Astronomers have finally uncovered the mysterious origins of strange ring-shaped radio signals detected from distant galaxies, known as “odd radio circles” (ORCs). These enormous and perplexing radio structures, spanning up to 5 million light years across, have puzzled scientists since their initial discovery in 2019. Now, new observational data reveals that ORCs likely originate from powerful winds erupting from intense bursts of star formation within galaxies.
Starburst Galaxies Spew Enormous Galactic Winds
Researchers using the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope first detected ORCs in 2019. The bizarre structures remained an enigma until data from the Karl G. Jansky Very Large Array (VLA) in New Mexico recently provided key insights, published this week in the journal Nature.
By examining radio signals from ORCs in greater detail, a team led by Anna Kapinska at the National Radio Astronomy Observatory pieced together their likely origins. The data suggests ORCs form within rare “starburst” galaxies experiencing extremely high rates of star birth. As massive young stars rapidly ignite, their stellar winds and violent supernova explosions drive huge outflows of gas into space – galactic winds extending far beyond the galaxies themselves.
“The explosive and short-lived nature of starburst events means we have been lucky to capture them” said Dr. Kapinska in a statement. “The supernovae and winds from the stars collide with and shock the surrounding material, producing these strange radio circles.”
Radio Structures Billions of Lightyears Across
Unlike spiral galaxies such as our own Milky Way, ORCs emerge from turbulent galaxies undergoing intensely concentrated bursts of star formation. As these stellar explosions rend gases outward in spherical bubbles up to 1.6 million light years wide, they continue traveling hundreds of thousands to millions more lightyears into intergalactic space.
Stacked radio imagery from the VLA revealed the hollow, spherical structures created by this process. Some ORCs span 3 million to 5 million light years in diameter – enormous even compared to their already massive host galaxies.
“The large size of ORCs means the winds must be extremely powerful in order to spread so far from their host galaxies” said Dr. Kapinska. “No other galaxy population, not even the most extreme starbursts, have properties that can explain these enormous radio bubbles.”
What Causes Odd Radio Circle Formation?
While the new observations have settled the long-standing mystery, more questions remain. In particular, researchers want to know why ORCs shine so brightly at radio frequencies.
One possibility involves cosmic rays – high energy subatomic particles which pervade intergalactic space. As galactic winds collide, they may accelerate cosmic rays even more. Interactions between these energetic particles and magnetic fields within the bubbles then produce the observed radio glow.
Alternatively, amplified magnetic fields themselves, amplified and stretched by powerful shockwaves, may directly emit the radio waves as they realign. Further observations to differentiate these mechanisms are underway.
Either way, ORCs clearly trace immensely strong bursts of stellar winds. Capturing galaxies during these brief epochs offers valuable insights into the stellar lifecycle. “ORCs are the smoking gun evidence of the most extreme starbursts that can exist” said Dr Ray Norris of Western Sydney University. “It’s amazing that ASKAP was able to find them.”
With the basic riddle of ORCs solved, astronomers now want to spot and scrutinize more of them. The initial sample included just 9 circles, but models suggest thousands may populate skies across the universe. New radio surveys by ASKAP, MeerKAT in South Africa, and eventually the Square Kilometre Array (SKA) should uncover far more specimens.
“One of the wonderful aspects of astronomy is how solving one mystery reveals several more” said Dr. Kapinska. Detailed multiwavelength follow-up will dig deeper into cosmic ray acceleration and magnetic amplification inside ORCs. Analyzing their properties will deliver insights into the intense star formation environments giving rise to them. And statistical samples can constrain just how frequently galaxies undergo such explosive phases, with consequences for stellar and galactic evolution models.
“While questions remain, pinpointing the source of ORCs after years of uncertainty is an important leap forward” concluded Dr. Kapinska. “This breakthrough illustrates how next-generation radio observatories like the SKA will catalyze discoveries about the hidden, dynamic Universe.”
|3 – 5 million lightyears
|Host galaxy type
|Radio frequency signature
|Bright; probable synchrotron radiation
|Powerful winds from concentrated bursts of star formation
So in summary, astronomers have revealed that these enigmatic giant radio structures likely originate from short-lived explosive outflows driven by intense starburst episodes in galaxies billions of lightyears distant. Though puzzles persist, pinpointing an origin for these record-breaking radio bubbles represents a major advance. And their sheer size and intensity offers valuable insights into the extremes of stellar lifecycles and evolution. Uncovering more odd radio circles with next-generation telescopes promises further discoveries about the dynamic and often hidden processes continuously shaping our Universe.
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