An area near the centre of the Milky Way has been sending out strange radio waves, baffling astronomers.
The waves may suggest a new type of stellar object, but currently fits no recognisable pattern of variable radio source.
Across the electromagnetic spectrum, fluctuating light is emitted by many types of stars. Radio astronomy has since made immense advances through the studying of variable or transient objects in radio waves. However, the brightness of astronomical objects varies, from pulsars, supernovae, flaring stars and fast radio bursts, EurekAlert! reports.
Lead author of the new study and PhD students in the School of Physics at the University of Sydney, Ziteng Wang, noted that the ‘strangest property’ of the ‘new signal’ was its ‘very high polarisation’. ‘This means its light oscillates in only one direction, but that direction rotates with time,’ he explained.
Due to the brightness of it varying ‘dramatically’, and despite six radio signals being detected over nine months in 2020, Wang noted how the team had not seen ‘anything like it’. According to Wang, the brightness was changing ‘by a factor of 100’, and the signal was turning ‘on and off apparently at random’.
While he had first thought it may be a pulsar, which is a ‘very dense type of spinning dead star’ or ‘a type of star that emits huge solar flares’, the ‘signals from this new source don’t match what we expect from these types of celestial objects,’ Wang explained.
Throughout 2020 and 2021, Wang’s supervisor, Professor Tara Murphy, noted how the team had been ‘surveying the sky with ASKAP to find unusual new objects with a project known as Variables and Slow Transients (VAST)’.
Looking towards the centre of the Galaxy, we found ASKAP J173608.2-321635, named after its coordinates. This object was unique in that it started out invisible, became bright, faded away and then reappeared. This behaviour was extraordinary.
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.
While Murphy noted how the ‘signal returned’, when it did, 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,’ she said.
The astronomers have subsequently not gotten to the bottom of identifying the mysterious object.
Although, Professor David Kaplan, Wang’s co-supervisor, noted the ‘parallels with another emerging class of mysterious objects known as Galactic Centre Radio Transients, including one dubbed the “cosmic burper”.’
The new object was titled, ASKAP J173608.2-321635, and while it shared ‘some properties with GCRTs’, it still remains quite a mystery.
Today, October 12, the discovery was published in the Astrophysical Journal. It is hoped that more ‘sensitive maps of the sky’ will be able to be made daily within the ‘next decade’ as a result of the transcontinental Square Kilometre Array (SKA) radio telescope coming online.
Professor Murphy concluded that the power of the telescope will ‘help […] solve mysteries such as this latest discovery, but […] will also open vast new swathes of the cosmos to exploration in the radio spectrum’.
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