A mysterious rhythm coming from another galaxy
For about four days, the radio waves would arrive at random. Then, for the next 12, nothing.
Then, another four days of haphazard pulses. Followed by another 12 days of silence.
The pattern — the well-defined swings from frenzy to stillness and back again — persisted like clockwork for more than a year.
Dongzi Li, a doctoral student at the University of Toronto, started tracking these signals in 2019. She works on a Canadian-led project, CHIME, that studies astrophysical phenomena called “fast radio bursts.” These invisible flashes, known as FRBS for short, reach Earth from all directions in space. They show up without warning and flash for a few milliseconds, matching the radiance of entire galaxies.
Astronomers don’t know what makes them, only that they can travel for millions, even billions, of years from their sources before reaching us. In the past decade, astronomers managed to detect about 100 of them before they vanished.
Li was monitoring FRBS, tracking their arrival times at a radio telescope in British Columbia, when she noticed that unusual pattern from one FRB source — four days on, 12 days off. (This is, perhaps, the purest definition of radio silence.)
The FRB, known by the bar-codeesque designation 180916.J0158+65, is the first to show this kind of regular cadence. Astronomers traced the source to a spiral galaxy about 500 million lightyears away, where it’s still going strong.
The paper on this discovery, published earlier this month, marked the end of formal observations in February. Like so many people this year, Li has spent most of her days at home, rarely venturing beyond the walls of her small apartment in Bonn, Germany, but the
Canadian observatory continues to scan the skies, catching the fleeting FRBS as little smudges of black against a plot of white noise. When Li and I spoke this week, she told me she’s still checking — and the rhythm is still there.
The discovery is an intriguing addition to a growing inventory of knowledge in a field whose earliest evidence was almost dismissed as a fluke. The first FRB was discovered in 2007, buried deep in archival data of a telescope in Australia, while astronomers were looking for another astrophysical phenomenon. The signal was thought to be a telescope artifact, a trick of light masquerading as a cosmic curiosity. And then similar signals started showing up in observations at other telescopes.
Astronomers accepted that they had detected a real event, but they still thought FRBS were one-offs. The flashes were so intense, even after crossing unfathomable distances in space, that whatever had produced them seemed unlikely to survive the cataclysm. But then astronomers found a repeater, a source of FRBS capable of erupting again and again, sometimes several times in less than a minute.
When astronomers managed to trace an FRB to its home galaxy for the first time, they found a small, lively galaxy, where new stars blinked into existence more than 100 times faster than in our own Milky Way. So FRBS must come from these kinds of environments, they thought. But then astronomers found that some FRBS originated in larger, mellower galaxies too.
“It seems like every time the scientific community converges on a possibility of what FRBS might be, some other observation happens that throws all these speculations out the window,” Kaitlyn Shin, an astrophysics graduate student at MIT who worked on the discovery of the pattern-bearing FRB, told me. “Now all the other theories going forward have to find a way to account for this periodicity.”
And not just from the FRB that Shin and Li’s team found, either; a different team reported this month the discovery of another signal that pulses in a much longer pattern — a 157-day cycle, with 90 days of bursts, followed by 67 days of silence. Many other FRB sources might also follow distinct rhythms, but telescopes just haven’t observed them long enough to spot the tempo.
The nature of the objects that produce FRBS remains a mystery, but astronomers are collecting clues.
This article was first published in The Atlantic. Read the full article on: www.irandailyonline.ir/news/270681.html