Galaxies, like people, go through phases. Thanks to the incredible vision of the James Webb Space Telescope (JWST), scientists have now discovered that galaxies—yes, even our own Milky Way—had a thick, messy “teen” phase before settling into the slim, calm shapes we see today.

A team of international astronomers analyzed 111 galaxies seen edge-on (side view) using JWST, revealing how galaxies have evolved over billions of years. The results? Most galaxies started off thick and turbulent, forming a “thick disk” of stars, and only later developed the thinner, more organized disks we see in many spiral galaxies today.

Galactic Fossils Tell a Story

The structure of galaxies holds clues about their history. Our Milky Way, for example, has two main components in its disk:

A thin disk, filled with younger stars rich in elements like oxygen and carbon.

A thick disk, made of older, more primitive stars.

These two layers act like fossil records, helping astronomers understand how stars—and the elements they create—formed and evolved over time.

Before JWST, astronomers could only study this layered structure in nearby galaxies. Distant ones were too blurry and faint. But JWST, launched in 2021, changed everything.

Seeing the Past with New Eyes

By looking at galaxies as far as 10 billion light-years away (that’s like peering into the universe’s teenage years), scientists could finally see how galaxies looked when they were young.

Lead researcher Takafumi Tsukui says, “It’s like using a time machine. We’re seeing galaxies forming their disks in real-time—just billions of years ago.”

What they found was striking: early galaxies mostly had a thick disk. Over time, a thin disk formed inside it. In bigger galaxies, this thin disk showed up earlier—likely because they were better at turning gas into stars quickly.

The Milky Way Is Not So Special After All

For years, astronomers wondered if the Milky Way’s structure—thick disk outside, thin disk inside—was a cosmic oddball. This study says otherwise. Many galaxies, even ones very far away, follow the same pattern.

The process seems to go like this:

In the early universe, galaxies are chaotic, gas-rich, and full of turbulence.

That turbulence leads to intense star formation, creating a thick disk.

As stars form and the galaxy evolves, the gas settles down.

A thin, calm disk forms within the thick one.

Why It Matters

Understanding how galaxies grow helps us understand where stars—and the building blocks of life—come from. Elements like carbon and oxygen, essential for life, are created inside stars. So the story of galaxy evolution is also the story of how we got here.

And thanks to JWST, we now know that the Milky Way’s journey—from thick to thin—is part of a much bigger story across the universe.