Odd Radio Circles: Giant explosions in distant galaxies

Uncovering the Mystery of the Odd Radio Circles

Six years ago, astronomers spotted something astonishing: faint, circular radio emissions in the sky—unlike anything seen before. Some doubted they were even real. Today, we know these enormous "Odd Radio Circles" (ORCs), each nearly a million light years wide, surround distant galaxies and may be the aftermath of colossal explosions. But what caused them?

There are now three leading theories to explain what causes ORCs:

• They could be the remnant of a huge explosion at the centre of their host galaxy, like the merger of two supermassive black holes;

• They could be powerful jets of energetic particles spewing out of the galaxy’s centre; or

• They might be the result of a starburst ‘termination shock’ from the production of stars in the galaxy.