Webb reveals the hidden scars left by ancient galaxy mergers

Galaxies are often pictured as graceful islands of stars drifting through space in relative peace. Yet behind their elegant appearance lies a far more turbulent history. Throughout cosmic time, galaxies have collided, merged, and reshaped one another through powerful gravitational interactions.

Now, observations from the James Webb Space Telescope (JWST) are providing astronomers with a closer look at the consequences of these dramatic events. Researchers studying distant galaxies have identified subtle structural features that appear to be remnants of ancient collisions, offering new clues about how some galaxies abruptly stopped producing new stars.

Galaxies that stopped forming stars too early

Galaxies remain active as long as they contain enough cold gas to create new generations of stars. This gas serves as the essential material from which stars are born. However, some galaxies unexpectedly stop this process and become what astronomers refer to as «quenched» galaxies.

This phenomenon becomes even more intriguing when it is observed in the early universe. Astronomers have discovered massive galaxies that seem to have shut down their star formation surprisingly early, despite existing during a period when the universe was still rapidly evolving and building large structures.

Understanding why these galaxies ceased producing stars has become one of the important questions in modern astrophysics.

Webb reveals hidden evidence beneath smooth appearances

Thanks to its powerful infrared instruments, Webb can observe extremely distant galaxies with a level of detail that was previously difficult to achieve. By examining galaxies as they appeared billions of years ago, researchers noticed something unexpected.

Some galaxies that initially appeared smooth and stable showed faint distortions and irregular features after closer analysis. These patterns resemble long-lasting scars left behind by major gravitational interactions.

Although these galaxies may look calm today, their structures suggest that their histories were anything but peaceful.

The evidence indicates that mergers between galaxies may have played an important role in changing their evolutionary path.

When growth can become destruction

Galaxy mergers are among the most energetic events in the universe. As galaxies interact, gravitational forces can compress enormous amounts of gas and trigger intense bursts of star formation.

But these same events can create conditions that eventually shut star formation down.

Large numbers of newly formed stars, supernova explosions, and energetic feedback mechanisms can heat or expel gas from galaxies. Without a sufficient supply of cold gas, the process of creating new stars gradually comes to an end.

In a sense, galaxies may consume their own future while undergoing periods of extreme activity.

Reading the fossil record of the universe

Astronomers cannot directly watch most ancient galaxy collisions happen in real time. Instead, they reconstruct the history of these events by studying the structures left behind.

Similar to how geologists examine layers of rock to understand Earth’s past, researchers analyze distortions in galaxies to reveal events that happened billions of years ago.

As Webb continues to observe deeper regions of the universe, scientists hope to determine whether these ancient scars represent isolated cases or whether violent mergers were a common stage in galaxy evolution.

The universe can appear calm when viewed from a distance, but discoveries like these continue to reveal a more dynamic and dramatic cosmic story.

© 2026 SKYCR.ORG | Homer Dávila Gutiérrez, FRAS. All rights reserved. Reproduction in whole or in part is prohibited without express authorization. More information: Monthly Notices of the Royal Astronomical Society (2026). DOI: 10.1093/mnras/stag987