Astronomers have spotted a star acting unlike any other ever observed, that is unleashing a curious combination of radio waves and X-rays every 44 minutes, pegging it as an exotic member of a class of celestial objects first identified only three years ago. It is located in the Milky Way galaxy about 15,000 light-years from Earth in the direction of the constellation Scutum.
The researchers said it belongs to a class of objects called “long-period radio transients,” known for bright bursts of radio waves that appear every few minutes to several hours.
“What these objects are and how they generate their unusual signals remain a mystery,” said Curtin University astronomer Ziteng Wang, lead author of the study published this week in the journal Nature.
Photo: NASA/Chandra/Spitzer/MeerKat via AP
In the new study, the researchers used data from NASA’s orbiting Chandra X-ray Observatory, the Australian Square Kilometre Array Pathfinder telescope in Australia and other telescopes.
While the emission of radio waves from the object is similar to the approximately 10 other known examples of this class, it is the only one sending out X-rays, said astrophysicist and study coauthor Nanda Rea of the Institute of Space Sciences in Barcelona.
The researchers have some hypotheses about the nature of this star, including that it might be a magnetar — a spinning neutron star with an extreme magnetic field — or a white dwarf, a highly compact stellar ember, with a close and quick orbit around a small companion star.
“However, neither of them could explain all observational features we saw,” Wang said.
Stars with up to eight times the mass of our sun appear destined to end up as a white dwarf. They eventually burn up all the hydrogen they use as fuel. Gravity then causes them to collapse and blow off their outer layers, eventually leaving behind a compact core roughly the diameter of Earth — the white dwarf.
The observed radio waves could have been generated by the interaction between the white dwarf and the hypothesized companion star, the researchers said.
“The radio brightness of the object varies a lot. We saw no radio emission from the object before November 2023. And in February 2024, we saw it became extremely bright. Fewer than 30 objects in the sky have ever reached such brightness in radio waves. Remarkably, at the same time, we also detected X-ray pulses from the object. We can still detect it in radio, but much fainter,” Wang said.
Wang said it is thrilling to see a new type of behavior for stars.
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