From tiny clusters to cosmic webs, galaxies define our universe

Space · Published 25 October 2026 Swipe more like this →

In short: Galaxies are more than just collections of stars; they are massive structures bound by gravity that span millions of light-years. From the smallest dwarf systems to the sprawling cosmic web, these celestial bodies reveal the fundamental architecture of our existence and the history of the cosmos.

Gravity binds together massive clouds of dust and gas alongside planets and stars to form galaxies. They exhibit a staggering range in scale: the largest can contain trillions of stars and stretch across more than a million light-years, while the smallest may house only a few thousand stars spanning just a few hundred light-years. Most large galaxies are anchored by supermassive black holes at their centers, some reaching masses billions of times that of our Sun.

The universe's galactic architecture is organized hierarchically. Mutual gravitational forces often pull smaller collections of roughly 100 or fewer members into groups. These can further organize into clusters containing thousands of galaxies. On an even larger scale, these structures form superclusters, which are not gravitationally bound but contribute to the cosmic web—a vast network of matter featuring 'walls' of galaxies and empty voids.

Our own home, the Milky Way, is a spiral galaxy with a disk spanning more than 100,000 light-years. Earth sits along one of its spiral arms, roughly halfway from the center. It takes our solar system approximately 240 million years to complete a single orbit around this galactic center. The Milky Way resides in the Local Group, a neighborhood of over 50 galaxies including the Andromeda galaxy and various dwarf galaxies.

The timeline of these structures is nearly as old as time itself. With an age ranging from 10 billion to 13.6 billion years, many galaxies nearly date back to the universe's birth at 13.8 billion years ago. Conversely, astronomers believe the youngest known galaxy formed only about 500 million years ago.

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