The cosmic architecture of galaxies is built through violent collisions

Nature · Published 3 October 2026 Swipe more like this →

In short: Beyond the shimmering clouds of color lies a complex engine of gravity. Galaxies are not static islands, but dynamic collections of stars, gas, dust, and dark matter. From the smallest clusters to the massive structures of the cosmic web, their shapes are forged by billions of years of celestial movement.

Galaxies emerge from small, swirling clouds of dust and stars. As these clouds approach one another, gravity pulls them into collisions, knitting them into larger, spinning structures. These interactions are not merely destructive; subsequent collisions can fling material toward the edges of a galaxy, helping to create the expansive spiral arms that host vast colonies of stars.

The scale of these structures varies immensely. While some small galaxies span only a few hundred light-years and contain a few thousand stars, the largest can exceed a million light-years across and house trillions of stars. Most large galaxies are anchored by supermassive black holes at their centers, some possessing a mass billions of times greater than our Sun.

The Milky Way, our home, is a spiral galaxy with a disk stretching more than 100,000 light-years. It resides within the Local Group, a neighborhood of over 50 galaxies, including our nearest large neighbor, Andromeda. This group is part of the even larger Laniakea supercluster. While galaxies can organize into groups of 100 or fewer members, they also form massive clusters and superclusters that comprise the cosmic web.

Timing is also a factor in this cosmic evolution. Most galaxies are estimated to be between 10 billion and 13.6 billion years old, approaching the age of the universe itself, which formed roughly 13.8 billion years ago. Even in the modern era, astronomers have identified a galaxy thought to have formed approximately 500 million years ago.

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