Galaxies Living in Empty Space Are Smaller Than Their Neighbors

By Space.Fan Editorial DeskSeptember 18, 2026 at 4:00 AM UTC

New research shows that massive galaxies in cosmic voids have less room to grow, leaving them physically smaller than galaxies in crowded neighborhoods.

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The Drop

Space is not completely full. There are vast, empty bubbles called cosmic voids where very few galaxies exist. Astronomers recently took a close look at these quiet regions by comparing data from the Sloan Digital Sky Survey with computer models of how the universe grows. They wanted to see if living in a lonely part of space changes how a galaxy develops over time. By measuring thousands of galaxies, the team found that massive galaxies located inside these empty voids look different than those found in busier parts of space. At the same mass, void galaxies are about 11 percent more compact than those living in more crowded areas. This means these galaxies occupy less space and are more tightly packed together. The researchers figured this out by using a special tool called VoidFinder to pick out galaxies based on how much empty space was around them. They then compared this real-world data against a simulation known as TNG300, which mimics how the universe changes over billions of years. Both the actual telescope data and the computer model showed the exact same pattern: living in the middle of a void makes it harder for a galaxy to reach its full size.

Why It Matters

This discovery helps solve a puzzle about how galaxies grow. Most large, early-type galaxies get their size by crashing into and merging with other smaller galaxies over billions of years. In crowded areas, these mergers are common, allowing galaxies to build up large outer envelopes of s. In deep voids, there are very few neighbors to merge with, so that growth is suppressed. This proves that a galaxy's home address matters just as much as its mass when it comes to determining its final shape.

The Catch

While the pattern is clear, it is not the same for every galaxy in a void. The size difference only becomes obvious in the deepest parts of these empty regions. As you move toward the edges of a void where there are more galaxies, the effect fades away. Scientists also noted that this research focuses mostly on central galaxies, so it might not explain why every single galaxy in a void behaves the way it does.

Put That in Perspective

Scientists have studied galaxy clusters for decades, but looking at what happens in the emptiest parts of the universe gives us a better picture of cosmic evolution. By seeing how galaxy growth shuts down in the absence of neighbors, researchers have a clearer understanding of how late-time mergers act as a primary engine for building large galaxies.

Source September 18, 2026

Olivia Curtis, Bryanne McDonough, Tereasa G. Brainerd

ApJ·10.48550/arXiv.2609.19253