XMM-Newton X-ray satellite captures “space clover” from a new perspective

Astronomers have discovered giant circular radio structures of unknown origin around several galaxies. Now, new observations of the so-called cloverleaf suggest it was formed by the collision of a group of galaxies. Studying these structures, collectively known as ORCs (Odd Radio Circles), from a different perspective has provided scientists with the opportunity to study everything from supersonic shock waves to the behavior of black holes. “This is the first time that we have observed X-ray emissions associated with ORCs,” said Esra Bulbul, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who led the study. “The key to unlocking the secret of shamrock’s birth was missing.” A paper describing the results was published April 30 in Astronomy and Astrophysics Letters. accidental discovery Until 2021, no one knew about ORC. Thanks to improvements in technology, radio surveys have become more sensitive enough to pick up such weak signals. Over the course of several years, astronomers discovered eight of these strange structures randomly scattered around the outer reaches of the galaxy. Each is large enough to contain an entire galaxy, and in some cases multiple galaxies. “The power required to generate such widespread radio radiation is extremely powerful,” Bulbul said. “Some simulations can reproduce the shape, but not the strength. There are no simulations that explain how to create an ORC.” When Bulbul learned that the ORC was not being studied with her We began combing through data from the Extended Roentgen Survey with Imaging Telescope Arrays. Based on an observation time of less than 7 minutes, they noticed X-ray emissions that appeared to be coming from the trefoil. This gave them the power to assemble a larger team and secure additional telescope time on her ESA (European Space Agency) mission, XMM-Newton, with contributions from NASA.

The time allotted to us was about five and a half hours and the data arrived late in the evening in November,” Bulbul said. “I forwarded it to Xiaoyuan, and he came to my office the next morning and said, I found it!'' I couldn't help but cheer!'' "We were really lucky," Zhang said. "The eROSITA observations showed some plausible X-ray point sources near the ORC, but not the widespread emission seen with XMM-Newton. It turns out it couldn't have come from a clover leaf.'' That's enough to convince us to take a closer look. ” galactic galactic The X-ray emissions track the distribution of gas within the galaxy cluster, like police tape around a crime scene. By observing how this gas is disturbed, scientists discovered that the galaxies embedded in the cloverleaf were actually two separate groups that were close enough to merge. determined to be a member of. The temperature of the emission also provides clues about the number of galaxies involved. When galaxies merge, their combined mass increases and their gravitational pull increases. The surrounding gas begins to fall inward, heating the incoming gas. The greater the mass of the system, the higher the temperature of the gas. Based on the X-ray spectrum of the emission, its temperature is approximately 15 million degrees Fahrenheit, or between 8 and 9 million degrees Celsius. "From these measurements, we can infer that the Cloverleaf ORC is hosted by about 12 galaxies that are attracted to each other, which is consistent with what we see in deep visible light images," Zhang said. Ta. The researchers believe that nuclear fusion may have created shock waves, accelerated particles, and emitted radio waves. "Galaxies are constantly interacting and merging," said Kim Weaver, NASA XMM-Newton project scientist at NASA Goddard Space Flight Center in Greenbelt, Maryland. He was not involved in this study. "However, the source of the accelerated particles is unknown. One interesting idea about the strong radio signal is that resident supermassive black holes have experienced extreme activity in the past, and this ancient activity This means that the remaining electrons from theevent” were accelerated again by this merger. ” Galactic group mergers are common, but ORCs are extremely rare. And it’s still unclear how these interactions cause such powerful radio emissions. “Fusion is the backbone of structure formation, but there’s something special about this system that increases radio emissions,” Bulbul says. “At the moment we can’t say what it is, so we need more and more detailed data from both radio telescopes and he X-ray telescopes.” Although the research team solved the mystery surrounding the nature of Cloverleaf’s ORC, it also raised other questions. They plan to study Shamrock more closely to find answers. “There’s all kinds of science involved in these interactions, so we can learn a lot from more thorough observations,” Weaver says. “Pretty much everything we’re dealing with in space is packed into this little package. It’s like a mini-universe.”

source: http://dx.doi.org/10.1051/0004-6361/202449900