A variable signal aligned at the heart of the Milky Way intrigues scientists

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Astronomers have discovered unusual signals coming from the direction of the center of the Milky Way. The radio waves do not fit 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 high polarization. This means that its light oscillates in only one direction, but this direction rotates over time,” said Ziteng Wang, lead author of the novella. study and doctoral student. at the University of Sydney School of Physics.

“The brightness of the object also varies considerably, by a factor of 100, and the signal turns on and off seemingly randomly. We’ve never seen anything like it.”

Many types of stars emit variable light across the electromagnetic spectrum. With the tremendous advances in radio astronomy, the study of variable or transient objects in radio waves is a huge field of study that helps us reveal the secrets of the Universe. Pulsars, supernovae, blazing stars, and fast radio bursts are all types of astronomical objects that vary in brightness.

“At first we thought it might 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 don’t match. what we expect from these types of celestial objects,” Wang said.

The discovery of the object was published today in the Astrophysical Journal.

Mr 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 using the ASKAP radio telescope at CSIRO in Western Australia. Follow-up observations were made with the South African Radio Astronomy Observatory’s MeerKAT telescope.

Mr Wang’s thesis supervisor is Professor Tara Murphy, also from the Sydney Institute of Astronomy and the School of Physics.

Professor Murphy said: “We have been scouring the skies with ASKAP for new unusual objects with a project known as Variables and Slow Transients (VAST), throughout 2020 and 2021.

“Looking towards the center 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 and then reappeared. This behavior was extraordinary.”

After detecting six radio signals from the source for nine months in 2020, astronomers attempted to find the object in visual light. They found nothing.

They turned to Parkes’ radio telescope and still failed to detect the source.

Professor Murphy said: “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 we would see it again.

“Fortunately, the signal returned, but we found that the behavior 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.”

However, this new discovery did not reveal much more about the secrets of this transient radio source.

Mr Wang’s co-director, Professor David Kaplan of the University of Wisconsin-Milwaukee, said: “The information we have has parallels with another emerging class of mystery objects known as the Galactic Center. Radio Transients, including one dubbed the “cosmic burper”.

“While our new object, ASKAP J173608.2-321635, shares some properties with GCRTs, there are also differences. And we don’t really understand those sources, anyway, so that adds to the mystery.”

Scientists plan to keep a close eye on the object to look for more clues as to what it could be.

“Within the next decade, the transcontinental Square Kilometer Array (SKA) radio telescope will come online. It will be able to make sensitive maps of the sky every day,” Professor Murphy said. “We hope the power of this telescope will help us solve mysteries like this latest discovery, but it will also open vast new swaths of the cosmos to exploration in the radio spectrum.”

Video showing an artist’s impression of signals from space: https://www.youtube.com/watch?v=J_eGd9Ps9fE&t=5s

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