Astronomical mystery becomes clearer thanks to SKA precursors

BY RACHEL RAYNER (CSIRO)

Astronomy’s newest strange objects, odd radio circles, have been pulled into sharp focus by astronomers using two of the world’s most capable radio telescopes.

When first revealed in early 2021 by the ASKAP telescope, owned and operated by CSIRO in Western Australia, odd radio circles quickly became an object of fascination. Theories around their origins ranged from galactic shockwaves to the throats of wormholes.

Now, a new detailed image captured by SARAO’s MeerKAT radio telescope and published in Monthly Notices of the Royal Astronomical Society, is providing researchers with more information on the circles’ composition and shape.

“People often want to explain their observations and show that it aligns with our best knowledge. But to me, it’s much more exciting to discover something new, that defies our current understanding,” says researcher Dr Jordan Collier of the Inter-University Institute for Data Intensive Astronomy in South Africa, who compiled the image from MeerKAT data.

Colour was assigned to data from ASKAP (turquoise) and MeerKAT (mint) radio telescopes, as well as to optical and near infra-red data from the Dark Energy Survey. The colour images were subsequently combined to create this composite image of an odd radio circle (ORC).

Credit: J. English (U.Manitoba)/EMU/ASKAP/MeerKAT/DES(CTIO)

Only five odd radio circles have ever been revealed, and all in 2021. So far, it is known that they are rings of faint radio emissions surrounding a galaxy with a highly active black hole at its centre. How they came to exist, and why they are so rare, we still don’t know.

“We always expected that next-generation telescopes like ASKAP and MeerKAT would probably stumble across unexpected new discoveries, but we didn’t think it would happen so quickly,” says leading researcher, Prof. Ray Norris from Western Sydney University and CSIRO.

ASKAP is the only telescope so far that can find odd radio circles. Despite being 16 times bigger than our own galaxy, odd radio circles are hard to see. However, ASKAP’s swift, comprehensive and sensitive scans of the sky enable it to discover new, faint objects. MeerKAT in South Africa can then home in on these objects and give us a clearer, more in-depth image, as it did with odd radio circles. The MeerKAT image identified more than one ring encircling a radio-active elliptical galaxy. This narrows down potential theories but it will take more teamwork and technology to get to the truth.

“With their incredible capabilities, ASKAP and MeerKAT are set to revolutionise our understanding of the Universe faster than ever before,” said Professor Norris.

Read the paper: https://arxiv.org/abs/2203.10669

CSIRO acknowledges the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site where ASKAP is located.

The discovery image of ORC-1 in the EMU survey’s ASKAP data is seen on the left, while the follow-up observation using MeerKAT is on the right. Both images display radiation from a large range of sequential radio frequencies. Using both the ASKAP and MeerKAT telescopes provides a broad range of spatial scales that include diffuse emission and detailed structure.

EMU/ASKAP/MeerKAT