Due to this discovery, astronomers, including Jason Hessels and Kenzie Nimmo of the University of Amsterdam, now need to once again revise their ideas about the origins of these mysterious extragalactic signals. The result was announced at the meeting of the American Astronomical Society (AAS) in Honolulu, Hawaii, US and has now been published in Nature.

Mystery

The origin of these brief, highly intense bursts of radio waves is a mystery to astronomers. Although these bursts last only a thousandth of a second, hundreds of them have already been detected, but the exact source is known for only four FRBs. 

In 2016, it was discovered that one of these four localised sources repeated its bursts in an unpredictable manner. The radio bursts in question always came from the same small section of outer space. Since then, researchers have differentiated between FRBs for which just one burst is observed (non-repeating) and those for which multiple radio bursts have been recorded (repeating).

Extreme conditions

‘The multiple flashes that we witnessed in the first repeating FRB arose from very particular and extreme conditions inside a very tiny dwarf galaxy,’ says Benito Marcote from the Joint Institute for VLBI ERIC, lead author of the current study. ‘This discovery represented the first piece of the puzzle, but it also raised more questions than it solved, such as whether there was a fundamental difference between repeating and non-repeating FRBs. We have now localised a second repeating FRB, which challenges our previous ideas on what the source of these bursts could be.’

Op 19 June 2019, eight telescopes of the European VLBI Network (EVN) simultaneously observed a radio source known as FRB 180916.J0158+65. This source had already been discovered in 2018, using the CHIME telescope in Canada, and this enabled the team led by Marcote to observe FRB 180916.J0158+65 in very high resolution using the EVN. During five hours of observations, the researchers recorded four radio bursts, each of which lasted less than two thousandth of a second. The high resolution of the observations was achieved through the combination of radio telescopes located all over the world. Thanks to this technique, known as Very Long Baseline Interferometry (VLBI), they were able to establish that the radio bursts all had their origin in a section of space just seven light years across. This localisation is equivalent to someone on Earth being able to distinguish a single person standing on the Moon.

On the basis of this location, the team was able to make observations with one of the world’s biggest optical telescopes, the 8-metre Gemini North on Mauna Kea (Hawaii). By observing the environment of the source, the astronomers established that the radio bursts originated from a spiral galaxy (SDSS J015800.28+654253.0) that is 500 million light years away from Earth, and – more specifically – from an area in that galaxy where intensive star formation takes place. 

Totally different

‘The location found is totally different from the previously located repeating FRBs, but also different from all other previously studied FRBs,’ explains Kenzie Nimmo, PhD candidate at the University of Amsterdam. ‘The differences between repeating and non-repeating fast radio bursts are thus less clear and we now think that these events may not be linked to a particular type of galaxy or environment. It may be that FRBs are produced in a wide variety of locations across the universe and just require some specific conditions to be noticeable.’

Although the current research casts doubt on previous assumptions, this is the closest FRB that has been observed to date. This gives astronomers the chance to research this phenomenon in more detail than ever before.

‘We hope that continued studies will reveal the conditions that result in the production of these mysterious flashes. Our aim is to precisely localise more FRBs and, ultimately, to understand their origin,’ concludes Jason Hessels, corresponding author on the study, of the Netherlands Institute for Radio Astronomy (ASTRON) and the University of Amsterdam.

Publication

Marcote, B., Nimmo, K., Hessels, J.W.T., et al. 2020. ‘A repeating fast radio burst source localised to a nearby spiral galaxy’, Nature: https://doi.org/10.1038/s41586-019-1866-z