Artist's impression showing the radio signal ASKAP J173608.2-321635 reaching Earth. Credit: Sebastian Zentilomo/University of Sydney
Astronomers discovered unusual signals that came from the center of the Milky Way. These radio waves could indicate a new class or stellar object, as they do not fit any known pattern of variable radio sources.
The strangest thing about this signal is its high polarization. It means that its light oscillates only in one direction. However, it rotates with the time," Ziteng Wang, the lead author of the study and a Ph.D student at the School of Physics, University of Sydney.
"The object's brightness also changes dramatically by a factor 100 and the signal switches off and on apparently randomly. It's unlike anything we have ever seen."
Variable light is emitted by many types of stars across the electromagnetic spectrum. Radio astronomy has made tremendous progress, and the study of transient or variable objects in radio waves is an important field of research that helps us uncover the mysteries of the Universe. All types of astronomical objects have brightness that varies, including supernovae, pulsars and flaring stars.
We initially thought it might be a pulsara, a dense type of spinning star or a star that emits large solar flares. However, the signals from this source are not consistent with what we would expect from celestial objects of these types," Mr Wang stated.
Today, the Astrophysical Journal published the discovery of the object.
The object was discovered by Mr Wang and an international team that included scientists from Australia's national scientific agency CSIRO, Germany and the United States. They used the CSIRO ASKAP radio telescope in Western Australia to find it. The South African Radio Astronomy Observatory's MeerKAT telescope was used for follow-up observations.
Artist's impression showing the ASKAP J173608 variable radio signal ASKAP j1736082-321635 arriving at Earth towards the centre the Milky Way. Credit: Sebastian Zentilomo/University of Sydney
Dr. Tara Murphy, also from the Sydney Institute for Astronomy, is Mr Wang's supervisor for his Ph.D.
Professor Murphy stated that: "We have been looking at the sky with ASKAP in order to find unusual objects. This project is called Variables and Slow Transitions (VAST), and will continue through 2020 and 2021.
"We looked towards the center and found ASKAP J173608.2-321635. It was named after its coordinates. The uniqueness of this object was that it appeared to be invisible at first, then became brighter, faded away, and then returned. This was a remarkable behavior.
The astronomers attempted to locate the object in visible light after detecting six radio signals over nine months. They did not find anything.
They then turned to the Parkes radio telescope, but this time they failed to find the source.
Professor Murphy stated that "We then tried out the more sensitive MeerKAT radiotelescope in South Africa. We waited for the signal to return, but it was only intermittent. Every few weeks we kept an eye on it, in hopes of seeing it again.
"Fortunately, the signal returned. However, we discovered that the behavior was drastically different. The source vanished in one day even though it had been there for several weeks in previous ASKAP observations."
This discovery however did not reveal any more information about this transient radio source.
Professor David Kaplan, University of Wisconsin-Milwaukee's cosupervisor for Mr Wang, stated: "The information that we have has some parallels to another emerging class of mysterious objects known at Galactic Center Radio Transients. One of these objects is the 'cosmicburper'.
"While ASKAP J173608.2-321635 shares some properties with GCRTs, there are also differences. We don't know the sources so it adds to the mystery.
Scientists plan to monitor the object closely to find more clues about its nature.
"Within the next ten years, the transcontinental Square Kilometer Array radio telescope (SKA), will be online. Professor Murphy stated that the telescope will be capable of making sensitive maps of every day's sky. We expect that the telescope's power will allow us to solve many mysteries, such as the latest one. However, it will also provide vast new areas of the cosmos for exploration in the radio spectrum.
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Additional information: Astrophysical Journal Discovery of ASKAP J173608.2-321635 As a Highly-Polarized, Transient Point Source with Australian SKA Pathfinder. Information from Astrophysical Journal: Astrophysical Journal Discovery, J173608.2-321635, Highly-Polarized Transient Source with the Australian SKA Pathfinder. (2021). DOI: 10.3847/1538-4357/ac2360
