NASA Confirms How Our Galaxy and Other Disk Galaxies Took Shape

Groundbreaking observations align with long-standing "inside-out" formation theory

For decades, astrophysicists theorized that disk galaxies like our Milky Way formed "inside-out"—starting as dense cores before slowly expanding their spiral arms over billions of years. Now, NASA’s James Webb Space Telescope (JWST) has delivered decisive evidence confirming this model, fundamentally reshaping our understanding of galactic evolution.

The breakthrough emerged from JWST’s unprecedented infrared observations of distant, ancient galaxies. By peering back to when the universe was just 1–2 billion years old, astronomers detected early galactic cores brimming with old stars—exactly as predicted by simulations. These dense cores acted as gravitational anchors, gradually accumulating gas and dust to form sprawling disks and spiral structures.

"Webb’s data closes a decades-old knowledge gap," said Dr. Erica Nelson, a lead researcher on the study. "We’re seeing galactic nurseries evolve exactly where and how our models suggested."

Key Evidence from Cosmic Dawn
The JWST findings, detailed in NASA’s mission report, reveal that nascent galaxies produced stars 10–20 times faster in their cores than their outer edges early in cosmic history. This imbalance created the mass gradient needed for disks to later develop. Supporting simulations, published in the Monthly Notices of the Royal Astronomical Society, show how stellar feedback and dark matter shaped these dynamics.

Critically, Webb observed galaxies too distant and faint for prior telescopes to resolve. Their light, stretched by cosmic expansion into infrared wavelengths, exposed chemical signatures proving stars in galactic centers formed earlier and from primordial gas, while outer stars emerged later from enriched material—a hallmark of inside-out growth.

Why It Matters

This confirmation anchors our Milky Way’s origin story. "We’re literally seeing how our galactic home was built," Nelson emphasized. The model also explains why younger stars populate spiral arms while ancient stars dominate galactic cores—a pattern now observed across thousands of galaxies.

For astronomy enthusiasts seeking deeper context, astrophysicist Neil deGrasse Tyson’s Astrophysics for People in a Hurry offers accessible insights into galactic evolution and the tools unlocking these discoveries.

Looking Ahead

While the inside-out model now stands validated, mysteries remain: How did early gas clouds collapse so efficiently? What role did black holes play? JWST’s future observations aim to explore these questions, potentially revealing even earlier phases of galaxy formation.

"Every answer births new questions," Nelson noted. "But for the first time, we’ve watched the universe’s grandest architectures grow from blueprints to reality."

*Image: JWST’s NIRCam view of galaxy cluster MACS0647—a lens into early galactic structure/NASA, ESA, CSA*