NASA's Chandra Observes Radio Wave Formation in Colliding Galaxy Clusters

Astronomers used NASA's Chandra X-ray Observatory to study a formation of radio waves nicknamed the Treble Clef because it resembles the musical symbol. The researchers discovered the formation is likely caused by an outburst from a supermassive black hole, followed by a collision of two galaxy clusters.

The study was led by Andrea Botteon of the National Institute for Astrophysics in Italy. The paper was published Wednesday in the Astronomy and Astrophysics journal.

The Treble Clef lies almost directly behind the plane of the Milky Way. Stars, gas, and dust from Earth's home galaxy largely block the view from Earth. By using telescopes that can peer through the intervening material, the team identified what is responsible for the uncommon structure.

NASA's Chandra and the German eROSITA X-ray telescope found diffuse, hot gas at the location of the Treble Clef. The researchers determined the galaxy cluster is two clusters in the process of merging. Galaxy clusters are among the largest structures in the universe, containing hundreds of individual galaxies and huge reservoirs of superheated gas.

The authors concluded the Treble Clef formed in a two-stage process. First, an earlier outburst from a supermassive black hole drove clouds of charged particles and magnetic fields away at close to the speed of light. This produced bright radio waves that later faded as the particles lost energy. Next, the collision between the two clusters compressed or reenergized the cloud, which became brighter again in radio waves.

The researchers think the direct collision between the two clusters occurred a few hundred million years ago. The clusters are now moving away from each other. The resemblance to a treble clef is a case of pareidolia, the phenomenon when people see familiar shapes in random data.