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

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 .