by Scientists may have finally solved the mystery of cosmic ORCs, or “odd radio rings” as they are officially called, which are so large that they are 10 times the width of the Milky Way and can contain entire galaxies.
A team of astronomers led by University of California San Diego Professor of Astronomy and Astrophysics Alison Coil has pointed to powerful winds erupting from exploding galaxies, or supernovae, as the cause of giant shells of gas seen in radio waves as ORCs. The research was revealed Wednesday (January 8) at the 243rd meeting of the American Astronomical Society in New Orleans.
ORCs were first spotted by the Australian Square Kilometer Array Pathfinder (ASKAP) in 2019 and were the most mysterious thing astronomers had ever seen.
Coil and her team used the central field spectrograph at the WM Keck Observatory on the inactive Maunakea volcano on the island of Hawaii to observe the ORC 4 radio ring, finding inside highly compressed gas and stars with an age of roughly 6 billion years. This led the team to understand that these radio rings could be created when multiple stars explode near each other in the same galaxy.
Related: Cosmic Orcs? Scientists snap best image yet of ‘odd radio circles’ in space
Do cosmic ORCs tell the story of the stars from cradle to grave?
When massive stars reach the end of their lives and explode in a supernova explosion, vast amounts of interstellar material are expelled as a powerful wind into the surrounding galaxy.
Coil and colleagues think that if many supernovae occur in the same area of space at about the same time, these winds can be driven to speeds as high as 4.5 million miles per hour, about 5,000 times as fast as a bullet fired from a handgun. .
The question is, what kind of galaxies would harbor so many stars exploding around the same time?
This can happen in galaxies that have experienced bouts of intense star formation, which astronomers call “starburst” galaxies.
“These galaxies are fascinating,” Coil said in a statement. “They happen when two large galaxies collide. The merger squeezes all the gas into a very small region, resulting in an intense burst of star formation.”
The massive stars formed in the composite form of a fast star that triggered a merger, burn through their fuel for nuclear fusion at the same rapid rates, erupting in supernova explosions and expelling gas as outflow winds at similar times.
As these winds rip out of these galaxies, they hit slower moving gas around the galaxy. This interaction creates a shock wave that generates ORCs, which can extend for hundreds of thousands of light years. To put that in context, the Milky Way is about 98,000 light years wide and one light year is the distance light travels in a year, about 6 trillion miles (9.7 trillion kilometers).
Solving the mystery of the Cosmic ORCs
Prior to the development of this star-driven supernova-wind theory of a constellation, scientists had proposed several other creation mechanisms to explain ORCs. These included the merger of two black holes and the formation of planetary nebulae during the supernova explosions that end the life of a star.
The problem was that ORCs were only visible in radio waves, and this data was not enough to distinguish between possible creation models.
Suspecting that ORCs might be the result of later stages of the starburst galaxies they were investigating, Coil and her team began studying ORC 4, the first known example of these radio shells visible from the Northern Hemisphere, with the central field. spectrograph at the WM Keck Observatory. This revealed to them a vast volume of bright, highly compressed gas.
Continuing their detector work and using radio wave data and optical light observations, the team found that the stars within ORC 4 were about 6 billion years old, suggesting that there had been a burst of formation intense star has happened in the heart of this radio circle that ended. about 1 billion years ago.
The team then turned to a computer simulation developed by research co-author and Harvard & Smithsonian Astrophysics galactic wind specialist Cassandra Lochhaas to further their investigation.
The simulation allowed the team to watch the development of ORC 4 over a period of 750 million years, slightly less than the estimated 1 billion years of its existence.
Replicating the size and properties of ORC 4 and accounting for the massive amount of turbulent gas in the galaxy at its core, the simulation showed galactic winds flowing out over a period of about 200 million years.
Even when these winds stopped, the shock wave they sent continued to push its way forward, blasting hot gas out of the galaxy, creating the radio ring that encloses it, and forcing cooled gas back in. in the galaxy.
“To make this work you need a high-mass outflow rate, which means it’s shedding a lot of material very quickly. And the surrounding gas just outside the galaxy has to be low-density; otherwise, the shock stalls. These are the two key. factors,” Coil said. “The galaxies we are studying clearly have these high outflow rates.
“They’re rare, but they do exist. I really think this indicates ORCs arising from some sort of outflow galactic winds.”
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Because of the revelation that ORCs like ORC 4 are most likely the result of outflowing galactic winds, these radio circles can be used as a proxy to study these powerful winds and answer important questions about evolution galactic.
“ORCs provide a way for us to ‘see’ the winds through radio data and spectroscopy. This can help us determine how common these large outflow galactic winds are and what the lifetime of the wind is,” said Coil. “They can also help us learn more about galactic evolution: do all massive galaxies go through an ORC phase? Do spiral galaxies turn elliptical when they are no longer stars?
“I think there is a lot we can learn about ORCs and learn from ORCs.”
In addition to appearing at the American Astronomical Society meeting in New Orleans, the team’s research is also detailed in the Jan. 8 issue of the journal Nature.
