
The object is producing something called a fast radio burst, or FRB. While 30 FRBs from objects throughout the universe are known to date — the first one discovered in 2007 — only one is known to repeat this millisecond-long radio emission: FRB 121102.
Though they’re not completely understood, it’s believed FRBs are caused by rapidly spinning neutron stars, small dense stars left over from supernovas. And yes, some people have even suggested aliens. But nothing is known for certain, and it’s even less understood why this particular one is producing an average of one every few hours.
Ever since the revelation that FRB 121102 repeats — discovered by Canadian Paul Scholz while he was a PhD student at McGill University in Montreal — people have been using this unique star to try to unveil the mysteries behind FRBs.
Now, using the William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico, a team of international astronomers have found this FRB exhibits some particular behaviour most associated with objects near black holes.
The visible-light image of host galaxy to the fast radio burst FRB 121102. (Gemini Observatory/AURA/NSF/NRC)
The new data shows that the radio bursts display something called Faraday rotation, where radio emissions need to pass through dense, highly magnetized plasma (a form of ionized gas).
“Really the only [similar] environments that we’ve seen are in the centre of our galaxy, the Milky Way, near the galactic centre black hole and also other galactic centres,” Scholz, who was a co-author of the study published in Nature this week, told CBC News.
Young neutron star possible cause
But that doesn’t mean the puzzle’s been solved: the researchers believe there could also be a second explanation that shows somewhat similar traits: a dense nebula surrounding a young neutron star. And by young, that could be anywhere from dozens of years old to thousands, a mere blink of an eye when it comes to stars that could be potentially millions of years old.
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But astronomers have never seen anything produce such a high Faraday rotation.
“My PhD student, who typed in the commands and did the analysis, when it popped up on his screen, I half-jumped out of my chair,” said corresponding author of the study, Jason Hessels.
And how high is it? Scholz explains that when astronomers see objects with Faraday rotation measurements of radians per square metre in the 50s or 100s, they consider that high. This object is producing a Faraday rotation near 100,000.
“Ultimately the flashlight itself is the neutron star, and that’s shining through this material that’s between us and the source. And that material in this case is very close to the source,” Hessels said. “Think of the neutron star as being a very clean flashlight and the Faraday rotation is imparted by this magnetized cloud of stuff between us and the source.”
The researchers believe that, whether it’s near a black hole or a dense cloud of surrounding dust, the high activity of FRB 121102 compared to other FRBs may be caused in part to its particular environment.
Discovering more FRBs
While so few FRBs have been discovered to date, that’s set to change thanks to a Canadian telescope. And the researchers hope that more discoveries could reveal that repeating FRBs such as this one aren’t quite so rare..
The Canadian Hydrogen Intensity Mapping Experiment (CHIME), near Penticton, B.C., was unveiled in September 2017. It’s the largest telescope in the country and one of its primary goals will be to detect more of these FRBs, perhaps even as many as several a day.
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“I’m immensely excited about CHIME,” Hessels said. “If CHIME even finds one a day, by the end of the year, they’re going to find close to 100 or something like that, and if there’s no repeater within that sample, that’s going to be highly surprising.”
Though CHIME has had its “first light,” observations aren’t expected until the end of 2018.
“I think CHIME is going to be immensely important for figuring out what’s going on here,” Hessels said.