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RandomFactor writes:

Four faint objects have been found (archive) by astronomers while mapping the sky in radio frequencies. The objects

are highly circular and brighter along their edges. And they're unlike any class of astronomical object ever seen before.

The objects, which look like distant ring-shaped islands, have been dubbed odd radio circles, or ORCs, for their shape and overall peculiarity. Astronomers don't yet know exactly how far away these ORCs are, but they could be linked to distant galaxies. All objects were found away from the Milky Way's galactic plane and are around 1 arcminute across (for comparison, the moon's diameter is 31 arcminutes).

The ORCs were discovered in the Pilot Survey of the Evolutionary Map of the Universe(EMU), which is using the Australian Square Kilometre Array Pathfinder(ASKAP) radio telescope array in Mid-Western Australia to make a census of radio sources in the sky.

Possible explanations considered in the source paper include

  - Imaging Artifacts
  - Supernova Remnants
  - Galactic Planetary Nebulae
  - Face-on Star-forming galaxy or ring galaxy
  - Lobe from a double-lobed radio galaxy, viewed side-on
  - Lobe from a double-lobed radio galaxy, viewed end-on
  - A bent-tail radio galaxy
  - Einstein Ring
  - Ring around Wolf-Rayet star
  - Cluster Halo
  - Galactic Wind Termination Shock

These are examined in detail and variously discarded.

The submitted paper concludes that the ORCs likely "represent a new type of object found in radio-astronomy images" or "a new category of a known phenomenon" (possibly both.)

A paper describing the objects has been submitted to the preprint site arXiv

Journal Reference:
Norris, Ray P., Intema, Huib T., Kapinska, Anna D., et al. Unexpected Circular Radio Objects at High Galactic Latitude, (DOI: https://arxiv.org/abs/2006.14805)

Original Submission