South African MeerKAT Galaxy Cluster Legacy Survey (MGCLS) Reveals Rare Sighting of ORCs

A team of South African, United States (US) and Australian scientists have discovered an unexplained astronomical object with the help of machine learning. The discovery team 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), spearheaded a team of researchers involved in analysing data from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). This survey, conducted between June 2018 and June 2019, encompassed observations of 115 galaxy clusters using South Africa’s MeerKAT Radio Telescope.

The team achieved a significant breakthrough by identifying the “seventh sighting” of a unique category of radio sources called odd radio circles (ORCs). ORCs derive their name from the striking large rings composed of radio waves. Drawing inspiration from the Lord of the Rings, the Lochner team named their discovery Steep And Uneven Ring Of Nonthermal Radiation (SAURON).

Furthermore, machine learning played a crucial role in detecting SAURON, enabling scientists to uncover this discovery that may have been overlooked. By utilising algorithms capable of autonomously learning patterns and models from available data, scientists used machine learning to bypass the laborious and time-consuming process that could lead to the oversight of novel objects due to human limitations.

In SAURON’s discovery, the team 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 anomalies in large amounts of observation data but curated to the user’s preferences.

“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,” Lochner commented. So instead of combing 6000 individual images generated by the MGCLS, the researchers only had to focus on the first 60 that Astronomaly flagged as abnormal.

Despite the enthusiastic response to the discovery, Michelle Lochner and her team still need to establish conclusive evidence confirming SAURON as an odd radio circle (ORC). Since their initial detection by the Australian Square Kilometre Array Pathfinder (ASKAP) in 2019, only six confirmed sightings of ORCs have been recorded. Scientists are still in the process of comprehending the nature of ORCs and have yet to establish a definitive taxonomic classification for them.

Various theories have emerged to explain the origin of odd radio circles (ORCs). One hypothesis suggests that ORCs may be regular radio galaxies observed from unusual angles. Another proposal suggests that the peculiar ring structures of ORCs could result from intense episodes of star formation. Alternatively, ORCs might be remnants of powerful explosions, possibly triggered by the merger of supermassive black holes. These extraordinarily dense and massive black holes typically reside at the centres of 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. The team aims to prioritise the observation of SAURON by extensively scanning various frequency bands. Through this approach, they anticipate obtaining valuable insights into several aspects, including the magnetic fields surrounding SAURON and the electrons’ varying energies. Detecting the presence of jets would be particularly significant, as it could indicate a collision between supermassive black holes. The team hopes to uncover further details and expand our understanding of SAURON by focusing on these observations.

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 illuminate what is happening in other ORCs.”