Mysterious Large-Scale Radio Circles in Space: An Explained Phenomenon
In 2019, astronomers discovered mysterious radio circles in space, vast in their scale with diameters spanning hundreds of thousands of light-years. For scale, consider our Milky Way galaxy, which is 100,000 light-years in diameter. But what causes these circles? It appears that the enigma has finally been solved.
The Odd Radio Circles (ORCs)
These radio circles are labeled ‘odd radio circles’, or ORCs. They are significantly large, circular, and visible at the frequency of radio radiation but remain invisible in the spectrum of visible, infrared, or X-ray radiation. To date, astronomers have identified five such objects.
The Origin of ORCs
A team of scientists reported in a paper in Nature that these circles are created by supernova explosions. Stars at the end of their life cycle, when they explode, eject scorching hot gases. Suppose multiple stars explode within a brief period, a likely occurrence in active star-forming regions, this would propel the gases fast enough to escape the confines of the galaxy. The gases may achieve a speed of 2000 kilometers per second, slightly less than 1% of the speed of light, which is 300,000 kilometers per second.
Star Collision & Galactic Winds
“These galaxies are quite fascinating,” reveals Alison Coil, the lead researcher. “When two galaxies collide, the gas is compressed. Consequently, a large number of stars can form in a short time. These massive stars also perish quickly, giving rise to swift galactic winds.”
Coil and her colleagues unravelled the mystery by examining ORC 4, one of the discovered radio circles. They found that the stars in ORC 4 were approximately six billion years old, and there had been a period of active star formation a billion years ago. Researcher Cassandra Lochhaas undertook several computer simulations to replicate the radio circle and found that the galactic winds were active for about 200 million years before they ceased.
The Rarity of Met Conditions for ORCs
While not many ORCs have been found yet, this is attributed to the need for perfect conditions for their occurrence. A large amount of material must be ejected in a short time, and the gas outside the galaxy must have a low density; otherwise, the shockwave halts. “These galaxies are rare, but they exist,” concludes Coil.
A Challenge to Astronomers & Noteworthy Question to Answer
Now that astronomers understand the cause of the ORCs, it is time to answer a crucial follow-up question: Have all large galaxies undergone a phase where they had a radio circle? Addressing this would enhance scientists’ understanding of the evolution of galaxies.
