Since 2022, astronomers have been tracking highly unusual bursts of radio emissions that repeat at precise intervals, ranging from a few minutes to several hours. Some pulse for more than 30 years, while others wink out after only a couple of days. Scientists have discovered of a dozen of these sources so far, adding to the mystery and prompting plenty of speculation over their possible origins.
In an effort to better understand these “long-period radio transients,” an international team of scientists honed in on ASKAP J1745, a highly polarized repeating radio burst first detected by the Australian Square Kilometre Array Pathfinder (ASKAP) telescope.
As detailed in a new paper published in the journal Nature Astronomy, several different telescopes observed this burst across a broad spectrum of light, including X-ray and radio waves, giving them an opportunity to figure out what’s behind the phenomenon once and for all.
“Bearing the same message in three forms of writing, the famous Rosetta stone once helped scholars decipher ancient Egyptian hieroglyphs,” wrote coauthor and University of Sydney Astrophysics PhD Candidate Kovi Rose in a writeup for The Conversation. “Similarly, this extra information we found about ASKAP J1745 will help astronomers better understand the mystery of all long-period transients.”
They found that long-period transients likely aren’t caused by pulsars, the spinning and highly energized remains of dead stars, which had emerged as a popular theory among researchers. That’s because they repeat far slower than the average pulsar, which repeats every few seconds, as Rose argues.
The team concluded that ASKAP J1745 is likely a “cataclysmic variable” star, or a system made up of a pair of stars, with one of them being a white dwarf — the dense stellar core left over after a relatively low-mass star has exhausted its fuel. Rose and his colleagues believe the radio burst may be caused by the white dwarf accreting material from the other star, a process that generates heat and thereby releases X-ray light.
The pulsed radio light, on the other hand, is “typically caused by energetic particles interacting with strong magnetic fields,” as Rose explains. “Here, we have the perfect combination: two stars with strong magnetic fields (typically thousands of times stronger than an MRI machine), with charged particles flowing towards the white dwarf from the other star.”
“The simultaneous radio and X-ray observations provide an unprecedented view of how magnetic fields, accretion, and orbital motion interact, revealing behavior we had never before observed in a cataclysmic variable,” said coauthor and Institute of Space Studies of Catalonia researcher Nanda Rea in a statement.
In short, the findings shed light on the possible origin story of other long-period transients, with ASKAP J1745 acting as the deciphering Rosetta stone.
“We have spectroscopically confirmed [ASKAP J1745] as an accreting cataclysmic variable, identified through characteristic optical emission lines and an ongoing X-ray outburst,” the team concluded in its paper. “Our results strengthen the link between at least some LPTs and white dwarf binaries.”
Yet the researchers still have plenty of more work left to do to get a full picture of the odd phenomenon. For one, the team can’t rule out that ASKAP J1745, which remains hard to pin down, is unique when it comes to these transient signals.
Nonetheless, it’s an exciting first piece of the puzzle, and the team is hopeful to catch more signals in the act.
“Each new discovery is helping us piece together the bigger picture,” Rose explained in a statement. “We’re only just beginning to understand this new class of cosmic events.”
More on radio bursts: Astronomers Intrigued by 25 Mysterious Repeating Radio Signals From Deep Space
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