Strange radio waves from the heart of the Milky Way


An artistic representation of the strange radio waves emanating from the heart of the Milky Way. These do not look like any radio signals detected before and puzzled scientists as to their origin. The source is named ASKAP J173608.2-321635, after its coordinates in the sky. Image by Sebastian Zentilomo / Sydney University.

Strange radio waves from an unknown source

Radio broadcasting is common in the universe. They are generated by everything from planets and stars – exotic objects like pulsars and black holes – galaxies – and, of course, human technology. This week (October 12, 2021), astronomers noted they detected new and unusual radio wave signals, unlike those found before. The radio waves are coming from the direction of the center of our Milky Way galaxy. And so far scientists haven’t explained them.

Astronomers discovered variable signals using the ASKAP radio telescope in Australia. The behavior of the radio broadcast does not match the pattern of any known source of radio signals. It may be a New sort of stellar object, the scientists said.

Ziteng Wang at the School of Physics at the University of Sydney led the international team of astronomers from Australia, Germany, the United States, Canada, South Africa, Spain and France who observed the signals. They published their Peer reviewed article on the fascinating discovery of The Journal of Astrophysics October 12.

Variable signal with unknown pattern

The source of the signals has been dubbed ASKAP J173608.2-321635, but astronomers do not know what the actual source is. It is located towards the center of our Milky Way galaxy. Wang said:

The brightness of the object […] varies considerably, by a factor of 100, and the signal turns on and off apparently at random. We have never seen anything like it.

Anyway, it is highly polarized and oscillates, as Wang explained:

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 rotates over time.

See an animated representation of the radio signals in the video below:


From the invisible to the visible and vice versa

One of the most amazing things about the source is how it was found. Tara Murphy from the Sydney Institute for Astronomy and the School of Physics said:

We surveyed the skies with ASKAP for new unusual objects with a project known as Slow Variables and Transients (VAST), throughout 2020 and 2021. Looking towards the center of the galaxy, we found ASKAP J173608.2-321635, named after its contact details. This object was unique in that it was first invisible, became shiny, faded, and then reappeared. This behavior was extraordinary.

Astronomers detected six signals over a nine-month period in 2020. But, when astronomers tried to find the source of visual light, using optical telescopes, they saw nothing. The Parkes Radio Telescope in Australia also came empty.

But then the MeerKAT Radio Telescope in South Africa, a network of telescopes more sensitive than Parkes, made detect it. The signal was there, though intermittent and different. Murphy described the signal:

Fortunately, the signal returned, but we found that the behavior of the source was drastically different. The source was gone in a single day, although it had lasted for weeks in our previous ASKAP sightings.

Dark haired man standing in front of an arched doorway in a brick wall.
Ziteng Wang, from the School of Physics at the University of Sydney in Australia, led the research team that discovered the strange radio signals. Image via Sydney University.

What could be the source of the strange radio waves?

Wang and his team have ruled out that this is a pulsar, a rapidly rotating neutron star that emits beams of energy similar to lighthouses:

At first, we 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 don’t match what we’d expect from these types of celestial objects.

The signals also appear to be different from those generated by objects such as supernovae, flaming stars, and rapid radio bursts (FRBs). These items are also variable, but sorry, they don’t match the newly discovered quirk.

However, there seem to be some similarities with other mysterious sources near the galactic center called Galactic center radio transients (GCRT). David Kaplan at the University of Wisconsin-Milwaukee Explain:

The information we have has parallels with another emerging class of mysterious objects known as Galactic Center radio transients, one of which is dubbed the “cosmic burper.”

Although 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.

Bright white spot surrounded by bright cloud-like features, with an arrow pointing to one of them.
GCRT J1745-3009 is a galactic center radio transient (GCRT) in the central region of the Milky Way. GCRTs have some similarities with ASKAP object J173608.2-321635, but there are also differences. Image via NRL / SBC Galactic Center Radio Group / Wikimedia Commons.

Next steps

The discovery is a puzzling mystery for scientists, and naturally they want to figure it out. So what comes next? The researchers plan to continue monitoring the signals as much as they can. In addition, they will receive help with this task, thanks to the construction of a new powerful radio telescope. According to Murphy:

Over the next decade, the transcontinental network of square kilometers (SKA) the radio telescope will be brought online. He will be able to make sensitive charts of the sky every day. We expect the power of this telescope to help us solve mysteries like this latest discovery, but it will also open up vast new areas of the cosmos for exploration in the radio spectrum.

In the meantime, scientists will continue to listen with current telescopes, hoping to find more clues. Whatever this riddle, it will provide exciting new perspectives on our universe.

Conclusion: An international team of astronomers has detected strange radio waves coming from the heart of the Milky Way. They are unlike any other found before and can be from a new type of cosmic object.

Source: Discovery of ASKAP J173608.2–321635 as a highly polarized transient point source with the Australian SKA Pathfinder

Source (pre-publication): Discovery of ASKAP J173608.2-321635 as a highly polarized transient point source with the Australian SKA Pathfinder

Via the University of Sydney

Via the University of Wisconsin-Milwaukee


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