Astronomers have finally uncovered the origins of one of the most enduring mysteries in radio astronomy – Odd Radio Circles (ORCs). These enigmatic ring-shaped structures in space can be millions of light years across, dwarfing even the largest galaxies.
Starburst Galaxies Linked to ORC Formation
After more than a decade of speculation, observations from the Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope published this week reveal that ORCs form when shells of particles flung out by violent black hole winds in starburst galaxies collide with surrounding intergalactic gas clouds.
“These new observations support our theory that ORCs originate from galactic winds ejected by starburst galaxies about a billion years ago,” said lead researcher Dr. Anna Kapinska from the National Radio Astronomy Observatory.
Starburst galaxies experience extremely high rates of star formation triggered by mergers with other galaxies. The black holes at their centers gorge on infalling gas and matter, causing them to flare up and drive powerful outflows far out into intergalactic space.
“As the black hole winds expand, they eventually strike gas and dust clouds, compressing them into thin shells. It is the collision of these shells over hundreds of millions of years that generates the ORCs,” explained Dr. Kapinska.
Solving a 15-Year-Old Space Mystery
ORCs were first detected in 2009 but their origins have remained mysterious, with theories ranging from shockwaves from ancient supernovae to echoes from black hole formation in the early universe. The new observations provide the first conclusive evidence on their explosive beginnings in starburst galaxies.
“This discovery has been 15 years in the making. The ORCs are like puffy smoke rings floating in space, utterly different from any other objects we have observed,” said Professor Ray Norris from Western Sydney University, who first discovered the ORCs.
Giant Radio Structures Billions of Light Years Across
The mapped ORCs have a typically symmetrical ring shape about 1 million light years in diameter, with some extending over 2 million light years. To put their vast scale into perspective, the ORC shown below is 950,000 light years across – eight times larger than even our galaxy, the Milky Way.
A mapped Odd Radio Circle that is 950,000 light years in diameter, making it many times larger than our own Milky Way galaxy (Credit: Kapinska et al)
What makes the ORCs even more puzzling is that they are formed of synchrotron emission – non-thermal radiation produced by the acceleration of charged particles in magnetic fields. This requires extremely energetic events like supernovae or black hole winds to power them.
“The discovery of hot galactic winds as the source of ORCs was unexpected. But it neatly explains their vast scales, symmetric shapes and strange radio emissions,” said Dr Kapinska.
Studying ORCs to Understand Galaxy Evolution
Unraveling the origins of ORCs sheds new light on the explosive nurturing of galaxies in the early universe. As primitive galaxies grew through mergers and accretion, brief starburst phases likely injected shells and bubbles of gas far out into intergalactic space.
“ORCs provide new insights into how violent outflows from starburst galaxies helped distribute metals and radiation, and even seeded magnetic fields in the early universe,” explained Professor Norris.
There are still unsolved mysteries around ORCs – including why some have a clear ring shape while others appear patchy or broken. Ongoing studies with more sensitive radio surveys could reveal fainter ORC structures that fill our universe.
“This discovery opens up an exciting new window for studying galaxy evolution and testing our theories of how cosmic structures emerged from the Big Bang,” said Dr Kapinska.
The Hunt Continues for More Odd Radio Circles
While the current study has shed light on the beginnings of ORCs, astronomers believe there could be fainter ORCs pervading deep space that are still waiting to be discovered.
Powerful new radio telescopes such as the transcontinental Square Kilometer Array (SKA) coming online in Australia, South Africa and New Zealand will be able to map these structures in unprecedented detail. The SKA’s field of view is expected to be large enough to discover up to 10 million ORCs out to the edge of the observable universe.
“The sensitivity of the SKA will be transformational. We should detect hundreds of thousands of ORCs, allowing us to study the role of galactic winds in evolving galaxies when the Universe was only a quarter of its current age,” said Professor Norris.
The Takeaway
- Astronomers have finally uncovered that Odd Radio Circles originate from galactic winds ejected by starburst galaxies about a billion years ago
- As the black hole powered winds expand outwards, their collision with gas clouds creates ring-shaped synchrotron emission patterns over millions of years that become ORCs
- ORCs can extend over 2 million light years in diameter – vastly bigger than even the Milky Way
- Studying ORCs gives new insight into the explosive growth of early galaxies and distribution of cosmic structures
- More discoveries expected as next-generation telescopes come online to map radio emissions from across the observable universe
The revelation of the explosive origins of ORCs closes a 15 year old mystery about these giant radio structures pervading intergalactic space. But their discovery also opens up new avenues to study galaxy evolution and growth patterns stretching back to the early universe. Astronomers are excited about what new secrets ORCs could unlock with more advanced radio telescopes trained upon the cosmos.
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