Fans of the late 1970s sitcom “Mork & Mindy” know Robin Williams’ extraterrestrial character Mork came from the mysterious planet Ork. Over 40 years later, some new and equally mysterious ORCs have appeared – ‘odd radio circles’ in weird roundish shapes measuring a few million light-years in diameter. While previously only detected in radio wavelengths, astronomers recently managed to capture a close-up image of an ORC and it’s beautiful in a weird way … and vice versa. Do these ORCs ban humor like Mork’s Ork did?
“Odd Radio Circles (ORCs) are recently-discovered faint diffuse circles of radio emission, of unknown cause, surrounding galaxies at moderate redshift (z ∼ 0.2 − 0.6).”
In research published this week in the journal Monthly Notices of the Royal Astronomical Society, a team of astronomers explain how they discovered the first ‘odd radio circle’ in 2019 using the Australian Square Kilometre Array Pathfinder radio telescope. Since then, five ORCs have been confirmed but their origins are a mystery -- theories range from galactic shockwaves to wormholes. To get a clear image of one, the same astronomers used South Africa’s MeerKAT telescope and captured a beautiful image (which can be seen in the journal here). They also created an animation showing how the ORC may have looked as it exploded out of a galaxy (view it here). The question is – what caused such an explosion?
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;
- They might be the result of a starburst ‘termination shock’ from the production of stars in the galaxy
In the CISRO press release (CISRO is Australia’s national science agency which owns and operates the ASKAP telescope), theorizes on the origins of these enormous ORCs – the rings are about a million light years across or 16 times bigger than the Milky Way. Inside them is a galaxy with a highly active black hole, and the ORC envelopes other galaxies as it expands. Despite their size, these radio emission rings are faint and extremely rare, so astronomers are looking for bigger telescopes with more power than MeerKAT and ASKAP. One obvious possibility is the Square Kilometre Array (SKA), an intergovernmental radio telescope project being planned for Australia and South Africa with a completion date in the late 2020s.
Check out the paper – the photos and illustrations are extraordinary. Has there ever been a better time to be an astronomer?
Mork from Ork would certainly agree.