Astronomers are usually familiar with stars, planets, black holes, and galaxies. But in 2019, something new caught their attention. The ASKAP telescope in Australia detected mysterious circles in space, each large enough to encircle whole galaxies. These were something entirely new and unobserved before.
A composite View of an ‘Odd radio circle’ known as ORC J2103-6200. - Made from MeerKAT Telescope's 2022 Radio Image Combined with Dark Energy Survey's Optical Data (
Credit: Jayanne English using data from MeerKAT and the Dark Energy Survey via Wikimedia Commons)
Now Professor Alison Coil from the University of California San Diego and her team think they've figured out what these circles are. They believe they are giant shells created by winds blowing out from galaxies. These winds might come from supernovae, which are massive stars that explode at the end of their life.
When many stars in a galaxy explode near each other, they can push gas out of the galaxy at incredible speeds, up to 2,000 kilometers per second. This process is especially common in "starburst" galaxies, where stars form very quickly. When two big galaxies collide, they can create a starburst galaxy, leading to these massive outflows of gas.
ASKAP's advanced technology allowed it to find these odd radio circles (ORCs) for the first time. They're huge - hundreds of times larger than our Milky Way galaxy. Various theories were proposed to explain them, but Coil's team used a mix of radio, optical, and infrared data to study them in detail. They focused on one of these ORCs, named ORC 4.
An artistic interpretation of strange radio circles bursting forth from a central galaxy. ORC’s can eventually expand past other galaxies.
(Credit: Illustration: Sam Moorefield; Data: CSIRO, HST (HUDF), ESA, NASA; Image: J. English (U. Manitoba), EMU, MeerKAT, DES, CTIO via Wikimedia Commons)
Their research showed that ORC 4's galaxy had a burst of star formation that ended about a billion years ago. They used computer simulations to understand how these ORCs formed. The simulations suggested that these winds blew for 200 million years before stopping. When they stopped, they created a shockwave that pushed hot gas out of the galaxy, forming a radio ring.
Coil believes that these ORCs can teach us a lot about galactic winds and the evolution of galaxies. They might help us understand if all big galaxies go through an ORC phase and how galaxies change over time. This discovery opens up new ways to study and understand our universe.
The team published their findings in the peer-reviewed science journal Nature, listed below this article for those interested.
Sources and further reading:
MeerKAT uncovers the physics of an odd radio circle (Monthly Notices of the Royal Astronomical Society)
Ionized Gas Extended Over 40 kpc in an Odd Radio Circle Host Galaxy (Nature)
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