A Mystery Radio Signal From Deep Space Appears to Be Repeating a 16-Day Cycle

[www.newsweek.com]

Scientists say they have identified the first fast radio burst [FRB] which pulses with a regular pattern, casting new light on one of the universe's greatest mysteries.

FRBs are bright pulses of radio emissions—lasting milliseconds, or fractions of a millisecond—which appear to originate from far beyond our galaxy.

To date, researchers have uncovered more than 100 FRBs since they were first identified in 2007. However, the origin of these extremely energetic radio bursts remains unknown.

Most FRB sources emit a single one-off burst. But a minority—around 10—have been shown to repeat, although the bursts appear to be sporadic without a regular pattern.

However, a team of scientists led by Dongzi Li, an astrophysicist at the University of Toronto, have now found that one of the known FRB sources emits radio bursts with a distinctive repeating pattern.

The findings are described in a paper hosted on the pre-print server arXiv.org, so it is important to note that the results have not yet been subjected to review by experts in the field, unlike those published in scientific journals.

By analyzing data collected by the CHIME (Canadian Hydrogen Intensity Mapping Experiment) radio telescope in British Columbia, the team worked out that the source known as FRB 180916.J0158+65 emits radio bursts with a seemingly regular pattern based on a 16-day cycle.

As other recent research published in the journal Nature has revealed, the FRB in question lies in a star-forming region in the outskirts of a galaxy located around 500 million light-years from Earth—making it the closest known FRB to Earth.

According to the authors of the arXiv paper, the FRB produces several radio bursts per day for a period of four days, before falling silent for slightly more than 12 days. The overall cycle, therefore, lasts for just over 16 days.

In the study period—September 2018 to October 2019—the researchers observed that some cycles did not produce any detectable bursts. However, the FRB source would often produce multiple bursts, and these adhered to the pattern of the 16-day cycle.

"We conclude that this is the first detected periodicity of any kind in an FRB source," the team said in a paper published on the preprint server arXiv in late January. "The discovery of a 16.35-day periodicity in a repeating FRB source is an important clue to the nature of this object."

Despite the latest results, it it still not clear what the source of FRB 180916.J0158+65 is. Nevertheless, the latest results could could help to shed light on what is causing the mysterious radio bursts.

"This is very significant," Duncan Lorimer, an astrophysicist from West Virginia University in Morgantown who was not involved in the study, and co-discoverer of the first FRB, told ScienceNews. "It's potentially going to take us in an interesting direction to get to the bottom of these repeaters."

"There's nothing particularly special about this repeater," Lorimer said. "The fact that they detected periodicity on this one hints that other ones will have periodicity as well."

Even though scientists can't say what is producing FRB 180916.J0158+65, they think that something in its vicinity is likely modulating its bursts of activity. For example, a massive object such as a nearby black hole or a star, could be responsible for the unusual burst cycle, as could other phenomena such as stellar winds.

One study which was also published on arXiv.org on Wednesday even suggested that the 16-day cycle could be explained by a binary system containing a massive star and a neutron star—incredibly dense, compact objects that are left behind when massive stars explode as supernovae—Vice News reported.

It is also possible that the 16-day cycle that the researchers observed is intrinsic to the FRB itself. For example, some have suggested that a source of FRBs could be a type of highly magnetized neutron stars known as magnetars. However, this explanation does not coincide with the data that was collected.

They are very significant - this is the first time that we have direct evidence for a periodic phenomenon as an essential ingredient to repeating FRBs, and on what timescale that phenomenon needs to operate.

"I was surprised to see a periodicity in the outburst windows," Lorimer told Newsweek. "I think the result is really interesting in that regard. I was thinking more in terms of a periodicity in the arrival times of the pulses themselves. I think these new results hint at some sort of orbital phenomenon that is driving this behavior."