Milky Way radio signals visualised by The University of Sydney
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The unexpected discovery was made by researchers at the University of Sydney, using a powerful radio telescope in Western Australia. Although astronomers frequently detect unusual phenomena coming from the heart of the galaxy, the Sydney researchers have so far failed to explain their latest find. The radio waves picked up by the Australian SKA Pathfinder Telescope (ASKAP) do not appear to fit any known source of radio signals in space.
The researchers are now determined to discover what exactly is going on in the galactic centre, which is about 26,000 light-years from Earth.
According to international student Ziteng Wang, who made the discovery, the signal may indicate the presence of a new class of stellar objects.
He said: “The strangest property of this new signal is that it has a very high polarisation.
“This means its light oscillates in only one direction, but that direction rotates with time.”
Mr Wang is a PhD student at the university’s School of Physics and the lead author of a new study describing the phenomenon.
He added: “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.”
His discovery was published this week in the peer-reviewed Astrophysical Journal.
Stars of various kinds emit light spanning the breadth of the electromagnetic spectrum.
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The spectrum covers all types of electromagnetic radiation, which includes visible light, X-rays, ultraviolet and radio waves, among others.
Stellar bodies like pulsars, supernovas, fast radio bursts and flaring stars all have varying brightnesses.
But so far, none of these objects have been able to explain the mystery signal.
Mr Wang said: “At first we thought it could be a pulsar – a very dense type of spinning dead star – or else 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.”
Mr Wang’s PhD supervisor, Professor Tara Murphy, added: “We have been surveying the sky with ASKAP to find unusual new objects with a project known as Variables and Slow Transients (VAST), throughout 2020 and 2021.
“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.”
After originally detecting the signal with ASKAP, the radio waves were confirmed using the South African Radio Astronomy Observatory’s MeerKAT telescope.
In total, the scientists detected six signals from the mystery source over a nine-month period in 2020.
Professor Murphy said: “Within the next decade, the transcontinental Square Kilometre Array (SKA) radio telescope will come online.
“It will be able to make sensitive maps of the sky every day.
“We expect the power of this telescope will help us solve mysteries such as this latest discovery, but it will also open vast new swathes of the cosmos to exploration in the radio spectrum.”
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