'We’ve never seen anything like it': Mysterious Milky Way radio waves baffle astronomers
Wednesday, 13 October 2021
Astronomers have detected unusual signals coming from the centre of the Milky Way, and are yet to piece together what's causing it.
According to researchers, the radio waves don’t fit any understood pattern of variable radio source and could suggest a new class of stellar object.
The astronomers shared their findings in a study published in The Astrophysical Journal.
In a University of Sydney press release, lead author Ziteng Wang said the strangest property of the new signal was that it has a very high polarisation, meaning its light oscillates in one direction, but that direction rotates with time.
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“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,” he said.
At that first, Wang said they thought the signals may have been from a pulsar – a very dense type of spinning dead star, or a type of star that emits huge solar flares.
“But the signals from this new source don’t match what we expect from these types of celestial objects,” he said.
Wang and an international team of experts discovered the object using the CSIRO's ASKAP radio telescope in Western Australia. Follow-up observations were made with the South African Radio Astronomy Observatory’s MeerKAT telescope.
The researchers named the object ASKAP J173608.2-321635, after its coordinates.
Professor Tara Murphy from the School of Physics and Sydney Institute for Astronomy, said this object was unique because it started out invisible, became bright, faded away and then reappeared.
“This behaviour was extraordinary,” she said.
After detecting six radio signals from the source over nine months in 2020, the astronomers tried to find the object in visual light, but couldn’t. They turned to the Parkes radio telescope but again couldn’t detect the source.
“We then tried the more sensitive MeerKAT radio telescope in South Africa. Because the signal was intermittent, we observed it for 15 minutes every few weeks, hoping that we would see it again,” Murphy said in the university statement.
“Luckily, the signal returned, but we found that the behaviour of the source was dramatically different – the source disappeared in a single day, even though it had lasted for weeks in our previous ASKAP observations.”
Despite this discovery, there are still a lot of unknowns regarding the transient radio source.
Professor David Kaplan, from the University of Wisconsin-Milwaukee, said there are some similarities with another emerging class of mysterious objects known as Galactic Centre Radio Transients, but there are also differences.
“And we don’t really understand those sources, anyway, so this adds to the mystery.”
The scientists plan to continue observing the object with the aim of piecing together the puzzle of what it might be.
It's not the first time unusual signals have been detected in space. Last year, scientists in Canada published some research on a series of fast radio bursts (FRBs) which are bright, millisecond-duration radio signals originating from deep in space.
The powerful, high energy bursts are some of the most enigmatic phenomena in astronomy.