Astronomers baffled by mysterious radio signals coming from the center of the Milky Way

Astronomers discovered a mysterious signal coming from the center of our galaxy that "fit no currently understood pattern of variable radio source and could suggest a new class of stellar object," a press statement from the University of Sydney reveals.

At first, the scientists believed the signal might be coming from a pulsar — a type of star that spins at incredibly high speeds — or a star that was emitting large solar flares. On closer inspection, they found that the signals from the newly-discovered source don't match what we expect from those types of stars. They detailed their new findings in a paper published in the Astrophysical Journal.

"The strangest property of this new signal is that it is has a very high polarization. This means its light oscillates in only one direction, but that direction rotates with time," Ziteng Wang, lead author of the new study and a Ph.D. student in the School of Physics at the University of Sydney, explained in the statement. "The brightness of the object also varies dramatically, by a factor of 100, and the signal switches on and off apparently at random. We've never seen anything like it."

Wang and a group of international scientists discovered the object using CSIRO's ASKAP radio telescope in Western Australia. Follow-up observations were later made with the South African Radio Astronomy Observatory's MeerKAT telescope. The team had been searching the skies looking for unusual new space objects as part of a project known as variables and slow transients (VASTs). "Looking towards the center of the galaxy, we found ASKAP J173608.2-321635, named after its coordinates," said Wang's Ph.D. supervisor Professor Tara Murphy. "This object was unique in that it started out invisible, became bright, faded away, and then reappeared. This behavior was extraordinary."

Over a period of nine months in 2020, the team detected six radio signals from the source. However, when they tried to detect the object in visual light, they were surprised to find nothing. Though the astronomers cannot currently categorize the strange radio signal source, Wang's co-supervisor, Professor David Kaplan from the University of Wisconsin-Milwaukee, said there are "some parallels with another emerging class of mysterious objects known as galactic center radio transients, including one dubbed the 'cosmic burper'." Radio transients, with their short bursts of radio signals, are often signals for unusual astronomical events. In September, for example, astronomers from Caltech revealed their findings on radio transient signals that came from a black hole prematurely triggered a star to go supernova.

Next, the astronomers behind the discovery of the ASKAP J173608.2-321635 radio signal hope that more follow-up observations will shed light on the mysterious source. "Within the next decade, the transcontinental Square Kilometer Array (SKA) radio telescope will come online. It will be able to make sensitive maps of the sky every day," Professor Murphy explained. That new telescope may help to uncover the mystery, and it may also open the scientific community's eyes to a whole host of new mysteries lying in wait in the cosmos.

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