Astronomers have uncovered a vast cloud of energetic particles surrounding one of the most distant galaxy clusters ever observed, shedding new light on the evolution of galaxy clusters in the early universe.
Co-led by Université de Montréal's Julie Hlavacek-Larrondo, the scientists say their finding shows that entire galaxy clusters, among the largest structures in the Universe, have been immersed in high-energy particles for most of their existence.
The discovery, at a distance so great that it takes light 10 billion years to reach Earth, is the most distant 'radio mini-halo' ever found, doubling the previous record.
Such a mini-halo consists of highly energetic charged particles in the vacuum between galaxies in a cluster, which together emanate radio waves that can be detected from Earth.
Accepted for publication in Astrophysical Journal Letters, with the pre-print version of the paper published today, the discovery shows that even in the early universe, galaxy clusters were already shaped by energetic processes.
And understanding how energy moves through galaxy clusters will help in piecing together the story of cosmic evolution, the astronomers say.
Two likely explanations
There are two likely explanations behind the formation of the mini-halo.
One is that there are supermassive black holes which lie at the hearts of galaxies within a cluster and can eject streams of high-energy particles into space.
However, astronomers are still trying to understand how these particles would be able to migrate away from the black hole to create such a gigantic cloud of particles, while maintaining so much of their energy.
The second explanation is cosmic particle collisions.
This is when charged particles within the hot plasma of the galaxy cluster collide at near-light speeds, smashing apart into the highly energetic particles that make up the mini-halo.
The astronomers say their finding offers a rare look at what galaxy clusters were like just after they formed. It not only shows that galaxy clusters have been infused with high-energy particles for billions of years more than previously known but also allows scientists to study where these high-energy particles come from.
"It's astonishing to find such a strong radio signal at this distance," said Roland Timmerman, a Durham University (U.K.) astronomer who co-led the discovery with Hlavacek-Larrondo. "It means these energetic particles and the processes creating them have been shaping galaxy clusters for nearly the entire history of the universe."
About this study
''Discovery of Diffuse Radio Emission in a Massive z=1.709 Cool Core Cluster: A Candidate Radio Mini-Halo'', by Julie Hlavacek-Larrondo and her colleagues is published in the Astrophysical Journal Letters.
