Astronomers using the James Webb Space Telescope have measured the most powerful gas outflow ever recorded from a “dead” galaxy outside our cosmic neighborhood and found that even outflows this extreme may not be enough to permanently shut down star formation.
Studying 23 massive, quiescent galaxies from roughly 11–13 billion years ago, researchers traced neutral gas being blown outward using a specific absorption signature in their light, detecting outflows in many of them. Their paper was published in Astronomy & Astrophysics on Aug. 14.
Galaxy regulators
As matter falls into supermassive black holes, it releases huge amounts of energy that can drive powerful winds or outflows from the galaxy’s center. These outflows can heat and expel gas, stir up star-forming material and prevent new stars from forming. They can also cut off the gas supply to the black hole, helping regulate how galaxies evolve. Studying these outflows directly is key to understanding how galaxies die or “quench.”
Most outflow studies measure hot, ionized gas, but cool, neutral gas traced by the sodium “Na I D” absorption doublet often carries far more of the total outflow mass.
“In galaxies with both neutral and ionized outflows, the neutral outflow rates are typically 10–100 times higher than the ionized outflow rates,” researchers explain in the paper. “JWST/NIRSpec has now enabled direct detections of Na I-traced outflows well beyond the local universe.”
Tracing sodium
Led by Pengpei Zhu of the Cosmic Dawn Center (DAWN) in Copenhagen, this study focuses on 23 massive quiescent galaxies—galaxies that have stopped forming new stars—taken from a JWST survey program called DeepDive, across a redshift range of 2.82–4.62. This translates to when the universe was roughly 1.3–2.3 billion years old.
Searching for sodium signatures in galaxies, the researchers first removed the sodium absorption produced by stars themselves using detailed models of the galaxies’ stellar populations. Using thousands of simulated noise tests, they made sure the detected signals were real.
For confirmed outflows, they modeled the absorption to measure the gas velocity, density and how much of the galaxy the outflow covers. These measurements were then used to calculate the mass of gas being expelled.
Finally, they compared the outflow speeds with each galaxy’s escape velocity to determine whether the gas could escape or eventually fall back. Among these 23 ancient dead galaxies, they detected excess Na I D absorption in 13. Seven of the 23 showed clear blueshifted absorption, which means the gas is moving toward us and away from the galaxy.
Not completely dead?
In every Na I-detected galaxy, the outflow rate was found to exceed the galaxy’s ongoing star-formation rate. However, they found that most of the outflowing gas is not moving fast enough to actually leave the galaxy forever. The gas is more likely to fall back into the galaxy like a fountain in a few million to hundreds of millions of years.
Once the gas is replenished, star formation may reignite. “Since most outflows are not likely to escape, their direct role in quenching or maintaining quiescence is uncertain,” researchers write. “They likely represent short-lived fountain cycles rather than ejective quenching events.”
In particular, one galaxy, DD-236, stood out with the most extreme gas outflow rate ever measured beyond the nearby universe. Its outflow was accompanied by signs of an actively feeding black hole at its center.
The team is not yet sure what mechanism is driving these outflows. The link between black hole activity and these outflows is not well established. Only two of 13 galaxies with outflows show signs of actively feeding black holes, while two confirmed active black holes show no outflow. However, the two most extreme outflows are linked to active black holes.
“Their origins are not directly tied to ongoing AGN activity or the most recent starbursts, but they do potentially reflect a mix of past AGN activity and ongoing mergers,” they conclude.
Written for you by our author Shreejaya Karantha, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive.
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Publication details
Pengpei Zhu et al, There and back again: Neutral outflows in z ∼ 3.5 quiescent galaxies, Astronomy & Astrophysics (2026). DOI: 10.1051/0004-6361/202659510
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Webb measures extreme gas outflows from distant ‘dead’ galaxies (2026, September 16)
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