Research Highlights

Radio signals from a distant galaxy find their way to Earth

doi:10.1038/nindia.2020.31 Published online 18 February 2020

An artist’s animation of galaxy with jets from a supermassive black hole.


Indian astrophysicists have discovered relic radio signals that are emanating from the edge of a distant low-mass galaxy cluster named Abell 16971.

Stemming from a merger of two galaxy clusters, such radio signals provide a unique opportunity to study matter and galaxy cluster physics that cannot be explored in laboratories.   

Since the Big Bang, galaxy cluster mergers are the most energetic events in the universe. Behaving like particle accelerators, such mergers release tremendous energy and accelerate electrons close to the speed of light, eventually generating tsunami-like shock waves. These waves then reach the edge of clusters and emit relic radio signals.

Relics are common in massive merging clusters. But only a few relics have been detected in low-mass clusters. 

While scanning the Northern Sky with the LOFAR Two-metre Sky Survey (LoTSS), an array of radio telescopes, the scientists from the Savitribai Phule Pune University and the National centre for radio Astrophysics of Tata Institute of Fundamental Research, both in Pune, India, accidentally discovered Abell 1697. They observed that the cluster is moving away from us. The cluster is home to 84 galaxies.  

Radio and optical images reveal that the radio emission from the cluster is purely diffuse in nature. Survey provides reasonable evidence that the structure is a peripheral relic. The diffuse radio emission has very low surface brightness.

Analysis indicates that the radio emission is a radio phoenix, a special type of relic radio signal generated by fossil electrons from the past events of radio galaxies.


1. Paul, S. et al. Radio-relic and the diffuse emission trail discovered in a low mass galaxy cluster Abell 1697. Astron. Astrophys. 633, A9 (2020)