Six Galaxies, One Shared Destiny: A Glimpse 12 Billion Years into the Past

The radiation from TGSS J1530+1049 travelled for more than 12 billion years before reaching Earth. We therefore observe the source as it existed when the Universe was only around 1.5 billion years old—barely one tenth of its present age. Interestingly, the galaxy's distance had previously been overestimated. Based on the discovery observations reported in 2018, researchers initially inferred a much higher redshift (z ≈ 5.7), placing the object in an even earlier epoch of cosmic history. New spectroscopic observations with the James Webb Space Telescope (JWST) have since refined the measurement to z≈4, corresponding to a Universe approximately 1.5 billion years old.

These extremely distant objects, known as high-redshift radio galaxies (HzRGs), are among astronomers' favourite cosmic time capsules. They provide a unique opportunity to observe how the first galaxy clusters and giant galaxies began to emerge only a few hundred million years after the Big Bang.

Radio Telescopes and the James Webb Space Telescope Join Forces

The study combined two complementary observational techniques.

On the radio astronomy side, the team led by Krisztina Éva Gabányi used two of the world's most sensitive radio interferometer arrays—the European VLBI Network (EVN) and the UK's e-MERLIN array, including the 76-metre Lovell Telescope—to map the morphology and positions of the radio-emitting structures at the galaxy's centre with milliarcsecond resolution.

Complementing these observations, Aayush Saxena (University of Oxford) led infrared observations with the NASA/ESA/CSA James Webb Space Telescope, mapping both the ionised gas surrounding the system and the galaxies embedded within it. Together, these two independent datasets provide a remarkably complete picture of the processes unfolding around the young active galactic nucleus.

The findings were published in two peer-reviewed papers in 2026. Aayush Saxena and collaborators reported the JWST results in the Open Journal of Astrophysics, while Krisztina Éva Gabányi and colleagues presented the radio observations in Astronomy & Astrophysics.

Not One Galaxy but Six: The Core of a Protocluster Taking Shape

One of the study's biggest surprises came when the JWST revealed that the radio source is not associated with a single galaxy, but with a compact system of at least six galaxies converging within a region only a few tens of thousands of light-years across. Four of the six galaxies are already massive in their own right, with a combined stellar mass of several hundred billion times that of the Sun.

Such young assemblages of galaxies are known as protoclusters—the ancestors of the vast galaxy clusters that today contain thousands of member galaxies. According to the researchers, they have captured a rare moment in cosmic history, when the future members of a galaxy cluster still exist as separate galaxies but are already in the process of merging into a larger structure. Remarkably, the system closely resembles numerical simulations that model the rapid sequence of mergers through which today's brightest cluster galaxies (BCGs) are thought to have formed.

A Young Black Hole Behind the Scenes

Meanwhile, ultra-high-resolution radio observations pinpointed a supermassive black hole at the heart of one of the six galaxies—the one hosting the radio source. The black hole is actively accreting matter from its surroundings whilst simultaneously ejecting part of it back into space in the form of powerful relativistic jets.

The radio-emitting structure spans only about 17,000 light-years, a relatively modest size that suggests the galaxy's active galactic nucleus (AGN) is still very young on cosmic timescales. Astronomers classify such objects as medium-sized symmetric objects (MSOs): compact radio sources whose jets have not yet broken out of the interstellar medium of their host galaxies and which represent an early evolutionary stage of the giant radio galaxies they are expected to become.

The spatial distribution of the radio emission—elongated along a north–south axis—closely mirrors the distribution of the ionised gas detected by the JWST, although the latter extends across a much larger region, spanning nearly 75,000 light-years. This striking alignment suggests that the radio jets launched by the central black hole are interacting directly with the surrounding gas clouds, influencing their structure and motion.

Why This Discovery Matters

TGSS J1530+1049 and other extremely distant radio galaxies like it are crucial to answering two of the biggest outstanding questions in modern astrophysics: how supermassive black holes were able to grow so rapidly during the first 1.5 billion years of the Universe's history, and how the giant elliptical galaxies we observe today formed through successive mergers of smaller galaxies.

This remarkable system allows astronomers to follow two fundamental processes simultaneously: the assembly of a giant galaxy and the growth of the supermassive black hole at its centre. In effect, we are witnessing a cosmic construction project whose finished product will ultimately become the ancestor of one of the most massive galaxies in the present-day Universe.

The Hungarian contribution to the research was supported by HUN-REN and by the Hungarian National Research, Development and Innovation Office (NKFIH) through the TKP2021-NKTA-64 Excellence Programme.