A weak but intense radio signal has taken ten billion years to arrive on Earth, uncovering a secret mini-halo encircling one of the universe's farthest-known galaxy clusters.
The uncommon find provides scientists a window into the high-energy processes that formed the early universe. The mini-halo is a giant cloud of energetic particles and is twice as far away as any previously discovered, providing new insight into how galaxy clusters form.
A Glimpse Of The Early Universe
The finding, which is being published in The Astrophysical Journal Letters, reveals that galaxy clusters have been immersed in high-energy particles for the vast majority of cosmic time.
Scientists detected the signal while observing a galaxy cluster named SpARCS1049 with the Low Frequency Array (LOFAR) telescope, which boasts more than 100,000 antennae scattered across Europe.
The radio glow does not originate from galaxies or stars but from a billion-billion-light-year-long cloud of charged particles and magnetic fields.
"It's like discovering a giant cosmic sea full of energy," commented Julie Hlavacek-Larrondo, co-leader of the study at Université de Montréal.
Her co-lead, Durham University's Roland Timmerman, said, "To detect this signal at such a distance is incredible. It indicates these energetic processes were influencing the universe much earlier than we had believed."
What Produces A Mini-Halo?
Scientists propose two reasons for the mini-halo.
One explanation hypothesises supermassive black holes at galaxy centres expelling jets of high-energy particles into space. Yet, how such particles are able to go so far and still possess energy is unknown.
The second hypothesis suggests cosmic collisions. High-speed particle collisions in the hot plasma of the galaxy cluster can form clouds of energetic particles that can be observed from Earth.
This find verifies that galaxy clusters were full of these particles much earlier than thought.
Unveiling More of the Universe's Secrets
The mini-halo gives astronomers a unique opportunity to observe how galaxy clusters developed after they formed.
It also evokes more profound questions on the contribution of black holes, magnetic fields and cosmic rays towards fuelling galaxy clusters over billions of years.
Future telescopes, including the Square Kilometre Array (SKA), are expected to reveal even fainter signals, helping researchers map the energetic history of the cosmos.
“We’re just beginning to understand how powerful the early universe really was,” said Hlavacek-Larrondo. “This is a vital step in uncovering how galaxy clusters evolve and how the cosmos stays energised over time.”
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