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New detections of radio waves from a repeating fast radio burst have revealed an astonishingly potent magnetic field in the source鈥檚 environment, indicating that it is situated near a massive black hole or within a nebula of unprecedented power.

The findings by an international team of astronomers, including Victoria Kaspi and Shriharsh Tendulkar of McGill University, appear in the January 11 edition of Nature and are highlighted on the cover of the journal.

A year ago, the astronomers pinpointed the location of the enigmatic fast radio burst (FRB) source named FRB 121102 and reported that it lies in a star-forming region of a dwarf galaxy more than 3 billion light years from Earth. The vast distance to the source implies that it releases an enormous amount of energy in each burst -- roughly as much energy in a single millisecond as the Sun releases in an entire day.听

Now, using data from the Arecibo Observatory (Puerto Rico) and the Green Bank Telescope (West Virginia), the researchers have shown that the radio bursts from FRB121102 are highly polarized. The behavior of this polarized emission enables scientists to probe the source鈥檚 environment in a new way.

Twisted polarization

When polarized radio waves pass through a region with a magnetic field, the polarization gets ``twisted鈥欌�� by an effect known as Faraday rotation: the stronger the magnetic field, the greater the twisting. The amount of twisting observed in FRB 121102鈥檚 radio bursts is among the largest ever measured in a radio source, leading the researchers to conclude that the bursts are passing through an extraordinarily strong magnetic field in a dense plasma.

"I could not believe my eyes when my colleagues emailed the results around,鈥� says Kaspi, who is a professor of physics at McGill and director of the McGill Space Institute. 鈥淭his sort of enormous Faraday rotation is extremely rare. Once we digested it, we realized it was a huge clue about where this bizarre source resides."

One possible explanation for the hugely magnetized environment is that FRB 121102 is located close to a massive black hole in its host galaxy.听 Such highly magnetized plasmas have so far been seen only near the center of the Milky Way, which has its own massive black hole. But the authors also speculate that the twisting of the radio bursts could be explained if FRB 121102 is located in a powerful nebula (an interstellar cloud of gas and dust) or amid the remains of a dead star.

FRBs are a recently discovered class of transient astrophysical events, originating from deep in extragalactic space. Their physical nature remains a mystery. FRB 121102 is the only known repeating FRB, and this has also raised the question of whether it has a different origin compared to the apparently non-repeating FRBs. 鈥淔RB 121102 was already unique because of its repetition; now the huge Faraday rotation we have observed singles it out yet again.听 We鈥檙e curious as to whether these two unique aspects are linked,鈥� says Daniele Michilli, PhD candidate at the University of Amsterdam and ASTRON (Netherlands Institute for Radio Astronomy).

New telescopes could provide answers

With a number of wide-field radio telescopes now coming online, more such sources are expected to be discovered in the coming year, and astronomers are poised to answer more fundamental questions about FRBs.

"The in Penticton, British Columbia, should be an excellent instrument for detecting fast radio bursts and studying their polarization properties,鈥� says Shriharsh Tendulkar, postdoctoral researcher at the McGill Space Institute. 鈥淲hen it comes online in 2018, it should be capable of detecting between a few and a few dozen FRBs every day."
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鈥淎n extreme magneto-ionic environment associated with fast radio burst source FRB 121102,鈥澨� D. Michilli et al., Nature, 11 January 2018. doi:10.1038/nature25149

Support for the McGill researchers was provided by the Lorne Trottier Chair in Astrophysics & Cosmology, the Canada Research Chairs program, the Natural Sciences and Research Council of Canada, the Canadian Institute for Advanced Research, and the FRQNT Centre de Recherche en Astrophysique du Qu茅bec.

I惭础骋贰:听The 305-metre Arecibo telescope, in Puerto Rico, and its suspended support听platform of radio receivers is shown amid a starry night.听 A flash from the Fast Radio Burst source FRB 121102 is seen: originating beyond the Milky Way, from deep in extragalactic space.听CREDITS: Image design: Danielle Futselaar - Photo usage: Brian P. Irwin / Dennis van de Water / Shutterstock.com

Background video on Fast Radio Bursts and the CHIME telescope:

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Contacts:

Prof. Victoria Kaspi, McGill University / McGill Space Institute
vkaspi [at] physics.mcgill.ca

Dr. Shriharsh Tendulkar, McGill Space Institute / McGill University
shriharsh [at] physics.mcgill.ca

Chris Chipello, Media Relations, McGill University
514-398-4201
christopher.chipello [at] mcgill.ca

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