Unusual signals from space may hint at a new class of stellar objects



In other exciting news for space enthusiasts, astronomers have discovered unusual signals coming from the direction of the center of the Milky Way. The radio waves do not correspond to any currently understood model of a variable radio source and could suggest a new class of stellar objects. The strangest property of this new signal is that it has a very strong polarization. This means that its light oscillates in only one direction, but that direction spins over time, according to Ziteng Wang, lead author of the new study and a doctoral student at the School of Physics at the University of Sydney. The brightness of the object also varies considerably, by a factor of 100, and the signal turns on and off seemingly randomly. Something like this has never been seen before.
Many types of stars emit variable light across the electromagnetic spectrum, as explained in a statement from the University of Sydney. With the tremendous advancements in radio astronomy, the study of variable or transient objects in radio waves is a vast field of study helping us to reveal the secrets of the Universe. Pulsars, supernovae, flaming stars, and rapid radio bursts are all types of astronomical objects that vary in brightness. Researchers initially thought it could be 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 do not match what one would expect from such celestial objects, as Wang pointed out.
The discovery of the object was published in the Astrophysical Journal. Wang and an international team, including scientists from Australia’s national science agency CSIRO, Germany, the United States, Canada, South Africa, Spain and France discovered the object at the help from CSIRO’s ASKAP radio telescope in Western Australia. Follow-up observations were made with the MeerKAT telescope of the South African Radio Astronomical Observatory. Wang’s thesis supervisor Professor Tara Murphy explained that they had studied the sky with ASKAP to find new unusual objects with a project known as Slow Variables and Transients (VAST), throughout 2020. and 2021. Looking towards the center of the galaxy, they found ASKAP J173608.2-321635, named after its coordinates. This object was unique in that it was initially invisible, glowed, faded and then reappeared. This behavior was extraordinary.
After detecting six radio signals from the source over nine months in 2020, astronomers attempted to find the object in visual light. They found nothing. Subsequently, they turned to Parkes’ radio telescope and again failed to detect the source. Professor Murphy said: “We then tried out the more sensitive MeerKAT radio telescope in South Africa. As the signal was intermittent, we watched it for 15 minutes every few weeks, hoping to see it again. Fortunately, the signal returned, but we found that the source’s behavior was drastically different – the source was gone in a single day, even though it had lasted for weeks in our previous ASKAP observations. However, this new discovery did not reveal much more about the secrets of this transient radio source.
Wang’s co-supervisor, Professor David Kaplan of the University of Wisconsin-Milwaukee, observed that the information they have has parallels with another emerging class of mysterious objects known as Galactic Center radio transients. (GCRT), one of which is dubbed the “cosmic burper”. ‘Although the new object, ASKAP J173608.2-321635, shares some properties with GCRTs, there are also differences. Since scientists don’t really understand these sources, this adds to the mystery. They plan to keep a close eye on the object for more clues as to what it might be.



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