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A depiction of a white dwarf star drawing matter from its stellar companion. This process might account for enigmatic radio energy bursts that have perplexed astronomers.(Image credit: Carl Knox (OzGrav/Swinburne) and Dr. Joshua Preston Pritchard (CSIRO))Share this article 0Join the conversationFollow usAdd us as a preferred source on GoogleSubscribe to our newsletter
A pair of orbiting stars could serve as a model for deciphering puzzling radio signals emanating from space, according to recent findings.
Long-period transients have mystified radio astronomers since their initial detection in 2022. These celestial bodies emit strong bursts of radiation at intervals of minutes to hours, with each emission lasting only a few seconds. They are significantly slower than phenomena like fast radio bursts, which are potent energy pulses that flash for mere milliseconds.
Numerous hypotheses exist regarding the nature and powering mechanisms of these transients. Possibilities include slowly rotating stellar remnants (pulsars) or the condensed cores of collapsed stars (white dwarfs). Prior research on other long-period transients has suggested they might be white dwarfs engaged in a slow orbital dance with another entity.
A recent study, published on June 1 in the journal Nature Astronomy, proposes that a newly identified long-period transient, designated ASKAP J1745−5051, is a type of stellar system known as a magnetic cataclysmic variable. This classification refers to a binary system where a white dwarf is actively siphoning material from its companion star. This marks the first confirmation of a long-period transient within an accreting system, where matter transfer between celestial bodies occurs.
This discovery is considered “a Rosetta Stone to help us decipher the missing bits of information in other long-period transients, both in the dozen or so that we’ve discovered, and the new ones that we’re going to keep discovering,” stated Kovi Rose, the lead author of the study and a doctoral candidate at the University of Sydney, in comments to Live Science. (The Rosetta Stone is an ancient artifact that aided in the translation of Egyptian hieroglyphics.)
Something unexplained
Rose examined over 3 million radio wave sources using the Australian SKA Pathfinder telescope (ASKAP), narrowing down the selection to 100 sources exhibiting circularly polarized light, indicating a corkscrew-like propagation towards Earth.
Among these candidates, two objects initially defied immediate classification. The first was identified as an ultra-cool brown dwarf, possessing a temperature comparable to a pizza oven. The second was ASKAP J1745−5051. It presented as “something we couldn’t explain, and when we eventually managed to explain it, it was more interesting than we could have hoped for,” Rose remarked.
Utilizing data from multiple radio telescopes, in addition to optical and X-ray observations, Rose and his colleagues demonstrated that the object generates powerful bursts of radiation in both radio waves and X-rays every 1.3 hours. This object is situated more than a thousand light-years away.
The ASKAP radio telescope (foreground) viewed over a radio representation of magnetic fields in the night sky (background). This array was crucial in decoding the radio signals observed in the new investigation.
(Image credit: CSIRO/Alec Thomson et al./Alex Cherney/Sam Moorfield)
“You’d observe these distinct pairs of pulses – pulse-pulse, pulse-pulse, pulse-pulse, and then it would cease,” Rose elaborated.
However, several peculiar characteristics of the system have aided researchers in uncovering the source of the periodic signals.
Notably, the radio waves and X-rays peaked at different times, indicating their origin from distinct regions within the system, Rose noted. The team proposed that the radio emissions are generated when the magnetic fields of the stars interact with the material being stripped from the smaller star. This material, heated by the white dwarf, subsequently emits X-rays.
Further examination revealed emissions consistent with the presence of helium and hydrogen, which exhibited frequency drift. “The wavelengths would shift towards higher frequencies and then revert to lower frequencies, a definitive indicator of a binary system,” Rose stated. This was a “smoking gun,” confirming the presence of two stars orbiting each other.
“This paper establishes a strong link for at least some long-period transients with white dwarf binary systems,” commented Marcin Glowacki, an astronomer at the Royal Observatory, Edinburgh, University of Edinburgh, who was not involved in the research, via email to Live Science. “We are also observing novel behavior in this [transient], previously seen in only one other [transient], with emissions drifting up and down in frequency. This behavior can offer significant insights into the immediate plasma or accretion environment” of this long-period transient.
He expressed surprise, however, at the identification of ASKAP J1745−5051 as a cataclysmic variable. “As the paper indicates, 50 other cataclysmic variables have been observed to produce radio emissions, but none with the periodic behavior observed here, and they are typically much fainter.”
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Patrick Woudt, an astronomer at the University of Cape Town, South Africa, specializing in cataclysmic variables and unaffiliated with the study, told Live Science via email that ASKAP J1745-5051 serves as a crucial link between long-period transients and cataclysmic variables.
“ASKAP J1745-5051 is several orders of magnitude brighter than the compact variables observed at radio frequencies, so what makes ASKAP J1745-5051 so unique among the magnetic CVs?” he inquired. “That is a highly intriguing question that warrants further investigation with future observations, not only at radio frequencies but also at UV, optical, and X-ray wavelengths.”
Looking ahead, Rose intends to explore the X-ray characteristics of ASKAP J1745−5051 and further define the system to uncover any remaining secrets it holds.
Sourse: www.livescience.com
