Astronomers have detected a vast cloud of energetic particles — a ‘mini-halo’ — around one of the most distant galaxy clusters, according to a new study. This mini-halo lies so far away that its light takes about 10 billion years to reach Earth, making it the most distant mini-halo ever discovered to date and doubling the previous distance record. The finding suggests that even in the very early universe, massive galaxy clusters were already filled with high-energy particles. The international research team was co-led by Julie Hlavacek-Larrondo and Roland Timmerman.

Faint radio glow reveals mini-halo

According to the study, the team used the European Low Frequency Array (LOFAR) radio telescope to study the distant cluster SpARCS1049. LOFAR – a network of over 100,000 antennas spread across eight European countries – captured an extremely faint, diffuse radio signal surrounding the cluster. This glow stretches over a million light-years, revealing a giant “mini-halo” of high-energy particles and magnetic fields.

Analysis showed the emission filled the space between galaxies rather than coming from any single galaxy. The cluster’s light took 10 billion years to reach us, doubling the distance record for any known mini-halo. Co-leader of the reasearch Julie Hlavacek-Larrondo describes it as a vast cosmic ocean,in which entire galaxy clusters are constantly immersed in high-energy particles.

Origins of the mini-halo

Two main theories exist for the mini-halo’s origin. One possibility is that powerful jets from supermassive black holes in the cluster’s galaxies have injected the energetic particles into space. However, it is unclear how such particles could travel far from the galaxy centers without losing their energy.

Another idea is that collisions within the cluster’s hot gas create the particles. In this scenario, charged particles in the intracluster plasma crash at near-light speeds, producing the observed high-energy particles. These observations imply that massive clusters were already filled with energetic particles very early on. Future instruments like the Square Kilometre Array (SKA) will find even fainter mini-halos, helping scientists study the roles of magnetic fields and cosmic rays in cluster evolution.