A sparkling ‘Diamond Ring’ in space: Astronomers in Cologne unravel the mystery of a cosmic ring

An international team led by researchers from the University of Cologne has solved the mystery of an extraordinary phenomenon known as the ‘Diamond Ring’ in the star-forming region Cygnus X, a huge, ring-shaped structure made of gas and dust that resembles a glowing diamond ring. In similar structures, the formations are not flat but spherical in shape. How this special shape came about was previously unknown. The results have been published under the title ‘The Diamond Ring in Cygnus X: an advanced stage of an expanding bubble of ionized carbon’ in the journal Astronomy & Astrophysics.

The ring has a diameter of around 20 light years and shines strongly in infrared light. It is the relic of a former cosmic bubble that was once formed by the radiation and winds of a massive star. In contrast to other similar objects, the ‘Diamond Ring’ does not have a rapidly expanding spherical shell, but only a slowly expanding ring.

“For the first time, we observed the final stage of such a gas bubble in a distinctly flat cloud structure,” explains Simon Dannhauer from the University of Cologne’s Institute for Astrophysics, who lead the study. “The bubble has ‘burst’, because gases were able to escape into the thinner areas around it. All that remained was the particular flat shape.”

Computer simulations show that the bubble initially expanded in all directions and later escaped perpendicular to the cloud. What remained was the structure of the ‘Diamond Ring’ that is visible today. This cosmic formation is estimated to be around 400,000 years old – very young compared to the lifespan of massive stars. Sebastian Vider from the University of Cologne carried out these computer simulations on the new ‘RAMSES’ supercomputer.

The bubble consisting of ionized carbon was once inflated by a hot star with a mass approximately 16 times that of our Sun. This star heats up the gas and dust until it glows. Observations like this are technically very demanding and were only possible with the help of the flying observatory SOFIA (Stratospheric Observatory for Infrared Astronomy). With SOFIA, a modified Boeing aircraft that flies at an altitude of 13 kilometres or more, researchers can observe a wavelength range of light that is not accessible from Earth. In doing so, the researchers were able to precisely measure the movement of the gas: The ring expands at around 1.3 kilometres per second – this corresponds to around 4,700 km/h and is actually quite slow compared to similar bubbles.

The discovery provides valuable insights into how the radiation and winds of young stars shape their environment and therefore also influence the formation of new stars. “The ‘Diamond Ring’ is a prime example of how enormous the influence of individual stars can be on entire cloud complexes,” says Dr Nicola Schneider, co-author of the study. “Such processes are crucial for understanding the formation of stars in our Milky Way,” continues Dr Robert Simon.

Yet there’s still one small disappointment for the romantics. The study also shows that what looks like a ‘Diamond Ring’ from Earth actually consists of two individual objects. It seems as if the ‘Diamond’, a cluster of young stars, is merely part of the ring. In fact, it is located a few hundred light years in front of it.