Four Stellar Generations Prove Terzan 5 Is Fossil of Milky Way, Not Cluster
Astronomers have reclassified Terzan 5 from a globular cluster to a 'bulge fossil fragment' after discovering four distinct stellar generations. This finding, made using the James Webb and Hubble telescopes, provides new insights into the formation of the Milky Way's central bulge.
Why it matters
This discovery challenges long-held astronomical classifications and offers a new method for mapping the hierarchical formation of galaxies.
For 58 years, astronomers cataloged Terzan 5 as a globular cluster - one of the ancient, densely packed balls of stars orbiting the Milky Way's central bulge. A peer-reviewed study published June 16, 2026, in Astronomy & Astrophysics has definitively ended that classification. Using the combined power of the James Webb Space Telescope and the Hubble Space Telescope, a team led by PhD student Giorgia Zullo at the University of Bologna has confirmed that Terzan 5 contains not one but four distinct stellar generations spanning 10 billion years - evidence that rules out every globular-cluster explanation and establishes the system as the prototype of an entirely new class of cosmic object: the bulge fossil fragment.
The article is a straightforward report on scientific findings published in a peer-reviewed journal.
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