SAN DIEGO (AP) — Astronomers at the University of California, San Diego may have unraveled the mystery behind giant circles of radio waves that were first observed in 2019 in the depths of space. The team discovered that these odd radio circles (ORCs) are formed by outflowing winds generated by explosive events like supernovas. This finding sheds light on the formation and nature of these enigmatic structures.
According to the astronomers, when multiple massive stars die and explode in close proximity, the resulting force pushes the surrounding gas outward, creating outflowing winds traveling at speeds of over 1,200 miles per second. It is this sheer force from the outflowing winds that shapes the shells composing the ORCs, which can be more than 50,000 times the diameter of our Milky Way galaxy.
To investigate further, the team conducted simulations that replicated outflowing galactic winds over a span of 200 million years. They observed that when the winds come to a halt, a forward-moving shock expels high-temperature gas out of the galaxy, forming a radio ring. Subsequently, a reverse shock propels cooler gas back into the galaxy, completing the cycle.
The discovery of these radio wave circles was made possible through the Australian Square Kilometer Array Pathfinder (ASKAP) in 2019. Prior to that, astronomers could only detect ORCs through radio emissions, lacking visual data. This breakthrough prompted the researchers to explore how and why ORCs were formed.
Previous theories about the origins of ORCs included planetary nebulae and black hole mergers, but these were ultimately discarded. Instead, the new findings implicate starburst galaxies as the creators of ORCs. Using optical and infrared imaging, the team determined that the stars within the ORC 4 galaxy were approximately six billion years old.
According to Alison Coil, an astrophysicist involved in the study, the ORCs originate from outflowing galactic winds. She noted that these galaxies have high-mass outflow rates, indicating that ORCs are relatively rare but do exist. The ASKAP, known as the world’s fastest telescope, played a pivotal role in detecting and studying ORCs, allowing astronomers to examine these structures that stretch across vast expanses in the sky.
The new insights gained from this research will contribute to a deeper understanding of how galaxies form and evolve, as well as the role and prevalence of outflowing galactic winds. In the future, astronomers hope to uncover whether all massive galaxies go through an ORC phase and if spiral galaxies transition to elliptical galaxies when star formation ceases. This ongoing investigation holds great potential for further discoveries in the exciting field of astrophysics.