Nearly 10 billion years ago, an invisible tide of charged particles began bathing one of the earliest galaxy clusters in the universe. Astronomers have now detected a “mini halo” surrounding SpARCS1049, marking the most distant example ever found and doubling the previous record.
Mini halos are clouds of highly energetic particles and magnetic fields that glow faintly in radio waves. Until now, astronomers thought these structures only emerged in mature, nearby clusters. But a team co-led by Julie Hlavacek-Larrondo of Université de Montréal and Roland Timmerman of Durham University uncovered a diffuse radio signal that could only come from a sprawling sea of energized particles some 10 billion light-years away.
Using the Low Frequency Array (LOFAR)—a vast network of over 100,000 antennae stretching across eight European countries—the researchers aimed their telescopes at SpARCS1049 and spotted a radio glow spanning more than a million light-years. They confirmed that the signal did not originate from individual galaxies but from the space between them, where a mini halo lies hidden.
“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.
Two processes may explain how this ancient halo formed. One involves supermassive black holes at a cluster’s center spewing jets of particles that then drift outward. The other points to collisions among charged particles in the hot plasma, smashing into each other at near-light speeds and energizing the surrounding void.
“It’s astonishing to find such a strong radio signal at this distance,” said Timmerman. “It means these energetic particles and the processes creating them have been shaping galaxy clusters for nearly the entire history of the universe.”
This discovery offers a rare glimpse of the early cosmos, revealing that high-energy physics played a role in shaping colossal structures almost as soon as they formed. With next-generation observatories like the Square Kilometre Array on the horizon, astronomers hope to uncover even fainter echoes of the universe’s energetic youth.
“We are just scratching the surface of how energetic the early Universe really was,” said Hlavacek-Larrondo.
The study has been accepted in Astrophysical Journal Letters, with the pre-print version of the paper published.
