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26 June 2023
Telescope data reveals rare sighting of giant radio wave rings

Machine learning has helped Michelle Lochner to identify an unexplained astronomical object.Credit: Michelle Lochner

An unexplained astronomical object has been observed by a team of South African, US and Australian scientists, with the help of machine learning.

Led by Michelle Lochner, who holds a joint position at the University of the Western Cape (UWC) and the South African Radio Astronomy Observatory (SARAO), the team combed through data generated in the MeerKAT Galaxy Cluster Legacy Survey (MGCLS), a programme of observations of 115 galaxy clusters, run on South Africa’s MeerKAT Radio Telescope between June 2018 and June 2019.

Their prize was the ‘seventh sighting’ of a newly discovered class of radio sources known as odd radio circles (ORCs). ORCs were so named because of their distinctive giant rings made up of radio waves and, in keeping with the Lord of the Rings theme, the Lochner team have chosen to name their finding SAURON, short for a Steep And Uneven Ring Of Nonthermal radiation.

There is a good chance that scientists may have overlooked SAURON were it not for machine learning, which is essentially a set of algorithms that are designed to automatically learn patterns and models from available data. This bypasses the laborious and time-consuming work where because of human constraints, novel objects may go undetected.

In SAURON’s discovery, the team had deployed an ‘anomaly detection framework’ with built-in machine learning capabilities that Lochner developed with collaborators at the University of Cape Town. 'Astronomaly' is designed to pick up on any anomalies in large amounts of observation data, but curated to the user’s specific preferences.

Interesting anomalies

“It uses active learning to combine the raw processing power of machine learning with the intuition and experience of a human user, enabling personalised recommendations of interesting anomalies,” she says.

So instead of having to comb through 6000 individual images generated by the MGCLS, the researchers had only to focus on the first 60 that Astronomaly flagged as anomalous.

But for all the excitement over the discovery, Lochner and her team have yet to confirm that SAURON is indeed an ORC. Since first detected in observations by the Australian Square Kilometre Array Pathfinder (ASKAP) in 2019, only six confirmed sightings have been recorded. Scientists are still figuring out what exactly ORCs are, and ‘are yet to come up with a definitive taxonomic classification.

Some think they are simply normal radio galaxies observed from odd angles. Others propose that ORCs’ strange rings are caused by an intense period of star formation. Or they could be the remnants of a massive explosion, most likely caused by the merger of supermassive black holes, incredibly dense and massive objects that lurk at the centre of most galaxies.“SAURON could plausibly be the result of the enormous release of energy resulting from the rare merger of two of these ‘supermassive’ black holes,” suggests one of the team members, Lawrence Rudnick, Professor Emeritus at the University of Minnesota.

To come up with more concrete answers, Lochner and her collaborators are now pitching for more observation time on MeerKAT, an instrument always in high demand.

“We need more data,” she explains, as SAURON was on the edges of the original field of view provided by MeerKAT. Now the team hopes to put the object front and centre of an observation, while scanning different frequency bands. In this way they hope to glean more insights on, among other things, SAURON’s magnetic fields and the different energies of electrons around it, while also hopefully detecting the presence of jets. The jets, for instance, would serve as evidence of a collision between supermassive black holes.

“If our proposed observations can pin this down,” adds Rudnick, “we can examine the physics of what happens in such extreme, elusive mergers, and the implications for future detections of gravitational waves, galaxy evolution and the production of relativistic particles.”

Securing observation time is far from guaranteed, points out Lochner. But it does help that the project – and the growing interest in ORCs – could answer some big scientific questions, including on the workings of active galactic nuclei.

“SAURON, we believe, is almost like a holotype of such active galactic nuclei, against which others can be compared and measured,” Lochner says. “Its unique physics could certainly shed light on what is happening in other ORCs."

This article was originally published in Nature.