A Galaxy Born In A Crowded Corner Of The Universe Faces A Very Different Future Than One Born Alone

NASA’s Webb Telescope Finds That Location Has Always Been Everything, Even for Galaxies

Real estate wisdom holds that location is everything. For galaxies, it may be even more fundamental than that. A sweeping new study using the most powerful space telescope ever built has charted the cosmic web, the vast invisible scaffolding of filaments, clusters, and voids that gives the universe its large-scale structure, and tracked how a galaxy’s position within that web is closely linked to its development across roughly 13 billion years of cosmic history, from the Epoch of Reionization, when some of the earliest galaxies were already taking shape about 800 million years after the Big Bang, to the present.

Published in The Astrophysical Journal, the research draws on NASA’s James Webb Space Telescope and a selected sample of 164,000 galaxies from the COSMOS-Web survey, the largest survey the telescope has ever conducted. Where a galaxy lives in the cosmic web is closely linked to how massive it becomes, how fast it forms stars, and when it stops forming stars altogether.

This kind of cosmic census has been attempted before, but never with this depth or reach. Earlier surveys struggled to detect faint, lightweight galaxies at great distances, leaving the picture incomplete, much like trying to understand a city’s economy by surveying only its wealthiest residents. COSMOS-Web changes that, letting astronomers see smaller, dimmer galaxies farther back in time than ever before.

NASA Maps a Universe Full of Neighborhoods

The universe is not a uniform sea of galaxies. It resembles a vast metropolis, with dense downtown clusters connected by filament highways, surrounded by enormous empty regions called voids. Galaxies aren’t scattered randomly; they cluster along these filaments and at their intersections, like beads on a three-dimensional web.

To reconstruct this structure, the research team measured each galaxy’s brightness across multiple wavelengths and used those measurements to estimate distance. From that data, they built detailed density maps showing where galaxies crowd together and where they thin out, across a patch of sky spanning roughly the area of a few full moons placed side by side, and across billions of years of cosmic time.

One important caveat: these maps rely on color-based distance estimates rather than more precise spectroscopic measurements, and the team treats a lookback time corresponding to roughly 13 billion years as the practical ceiling for reliable density mapping.

At one representative distance slice, COSMOS-Web captured more than 7,400 galaxies compared to fewer than 1,900 in the previous leading catalog, letting researchers detect cosmic structures that were previously invisible. The survey reaches about 80% mass completeness down to galaxies of roughly 500 million solar masses at the farthest distances examined, a first for wide-area surveys of this kind.

Dense Cosmic Regions Grew the Heaviest Galaxies Earliest

One of the study’s clearest findings is that heavier galaxies tend to live in denser parts of the cosmic web, and this holds at every point in cosmic history the researchers examined.

Galaxies in overdense regions with above-average crowding tend to be two to four times more massive than those in average or underdense environments. This is consistent with how structure is thought to form: the densest knots in the early universe were sites of the fastest, most turbocharged galaxy construction. Dense early regions, the seeds of what would later become today’s massive galaxy clusters, were places where galaxies rapidly assembled their mass before the rest of the universe caught up.

The pattern is especially pronounced in galaxies that have gone quiet, having stopped forming new stars. For these retired star factories, the link between dense environments and higher mass is strongest in the more recent universe. At earlier cosmic times, that connection appears only in the most extremely crowded environments, consistent with early mass assembly concentrated in protocluster regions.

How a Crowded Neighborhood Eventually Shuts Galaxies Down

Perhaps the most arresting finding concerns star formation itself, and specifically how the relationship between environment and star-building activity reverses over time.

In the young universe, galaxies in denser environments were actually forming stars at higher rates than their counterparts in emptier regions. Cold gas was abundant, filaments fed growing protoclusters with fresh fuel, and frequent galaxy collisions could trigger bursts of star formation.

Over time, those same conditions increasingly became a death sentence for star-making activity, particularly in smaller, lower-mass galaxies. Processes likely responsible include ram pressure stripping, where a galaxy’s gas supply is blasted away as it plows through hot cluster gas, and strangulation, where the fresh supply of cold gas from cosmic filaments is gradually cut off. Energy released by growing supermassive black holes can also heat or expel a galaxy’s gas from the inside. By the present epoch, dense environments tend to suppress star formation in low-mass galaxies rather than fuel it.

The research also found a clear progression in what drives star formation to stop. In the early universe, a galaxy’s own mass was the dominant factor, with more mass meaning more internal feedback capable of shutting star formation down. In a middle period of cosmic history, mass and environment played roughly equal roles. In the more recent universe, for small low-mass galaxies, the surrounding environment has become the stronger force driving them to go quiet.

Across virtually the entire observable history of the universe, a galaxy’s cosmic address appears to be one of the most consequential facts about it.

---