A Canadian radio telescope discovered 535 fast radio bursts in one go, quadrupling the known number of these brief, very powerful events. The long-awaited findings reveal that these perplexing events may be divided into two types: one-time bursts and recurrent bursts that continue at least ten times longer on average.
Fast radio bursts could be the outcome of at least two different astrophysical occurrences, according to the research. Kiyoshi Masui, an astrophysicist at the Massachusetts Institute of Technology in Cambridge, adds, “I think this just nails it that there is a difference.”
The radio astronomy community is in a tizzy due to an overnight increase in available data. Laura Spitler, an astronomer at the Max Planck Institute for Radio Astronomy in Bonn, Germany, co-discovered the first repeating burst in 2016 using the now-collapsed Arecibo observatory in Puerto Rico, says, “All my Slack channels were full of people talking about the publications.”
Between 2018 and 2019, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) recorded the events in its first year of operation. On June 9, the team presented their findings at a virtual meeting of the American Astronomical Society and released four preprints to the arXiv online repository.
ONE-OFFS AND REPEATERS
CHIME, a telescope with no moving parts, is located near Penticton, British Columbia. It consists of four 100-meter-long half-pipe antennas. It only sees a limited strip of sky above it at any given time. The telescope, on the other hand, scans the sky as the Earth revolves, and digital processing chips collect the data to create an image.
CHIME was designed to map the distribution of matter in the Universe, but a complicated kit of extra electronics was added to the design so that it could also detect quick radio bursts. Many in the field had doubts about the telescope’s ability to detect the bursts, according to Spitler, but the current announcement has proven them wrong. Spitler says, “They’re meeting their prediction.” “It’s quite impressive.”
Although the reason for quick radio bursts is still unknown, the CHIME findings seem to support the assumption that there are at least two types. Sixty-one of the 535 discovered were ‘repeaters,’ meaning they emanated from 18 different sites that had previously been seen releasing bursts. The duration of the two types of bursts differs, with one-off events being substantially shorter. Repeaters also have a significantly narrower radio frequency spectrum than one-off bursts.
Spitler says, “It’s by far the most persuasive proof that there are two populations.”
Until now, the evidence was weak: some astronomers claimed that non-repeating bursts could simply have been repeaters that had not been monitored long enough to burst again. “That doesn’t rule out the possibility that the phenomenon is different,” Masui says.
Fast radio bursts are usually detected after a second or more has passed. However, as signals travel over millions of light-years of space, intergalactic matter tends to disperse radio waves across the spectrum, resulting in a misleadingly long duration. As a result, when compared to higher-frequency waves, lower-frequency waves can arrive at Earth with a delay of several seconds. Researchers have calculated that the emission of a radio burst lasts only milliseconds at the source. During that time, a burst’s source can produce 500 million times more energy than the Sun in the same period.
The size of this wavelength dispersion gives a rough idea of how far the waves had to travel. Except for one event that happened in the Milky Way, all bursts have been shown to originate in other galaxies.
The origin of the bursts appeared to be uniformly distributed over the sky, according to CHIME researchers. Only a few could be linked to a certain galaxy.
THEORIES OF ORIGIN
Researchers have been watching some of the sky locations that have produced bursts in past in recent years, and they’ve observed them recur with regularity in some cases. Spitler and her partners identified a ‘repeater’ in 2016 that has activity cycles that span a day or so, producing numerous bursts per hour, and repeats every 160 days.
This constant repetition may provide some insight into what is triggering the bursts. Repeaters could form when a strongly magnetic neutron star loops around an ordinary star in an elongated orbit, according to Spitler. Bursts could emerge from the neutron star’s magnetic field scattering the very energetic stellar wind as it comes closer to its companion regularly.
Non-repeaters, on the other hand, could be the outcome of catastrophic events like neutron star collisions or magnetic storms in young neutron stars known as magnetars. A known magnetar was linked to the Milky Way occurrence. The discovery of a burst from a ‘globular cluster’ in the galaxy M81, published last month, has put doubt on the magnetar idea. Magnetars are thought to be rare to be found in globular clusters, which are dense groups of very old stars.
Researchers were taken aback when the first fast radio burst was discovered in 2007, and just a few were recognized for many years, according to Masui. Theorists came up with a slew of theories, and it was a running joke that the ideas outweighed the actual happenings. “I don’t think theories will catch up with us,” he adds now that CHIME has reversed the trend. And this is just the beginning: the team has proceeded to discover many more fast radio bursts since those results were gathered and will continue to publish them for years to come.