XMM-Newton X-ray data sheds light on mystery of giant 'Cloverleaf'
Astronomers have received new data that helps solve the mystery of the origin of «Cloverleaf» — one of the huge radio rings found around some galaxies. These unusual structures, known as ORCs (odd radio circles), were discovered as recently as 2021 thanks to improvements in the sensitivity of modern radio surveys.
A team of scientists led by Esra Bulbul from the Max Planck Institute for Extraterrestrial Physics in Germany conducted observations of the «Cloverleaf» in the X-ray range using the European space telescope XMM-Newton. This was a key point in unraveling the mystery of the formation of this giant structure.
«This is the first time anyone has seen X-rays associated with ORC», — noted Bulbul.
The findings showed that the X-ray emission comes from hot gas with a temperature of about 9 million degrees Celsius, distributed within a group of galaxies contained in the Clover Leaf. Analysis of this radiation led to the conclusion that two separate groups of galaxies collided here, which in the process of merger created this giant radio ring. This, in turn allowed us to estimate the total mass of the system— about a dozen galaxies. The gravitational pull of the united system caused the surrounding gas to fall inward and become extremely heated.
«The energy required to create such extensive radio emission is very high. Some simulations can reproduce their shape, but not their intensity. No simulations explain how ORC was formed, — Bulbul explained.
«Galaxies constantly interact and merge. But the source of accelerated particles that create powerful ORC radio emission is still unclear to us», — notes NASA's Kim Weaver.
One hypothesis links the radio emission to relic electrons from past supermassive black hole activity that were re-accelerated during the merger of groups of galaxies.
«Mergers form the basis of structure formation, but there is something special in this system that leads to a sharp increase in radio emission», — says Esra Bulbul.
Although scientists have been able to significantly clarify the nature of the “Clover” leaf, many questions remain unanswered. Currently, more detailed observations of this unusual object are planned using radio and X-ray telescopes.
«We can figure out a lot from careful observations because such interactions require all kinds of physics. This object contains almost everything we deal with in space. It's like a mini-universe, — notes Weaver.