How did the Milky Way become the calm, spiral galaxy we see today?
New observations from the James Webb Space Telescope (JWST) suggest that our home galaxy had a much rougher childhood than astronomers once imagined.
In a study led by Vivian Tan, a Ph.D. graduate from York University, researchers pieced together the Milky Way’s past by studying nearly 900 “Milky Way twins.”
These are distant galaxies that closely match what scientists think the Milky Way looked like at different stages of its life.
Because light from faraway galaxies takes billions of years to reach us, looking deeper into space is like looking back in time.
By examining these galactic twins across a wide range of distances, the team reconstructed a timeline of how galaxies like the Milky Way grew and changed over billions of years.
Their findings, published in The Astrophysical Journal, show that our galaxy’s early years were anything but peaceful.
The galaxies in the study span a critical period in cosmic history, from when the universe was only about 1.5 billion years old to around 10 billion years old. This era marks a major transition, when galaxies evolved from small, messy systems into the large, organized disks we see today.
To conduct the study, the researchers combined data from JWST and the Hubble Space Telescope.
They used a clever natural trick called gravitational lensing, where massive galaxy clusters act like cosmic magnifying glasses. These clusters bend and amplify the light from galaxies behind them, allowing JWST to see fine details that would otherwise be invisible.
Thanks to JWST’s sharp vision, the team was able to map where stars were already present in each galaxy and where new stars were forming. A clear pattern emerged: galaxies like the Milky Way grow from the inside out. Early on, most of the stars are packed tightly into dense central regions. Over time, star formation spreads outward, building up the broad disks that later develop spiral arms.
But the most striking discovery was just how chaotic the Milky Way’s early life appears to have been. The youngest galactic twins look distorted and uneven, showing signs of frequent collisions and mergers with other galaxies. These interactions stirred up gas, triggered bursts of star formation, and gave the galaxies irregular shapes.
As time passed, these galactic look-alikes became calmer. Their structures smoothed out, collisions became rarer, and star formation settled into more stable patterns. By this stage, galaxies strongly resembled the Milky Way we know today.
The team also compared their observations with advanced computer simulations of galaxy formation. While the simulations captured the general trend of inside-out growth, they struggled to fully reproduce some details, such as how compact the earliest galaxies were and how quickly their outer regions grew. These differences give scientists valuable clues about what needs to be improved in current models.
This research highlights the power of JWST to transform our understanding of galaxy formation. As future observations push even further back in time, astronomers hope to watch Milky Way–like galaxies at their earliest, almost newborn stages.
Each new glimpse brings us closer to understanding how our own galaxy emerged from a turbulent cosmic past to become a stable home for stars, planets, and life.
Source: York University.
