Radio waves

Strange radio waves from the heart of the Milky Way

An artistic representation of the strange radio waves coming from the heart of the Milky Way. These are unlike any radio signals detected before and intrigue scientists as to their origin. The source is named ASKAP J173608.2-321635, based on its coordinates on the sky. Image via Sebastian Zentilomo/ The University of Sydney.

Strange radio waves from an unknown source

Radio emission 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 said they detected new and unusual, unprecedented radio wave signals. Radio waves come from the direction of the center of our galaxy, the Milky Way. And so far, scientists have not explained them.

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

Ziteng Wang at the University of Sydney School of Physics 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 intriguing discovery of The Astrophysical Journal October 12.

Variable signal with unknown pattern

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

The brightness of the object […] varies widely, by a factor of 100, and the signal turns on and off seemingly randomly. We have never seen anything like it.

Anyway, it’s highly polarized and oscillatesas Wang explained:

The strangest property of this new signal is that it has a very high bias. This means that its light oscillates in one direction, but this direction rotates over time.

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

?

From invisible to visible and vice versa

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

We scoured 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 his coordinates. This object was unique in that it started out invisible, became glowing, 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 in 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, did detect it. The signal was there, although intermittent and different. Murphy described the signal:

Fortunately, the signal returned, but we found that the behavior of the source was radically different. The source disappeared in a single day, even though it had lasted for weeks in our previous ASKAP observations.

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. Picture via The University of Sydney.

What could be the source of the strange radio waves?

Wang and his team ruled out that it could be a pulsara rapidly spinning neutron star that emits lighthouse-like beams of energy:

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 do not correspond to what we expect from these types of celestial objects.

The signals also appear to be different from those generated by objects such as supernovae, blazing stars, and fast radio bursts (FRBs). These objects are also variable, but sorry, no match for the newly discovered oddity.

However, there seem to be similarities with other mysterious springs 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 to another emerging class of mysterious objects known as Galactic Center Radio Transients, including one 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 patch surrounded by darker cloud-like features, with an arrow pointing at one.
GCRT J1745-3009 is a Galactic Center Radio Transient (GCRT) in the central region of the Milky Way. GCRTs have some similarities to the ASKAP J173608.2-321635 object, but there are also differences. Image via NRL/SBC Galactic Center Radio Group/ Wikimedia Commons.

Next steps

The discovery is a baffling mystery to 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. Moreover, they will be helped in this task thanks to the construction of a new powerful radio telescope. According to Murphy:

Over the next decade, the transcontinental Square Kilometer Array (S.K.A.) the radio telescope will come online. He will be able to make sensitive maps of the sky on a daily basis. We hope the power of this telescope will help us solve mysteries like this latest discovery, but it will also open up vast new swaths of the cosmos to exploration in the radio spectrum.

In the meantime, scientists will continue to listen with current telescopes, hoping to find more clues. Whatever this puzzle is, it will provide exciting new insights into 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 may 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 (preprint): 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