Since 2022, astronomers have been tracking extremely unusual bursts of radio emission, repeating at precisely defined intervals ranging from minutes to hours. Some last for over 30 years, while others fade after just a couple of days. To date, scientists have discovered about a dozen such sources, further deepening the mystery and generating numerous speculations about their possible origins.
In an effort to better understand these "long-period radio transients," an international team of scientists focused on ASKAP J1745, a highly polarized repeating radio burst first discovered 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 flash across a wide spectrum of light, including X-rays and radio waves, allowing them to figure out once and for all what was behind the phenomenon.
«"The famous Rosetta Stone, which carries the same message in three forms of writing, once helped scientists decipher ancient Egyptian hieroglyphs," wrote co-author and University of Sydney astrophysics PhD student Covey Rose in an article for The Conversation . "Similarly, this additional information we discovered about ASKAP J1745 will help astronomers better understand the mystery of all long-period transient phenomena.".
They found that long-period transients are likely not caused by pulsars—the rotating, highly charged remnants of dead stars—a theory that has become popular among researchers. This is because they repeat much more slowly than the average pulsar, which Rose claims repeats every few seconds.
The team concluded that ASKAP J1745 is likely a "catastrophic variable" star, or a system consisting of a pair of stars, one of which is a white dwarf—the dense stellar core left behind 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 absorbing material from the other star, a process that generates heat and, consequently, emits X-rays.
On the other hand, pulsed radio emission "is typically caused by the interaction of energetic particles with strong magnetic fields," Rose explains. "Here we have the perfect combination: two stars with strong magnetic fields (typically thousands of times stronger than an MRI machine) and charged particles moving toward the white dwarf from the other star.".
«"The simultaneous radio and X-ray observations provide unprecedented insight into how magnetic fields, accretion, and orbital motion interact, revealing behavior we have never seen before in a cataclysmic variable star," co-author Nanda Rea, a researcher at the Institute of Space Research of Catalonia, said in a statement.
In short, the obtained results shed light on the possible origin story of other long-period transient objects, and ASKAP J1745 acts as a decipherable Rosetta Stone.
«"We have spectroscopically confirmed that [ASKAP J1745] is an accreting cataclysmic variable, identified by its characteristic optical emission lines and ongoing X-ray outburst," the research team concluded in their paper. "Our results strengthen the connection between at least some LPT stars and white dwarf binaries.".
However, researchers still have much work to do to fully understand this strange phenomenon. First, the team cannot rule out that ASKAP J1745, which remains difficult to identify, is unique in its short-lived signals.
Still, it's an exciting first piece of the puzzle, and the team hopes to discover more signals as they investigate.
«"Each new discovery helps us piece together the big picture," Rose explained in a statement. "We're just beginning to understand this new class of cosmic events.".
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