How Young Stars Sculpt Their Galaxies: PHANGS Survey Maps 18,000 Star-Forming Regions with JWST, Hubble, and ALMA

Astronomers have long known that young stars don't just form within galaxies — they actively reshape them. But the details of this process have remained murky. Now, a sweeping new study from the PHANGS collaboration has brought the picture into sharp focus, analyzing roughly 18,000 star-forming regions across 19 nearby galaxies using the combined power of the James Webb Space Telescope (JWST), the Hubble Space Telescope, and the Atacama Large Millimeter/submillimeter Array (ALMA) .

The findings, presented at the 248th meeting of the American Astronomical Society on June 17, 2026, reveal how newborn massive stars drive the expansion of their birth clouds through stellar feedback, and show that the strength and outcome of this process depend dramatically on the surrounding galactic environment .

The Core Discovery: Stellar Feedback Drives Gas Expansion

The main finding is that pressure from ionized gas generated by newborn massive stars pushes interstellar material outward, driving the expansion of star-forming regions . This feedback process can either trigger new star formation by compressing surrounding gas or shut it down entirely by dispersing the gas needed for stellar birth .

The ionized gas is brightest in the shells of expanding bubbles and coincides with the youngest — roughly 1 million years old — and most massive — about 10⁵ solar masses — stellar associations . This direct correlation provides strong evidence that these young, massive stars are the engines driving the expansion.

A Tale of Two Galaxies: Environment Matters

Whether star-forming regions continue to grow or stall depends strongly on their surrounding environment . In normal spiral galaxies like the Milky Way, the feedback process is relatively orderly. But in more extreme systems, conditions change dramatically.

The study highlights the extreme case of NGC 3256 — a collisional starburst system located about 100 million light-years away in the constellation Vela, formed from the collision of two separate galaxies . Studied via the Great Observatories All-Sky LIRG Survey (GOALS), NGC 3256 presents a very different picture .

Feedback pressures in NGC 3256 are about 100 times stronger than in Milky Way-like spiral galaxies . This creates a much more turbulent and unpredictable environment where the gas is not settled in a simple flat disk . Young massive star clusters in the densest regions are confined by this intense pressure, but most clusters remain powerful enough to continue expanding .

The molecular gas in NGC 3256 is extreme by every measure: its giant molecular clouds show median velocity dispersions of 23 km/s, mass surface densities of 470 M☉ pc⁻², and internal turbulent pressures an order of magnitude higher than those in normal disk galaxies .

Hidden in Plain Sight: Dust-Enshrouded Young Star Clusters

A companion study by Sajia Shahrin Neha used JWST's NIRCam and MIRI instruments, imaging at 2 to 21 micrometers, to study young, dusty compact sources in nearby galaxies . The study revealed previously hidden young massive star clusters (YMCs) that were completely buried in cosmic dust and invisible to earlier optical surveys .

These dust-enshrouded YMCs represent the earliest phases of cluster formation — a stage that JWST's infrared capabilities are uniquely able to detect . In NGC 3256 alone, JWST identified 116 such heavily obscured YMCs, increasing the known sample of dust-enshrouded massive star clusters by an order of magnitude compared to earlier Hubble studies . The data suggest a rapid dust-clearing timescale of less than 3-4 million years for these emerging clusters .

Broader Implications: A Benchmark for Galactic Evolution Models

The team concluded that these measurements provide physical conditions that "haven't been able to study before" and offer a critical benchmark for improving models of how galaxies evolve across different environments .

The findings help explain how young stars influence their host galaxies long before dramatic events like supernova explosions occur, and show that feedback models must account for environmental context — from quiet spirals to violent mergers . Combined with the discovery of buried clusters, this work gives astronomers a more complete census of star formation, filling in the earliest, most dust-obscured phases that were previously invisible.

What's Next

The PHANGS-JWST Treasury Survey continues to collect data, with plans to produce a full inventory of star formation, accurate mass and age measurements of star clusters, and detailed maps of how stellar feedback alters the interstellar medium across a wide range of galactic environments .