Plate Nº 41 · recorded November 12, 2026
Space & AstronomyReported finding
Crowded Galaxies Lose Up to 80 Percent of Their Star-Forming Gas
Galaxies in a dense group seven billion light-years away hold only 20–40 percent of the star-forming gas of isolated peers, astronomers report in Astronomy & Astrophysics.
By Priya Raman3 min read603 words
In brief
- Galaxies in the crowded group held only 20–40 percent as much star-forming gas as isolated comparable galaxies.
- The studied group, COSMOS-Gr30, lies about seven billion light-years away and contains at least 44 galaxies.
- Findings were published in Astronomy & Astrophysics by a team led by the University of Strasbourg.
- Radio telescopes in France and Spain detected carbon monoxide signals used to trace cold molecular gas.
Galaxies packed into a crowded region of space hold only 20 to 40 percent as much star-forming gas as comparable galaxies living in isolation, according to an international team led by researchers at the University of Strasbourg. The finding, published in the journal Astronomy & Astrophysics, offers a clearer picture of how a galaxy's surroundings can gradually slow its growth.
The team studied a group of galaxies about seven billion light-years away. That distance matters: because light takes time to travel, astronomers see these galaxies as they were when the universe was much younger, not as they are today. The group therefore serves as a window onto an era when star formation across the universe was far more active than it is now.
Why does gas matter for star birth?
Stars form when cold clouds of gas become dense enough to collapse under their own gravity. A galaxy with a shrinking supply of this fuel may eventually produce fewer new stars, even if it still contains many older ones. Cold molecular gas — hydrogen molecules chilled to the temperatures at which stars can condense — is the raw material of every stellar generation.
Astronomers have long known that star formation across the universe peaked billions of years ago and has since declined. Explaining that slowdown requires studying both what happens inside galaxies and the effects of their environments. The new results point firmly at the second factor.
Galaxies often gather in groups and clusters. In these crowded settings, two mechanisms can attack a galaxy's gas reserves:
- Close encounters between galaxies can disturb and destabilize their gas.
- Hot material filling the space between galaxies can strip gas away or block fresh supplies from reaching individual members.
What did the researchers actually measure?
The Strasbourg-led team focused on a dense group called COSMOS-Gr30, which contains at least 44 galaxies and sits where several large structures of the cosmic web — the vast filamentary network of matter spanning the universe — intersect. That junction makes it an especially promising place to study environmental effects.
Using radio telescopes in France and Spain, the researchers searched for signals from carbon monoxide molecules. Astronomers use these radio signals as a tracer: carbon monoxide is easier to detect than molecular hydrogen, so its abundance allows them to estimate how much cold molecular gas is available for making stars.
Earlier observations of the same group had already found a large cloud of ionized gas — gas stripped of electrons and electrically charged — floating in the space between the galaxies. Taken together, the two measurements suggest that the crowded environment may be removing or disrupting the fuel that individual galaxies need to keep forming stars.
How solid is the conclusion?
The study carries clear limitations, and the researchers acknowledge them. It covers one particularly dense group, so its results should not automatically be applied to every galaxy environment. Denser-than-average regions plausibly exert stronger effects than typical ones.
Observations of more groups will help determine how common this gas-loss process is and how strongly it shapes the history of star formation. Comparing galaxies across different ages and environments can also reveal whether the loss of gas happens quickly, during brief encounters, or gradually over long periods. That distinction remains open.
What the work does establish is a documented example of a galaxy group losing its star-making gas at a time when the universe was still much younger than it is today. Each such example narrows the search for the mechanism behind the long, cosmic decline of star formation.
Seven billion years later, the light carrying that evidence has arrived.
via knowridge.com (Source)
More from Priya Raman
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Senior reporter covering people, launches and day-to-day practice in general science news at SciBeat.
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