Radio Signals from the Center of the Milky Way Pose Mystery - Science Club

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Radio Signals from the Center of the Milky Way Pose Mystery

 Radio signals from the center of the Milky Way don’t seem to act like anything astronomers have ever seen before - so, what is it?

Astronomers participating in the ASKAP survey have spotted a unusual radio signal coming from the direction of the center of the Milky Way. These flashes of radio emissions are unlike anything astronomers have ever seen before.

This odd signal — dubbed ASKAP J173608.2–321635 — varies 100 times in intensity between its brightest and dimmest moments. And, these radio signals from the center of the Milky Way seem to “switch on and off” at — apparently — random intervals. This behavior might suggest astronomers are glimpsing a previously-unknown type of object.

“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,” explains Professor Tara Murphy of the Sydney Institute for Astronomy and the School of Physics.

Tara Murphy interview on Astronomy News with The Cosmic Companion sneak preview. Full interview drops 2 November. Video credit: The Cosmic Companion

Join us on Astronomy News with The Cosmic Companion on 2 November, when we talk with Tara Murphy about this discovery!

Now You See It, Now You Don’t…

The 36 dishes of the ASKAP network of radio telescopes each contain a cutting-edge radio ‘camera’ called a phased array feed receiver. Together, these instruments produce more than 100 trillion bits of data every second — more than all the internet traffic in Australia.

Following six detections over nine months in 2020 using the ASKAP network of radio telescopes in Western Australia, astronomers searched for the target in visible light utilizing visible-light telescopes — and found nothing. Observations using the Parkes radio telescope to confirm these odd radio signals from the center of the Milky Way also turned up empty.

“‘It’s quiet. No cars. No birds. Nothing.’ ‘No radio waves,’ said the Doctor. ‘Not even Radio Four.’ ‘You can hear radio waves?’ ‘Of course not. Nobody can hear radio waves,’ he said unconvincingly.” — Neil Gaiman

Turning to the more-sensitive MeerKAT radio telescope, researchers finally spotted the signal once more. But, the signal which lasted weeks in the initial observations faded out after only a day the second time around.

“We monitored the source with the MeerKAT telescope from 2020 November to 2021 February on a 2–4 week cadence. The source was not detected with MeerKAT before 2021 February 7,” researchers describe in The Astrophysical Journal.

OK, Suppose It’s… Well, It’s Not THAT…

Puzzling out the nature of these bizarre radio signals from the center of the galaxy turned out to be a puzzle astronomers are still trying to piece together.

“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,” Ziteng Wang, PhD student in the School of Physics at the University of Sydney, and lead author of a new study on the discovery, describes.

The light from ASKAP J173608.2–321635 is also oddly polarized, as seen in this visualization. Video credit: The University of Sydney.

And, just as light can be polarized by reflecting off a puddle or snow (hence the need for polarizing sunglasses), radio signals from ASKAP J173608.2–321635 are also highly-polarized.

“The strangest property of this new signal is that it is has a very high polarisation. This means its light oscillates in only one direction, but that direction rotates with time,” Wang explains.

Researchers tested several ideas about the nature of this odd signal, finding ASKAP J173608.2–321635 could not be explained as pairing of a low-mass star and a body not quite large enough to be a star. A suggestion that signal is scattered light from a pulsar was also found not to match observations.

“The information we do have has some parallels with another emerging class of mysterious objects known as Galactic Centre Radio Transients, including one dubbed the ‘cosmic burper’. While our new object, ASKAP J173608.2–321635, does share some properties with GCRTs there are also differences. And we don’t really understand those sources, anyway, so this adds to the mystery,” describes Professor David Kaplan from the University of Wisconsin-Milwaukee.

This mystery — and others like it — may be answered as future instruments, such as the Square Kilometre Array (SKA), begin their search of the Cosmos. And, these new eyes on the sky are also certain to create even more mysteries about the Universe we all call home.

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

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