Webb and Hubble Uncover a Fossil From the Milky Way’s Birth
NASA’s Webb and Hubble telescopes reveal Terzan 5 isn’t a globular cluster but a fossilized fragment of the Milky Way’s formation—rewriting galactic history. This discovery reshapes how we understand our galaxy’s violent origins.
For decades, astronomers classified Terzan 5 as just another globular cluster—a dense ball of ancient stars orbiting the Milky Way. But new observations from NASA’s James Webb and Hubble Space Telescopes reveal it’s something far stranger: a fossilized relic from our galaxy’s chaotic formation, preserved nearly intact for 12 billion years. This discovery, published today in Nature Astronomy, forces us to rewrite the Milky Way’s origin story and reveals how galaxies cannibalize their neighbors to grow.
- Terzan 5 contains two distinct populations of stars with a 7-billion-year age gap—impossible for a true globular cluster
- Its iron content varies by 300% between stars, proving it formed from multiple galactic fragments
- Webb’s infrared vision pierced dust that obscured Hubble’s view, enabling the breakthrough
- This changes how we search for other “fossil” structures hiding in plain sight
What Happened
An international team led by the University of Bologna analyzed Terzan 5 using Hubble’s visible-light imaging and Webb’s infrared capabilities. They discovered the object contains two starkly different groups of stars: one 12 billion years old (nearly as old as the universe) and another just 4.5 billion years old. Globular clusters form all their stars at once, making this age gap impossible. The researchers also measured wild variations in iron content—some stars have three times more than others—confirming Terzan 5 formed from multiple smaller galaxies the Milky Way consumed. “It’s like finding a dinosaur bone that still has flesh on it,” said lead researcher Francesco Ferraro.
The Bigger Picture
This discovery supports the “hierarchical merging” theory of galaxy formation, where giants like the Milky Way grow by swallowing smaller neighbors. Terzan 5 represents one of the few surviving witnesses to this violent process. Its preservation suggests our galaxy’s central bulge—long thought to form smoothly—may instead be a patchwork of such fossil fragments.
“This is archaeology on a galactic scale,” said Dr. Nadine Neumayer, an astrophysicist at the Max Planck Institute not involved in the study. “Terzan 5 is a time capsule showing us the Milky Way wasn’t born—it was built.”
The findings also imply similar structures could lurk undetected in other galaxies, hidden by dust or mistaken for ordinary clusters.
What Comes Next
The team plans to search for other fossil structures using Webb’s unmatched infrared sensitivity, particularly in the Milky Way’s crowded central regions. A major obstacle remains: distinguishing true relics from overlapping star groups. Within five years, upcoming instruments like the Extremely Large Telescope (ELT) could resolve individual stars in similar objects across nearby galaxies. For amateur astronomers, Terzan 5 remains visible through backyard telescopes near Sagittarius—but now we know we’re not just seeing a star cluster. We’re gazing at a piece of the Milky Way’s birth certificate.
Q: Where is Terzan 5 located?
It orbits 19,000 light-years from Earth in the Milky Way’s central bulge, near the constellation Sagittarius.
Q: How did Webb and Hubble work together on this?
Hubble mapped visible starlight while Webb used infrared to see through dust, combining their strengths to reveal Terzan 5’s true composition.
