Artist’s conception of the radio cluster. Image: University of Sydney
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Scientists have discovered a new cluster of unknown radio waves emanating from our galaxy’s center. According to scientists, the signals don’t line up with any known space object.
As detailed in a new paper published on Tuesday in the American Astronomical Society, researchers from the University of Sydney located a light formation at the center of the Milky Way six times between January and September of 2020. Each time it was a different size, polarized every time, meaning it rotating in a corkscrew pattern at a constant rate. All of this points to the possibility that this is a new class of object in space, such as a new type of star.
“It seems different to all types of astronomical objects we know, it may be a new type of object,” said Ziteng Wang, lead author of the study and a PhD student in the School of Physics at the University of Sydney in an email to Motherboard. “If this source is an example of a previously undiscovered class of object, it would be interesting to study these types of sources to further understand their origin.”
The team promptly named the cluster of signals ASKAP J173608.2−321635, a nod to the object’s coordinates in space and the telescope Wang and his team used: the Australian Square Kilometre Array Pathfinder Variables and Slow Transients (ASKAP VAST). With 36 dish antennas, the device, located in western Australia, uses high survey speeds designed to identify a wide variety of radio waves, ideal for picking up an object with waves at varying frequencies like the one Wang and his team identified.
“Our eye cannot distinguish between circularly polarized light and unpolarised one, but ASKAP has the equivalent of polaroid sunglasses to filter it out,” Wang said. “These kinds of sources are really rare, usually we only found ten out of thousands of sources polarized in one observation.”
The researchers also used the South African MeerKAT telescope, with 64 antennas, to identify the signal once they’d spotted it via the ASKAP. Working at a slightly different frequency and higher capability to detect pulsing radio waves, the second device gave the researchers a second look at the signal—this was crucial to landing on a few possible explanations for what the object could be i, Wang says.
“We started the MeerKAT observation from 2020 November, and we detected nothing until February, 2021,” Wang said. “Without another detection, it would be hard to know further details of the signal. We were really excited at that time.”
The images are unlike anything known to the scientific community, and, in fact, Wang and his team were unable to settle on one precise idea of what they could be.
The object could be one of a number of things, they write in the paper. It could be low-mass, or low-brightness star, a pulsar, a magnetar, or a Galactic Center Radio Transient, which is a catch-all term for bursts of radio activity from the galaxy’s center without a settled explanation.
Yet, none of these hypotheses quite aligns with what Wang and his team saw in the star: It lacks the infrared wavelengths of a low-mass star, the regular pulsations of a pulsar, and the x-ray waves of a magnetar. It could be called a GCRT, but those “are still a mystery,” Wang says. “We don’t even know if all GCRTs share a common origin, it is hard to say.”
Though still uncertain, the authors believe the star could represent a new class of galactic objects only discoverable through radio imaging surveys, which specifically capture radio waves. If true, it could open up a new field of astronomy, or a new segment of the Milky Way, for research.
“We need to do further investigations,” Wang said. “We might be able to use this kind of source as a clue to research something exciting, such as the expansion of the universe, fate of stars.”