Researchers using the Australian Square Kilometre Pathfinder telescope - a wide bandwidth radio telescope based 800 km north of Perth, in the Murchison region of Western Australia - have announced (June 2020) the discovery of what they are calling “Odd Radio Circles”, or ORCs.

We have discovered, to the best of our knowledge, a new class of radio-astronomical object, consisting of a circular disc, which in some cases is limb-brightened, and sometimes contains a galaxy at its centre. None of the known types of radio object seems able to explain it. For example, if the ORCs are SNRs, which they strongly resemble, then this implies a population of SNRs in the Galaxy some 50 times larger than the currently accepted figure, or else a new class of SNR which has not previously been reported.
We therefore consider it likely that the ORCs represent a new type of object found in radio- astronomy images. The edge-brightening in some ORCs suggests that this circular image may represent a spherical object, which in turn suggests a spherical wave from some transient event.Several such classes of transient events, capable of producing a spherical shock wave, have recently been discovered, such as fast radio bursts, gamma-ray bursts, and neutron star mergers. However, because of the large angular size of the ORCs, any such transients would have taken place in the distant past."

See: Unexpected Circular Radio Objects at High Galactic Latitude arXiv, June 2020

It's now assumed that ORCs have a supermassive black hole at their centre. Current theories suggest that :

[…] they could be debris from a huge explosion in their host galaxies, they could come from jets of material spewed out by supermassive black holes or they could come from residual energy from bursts of star formation.

Sounce : New Scentist March, 2022.

Note: Some researchers have suggested that the circles may be the result of 'Gravitational Lensing' (i.e. large-scale distortions of space-time) caused by a black hole nearby the source object ^{[ref. needed]}