In 2024 a shockwave rippled through the astronomical world, shaking it to the core. The disturbance didn’t come from some astral disaster at the solar system’s doorstep, however. Rather it arrived via the careful analysis of many far-distant galaxies, which revealed new details of the universe’s evolution across eons of cosmic history. Against most experts’ expectations, the result suggested that dark energy —the mysterious force driving the universe’s accelerating expansion—was not an unwavering constant but rather a more fickle beast that was weakening over time.

The shocking claim’s source was the Dark Energy Spectroscopic Instrument (DESI), run by an international collaboration at Kitt Peak National Observatory in Arizona. And it was so surprising because cosmologists’ best explanations for the universe’s observed large-scale structure have long assumed that dark energy is a simple, steady thing. But as Joshua Frieman, a physicist at the University of Chicago, says: “We tend to stick with the simplest theory that works—until it doesn’t.” Heady with delight and confusion, theorists began scrambling to explain DESI’s findings and resurfaced old, more complex ideas shelved decades ago.

In March 2025 even more evidence accrued in favor of dark energy’s dynamic nature in DESI’s latest data release—this time from a much larger, multimillion-galaxy sample. Dark energy’s implied fading, it seemed, was refusing to fade away.

This extensive catalog spanning 11 billion years of cosmic history allows scientists to compare ancient galaxy structures with more recent ones, revealing evolutionary patterns in galaxy groups and their brightest central galaxies. The observations show a dramatic transformation: distant galaxies from the early universe appear irregular with active star formation, while those closer to our time have “quenched” star formation and developed more organised elliptical or spiral structures.

This groundbreaking JWST survey marks the beginning of a new era in understanding galactic evolution. With 1,700 galaxy groups identified across nearly the entire history of our universe, astronomers now have an unprecedented roadmap for further investigation. Future studies will explore the physics driving these transformations—from dark matter’s role in structural formation to how supermassive black holes influence their host galaxies. As researchers analyze this rich data, we can expect significant revisions to existing theories about galaxy formation and evolution.