# INAF astronomers identify Treble Clef radio source as a 2.5-million-light-year radio phoenix

- Published: 2026-11-09 00:54 UTC
- Section: Sky & Space › Astronomy
- Tags: Treble Clef, VLSS J0318.9+5755, radio phoenix, galaxy cluster merger, supermassive black hole, LOFAR, GMRT, Chandra X-ray Observatory, SRG/eROSITA, Astronomy & Astrophysics
- URL: https://realtech.media/news/rt-0c3c7d87c1f4e860bb7810f4_inaf_astronomers_identify/

**The source VLSS J0318.9+5755, hidden behind the Milky Way's dust disk, is old plasma re-energized by shocks in a galaxy cluster merger, according to the authors.**

![INAF astronomers identify Treble Clef radio source as a 2.5-million-light-year radio phoenix](https://realtech.media/media/2026/11/1bafab22300e1cc4.jpg)
*Serge Yerin (YeS), Wikimedia Commons, CC BY 4.0*

A team led by Andre Botteon of the Italian National Institute for Astrophysics (INAF) has confirmed the nature of the radio source VLSS J0318.9+5755, which lies behind the dust disk of the Milky Way, according to ixbt.com. [1] The object, informally called Treble Clef for its shape, is neither a pulsar nor a local gas cloud. It is a giant remnant of an ancient burst of activity from a supermassive black hole at the center of a colliding galaxy cluster. [1]

The study draws on low-frequency surveys by the Low Frequency Array (LOFAR) and observations by the Giant Metrewave Radio Telescope (GMRT). It also uses X-ray images from the Chandra X-ray Observatory and the SRG/eROSITA satellite. [1]

## Radio phoenix in a merging cluster

The cluster is about 1.5 billion light-years from Earth, and the radio source extends over 2.5 million light-years. [1] Astronomers classified it as a "radio phoenix": cooled plasma that was re-heated by shock waves from the merger of two galactic structures. The age of the revived emission is estimated at 190–200 million years. [1]

## Two stages of formation

The structure formed in two steps. First, jets from the central black hole pushed out clouds of charged particles and magnetic fields at speeds close to the speed of light, producing bright radio emission that faded as the particles lost energy. [1] Later, the collision of the clusters created conditions for compression and re-injection of energy into the old plasma. Shock waves, similar to the sound barrier of supersonic aircraft, probably played a key role in restarting the glow and making the object visible again to present-day radio instruments. [1]

The source was recorded as early as the 1960s but was long considered an artifact or a pulsar because of its position near the plane of the Galaxy. In 2004, astronomers hypothetically linked it to a galaxy cluster, but detailed observations were lacking until multiwavelength survey data became available. [1]

The results have been accepted for publication in Astronomy & Astrophysics. The next steps include searching archives of low-frequency radio observations for similar objects, to estimate the share of such revived structures among galaxy clusters. [1]

## Sources

1. [ixbt.com](https://www.ixbt.com/news/2026/11/08/kosmiceskii-feniks-za-pylevym-diskov-mlecnogo-puti-obnaruzen-gigantskii-radiogalakticeskii-obieekt.html)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-0c3c7d87c1f4e860bb7810f4_inaf_astronomers_identify/