This mini halo is the most distant ever observed, surpassing the previous record by a factor of two. Its discovery confirms that galaxy clusters have been enveloped in high-energy particles for most of their lifetimes, extending back to the early universe.
Mini halos are regions between galaxies in a cluster filled with charged, high-energy particles that emit faint radio waves detectable from Earth. The discovery, accepted for publication in The Astrophysical Journal Letters, reveals that such energetic structures were already forming in the infant universe.
Led by Julie Hlavacek-Larrondo of Universite de Montreal and Roland Timmerman of Durham University, the international team analyzed radio data from the Low Frequency Array (LOFAR), a European telescope network. While studying the SpARCS1049 galaxy cluster, they detected a diffuse radio glow not linked to individual galaxies but to a region over a million light-years across.
"It's as if we've discovered a vast cosmic ocean, where entire galaxy clusters are constantly immersed in high-energy particles," said Hlavacek-Larrondo.
Timmerman added, "It's astonishing to find such a strong radio signal at this distance. It means these energetic particles and the processes creating them have been shaping galaxy clusters for nearly the entire history of the universe."
Scientists propose two main mechanisms for the mini halo's origin. One involves supermassive black holes at the centers of galaxies expelling high-energy particle jets. Another involves collisions among charged particles within the hot plasma of galaxy clusters, which generate secondary high-energy particles.
The finding suggests these processes enriched galaxy cluster environments with energetic particles far earlier than previously confirmed, offering a rare glimpse into conditions shortly after cluster formation.
As future instruments like the Square Kilometer Array (SKA) come online, researchers anticipate detecting even fainter signals, deepening our understanding of cosmic magnetism, particle interactions, and the evolution of galaxy clusters.
"We are just scratching the surface of how energetic the early Universe really was," Hlavacek-Larrondo said. "This discovery gives us a new window into how galaxy clusters grow and evolve, driven by both black holes and high-energy particle physics."
Research Report:A Radio Mini-Halo in a Massive Cool Core Cluster of Galaxies at z = 1.709
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