Astronomers have an explosive theory of the origin of mysterious radio circles in space

Strange radio circles, also known as ORCs, are so massive that entire galaxies are located at their centers, and the objects themselves extend for hundreds of thousands of light years, CNN reports.

Our Milky Way galaxy is 30 kiloparsecs across, and one kiloparsec is equal to 3260 light years. Odd radio circles measure hundreds of kiloparsecs across. So far, only 11 have been discovered, and some of them are potential ORCs that the researchers say have not been confirmed.

As CNN continues, astronomers have put forward many theories to determine what could form the cosmic rings, including that they are the result of massive cosmic collisions. But new research suggests the circles are shells formed by powerful galactic winds created when massive stars explode.

Astronomers first spotted the strange radio circles using the SKA Pathfinder telescope, operated by Australia’s national science agency CSIRO, or the Commonwealth Scientific and Industrial Research Organization.

The telescope can scan large areas of the sky for faint signals, allowing scientists to detect unusual objects.

Researchers using the South African Radio Astronomy Observatory’s MeerKAT telescope also took the first image of ORC, designated ORC 1, in 2022. The powerful telescope is sensitive to weak radio emissions.

The theories emerged after strange radio circles were discovered: they could be the mouths of wormholes, remnants of black hole collisions, or powerful jets emitting energetic particles, researchers suggested.

But until the new study, the circles were observed only using radio waves. Despite their enormous size, neither visible light, nor infrared, nor X-ray telescopes have detected the strange radio circles.

UC San Diego astronomy and astrophysics professor Alison Coyle and her collaborators decided to take a closer look at ORC 4, the first known strange radio circle observed from Earth’s Northern Hemisphere. Coyle and her team studied ORC 4 using the W.M. Observatory. Keck in Hawaii, which revealed the presence of more glowing, heated gas in visible light than is observed in typical galaxies.

The discovery only raised more questions.

Coyle, tells CNN, was fascinated by the unusual radio circles because she and her fellow researchers study massive “starburst galaxies,” which have high star formation rates. Galaxies can also produce rapidly spreading winds. When giant stars explode, they release gas into interstellar space, or the space that exists between stars.

When enough stars explode simultaneously, the force of the explosion can expel gas from the galaxy in which the stars are exploding at speeds of up to 4,473,873 miles per hour (2,000 kilometers per second).

“These galaxies are really interesting,” says Coyle, lead author of the study and chair of the Department of Astronomy and Astrophysics at the University of California, San Diego. “They occur when two large galaxies collide. The merger pushes all the gas into a very small area, causing an intense burst of star formation. Massive stars burn out quickly, and when they die, they release their gas in the form of outgoing winds.”

Coyle and her team thought that the radio rings might be associated with galaxies where stars are exploding.

Using visible and infrared data, the Coil team estimated that the stars in the galaxy inside ORC 4 are 6 billion years old.

“There was a burst of star formation in this galaxy, but it ended about a billion years ago,” says Coyle.

Then study co-author Cassandra Lochhaas, a graduate student at the Harvard-Smithsonian Center for Astrophysics, ran simulations to recreate the size and properties of the radio circle, including the amount of gas they detected with the telescope.

The Lochhaas simulation showed that the outgoing galactic winds blew for 200 million years before stopping. The forward-moving shock wave then continued to eject hot gas from the galaxy, creating a radio circle. Meanwhile, the blowback sent cooler gas back into the galaxy. These events took place over a period of approximately 750 million years.

The new research was published in the journal Nature and presented at a meeting of the American Astronomical Society in New Orleans.

“For this to work, you need a high mass efflux rate, which means it ejects a lot of material very quickly. And the surrounding gas immediately outside the galaxy must be low density, otherwise the shock wave will stop. Those are two key factors,” says Coyle. “It turns out that the galaxies we studied have such high mass outflow rates. They are rare, but they exist. I do think this indicates that the ORCs come from some kind of outgoing galactic winds.”

Understanding the origins of strange radio circles also helps astronomers ultimately understand the impact these phenomena may have on the formation of galaxies over time.

“ORCs give us the ability to ‘see’ the winds using radio data and spectroscopy,” Coyle notes. “This could help us determine how common these extreme galactic winds are and what the life cycle of the wind is. They can also help us learn more about galaxy evolution: do all massive galaxies go through an ORC phase? Do spiral galaxies become elliptical when they no longer form stars? I think we can learn a lot about ORC and learn from them.”