Researchers using two of humanity’s most powerful observatories — NASA’s James Webb and Hubble Space Telescopes — have definitively shown that Terzan 5 is not a globular star cluster as it was once classified. The finding challenges long-held assumptions about this stellar grouping and offers new insight into how galaxies like our own form and evolve over time.
Terzan 5 has long been considered a globular cluster, a densely packed ball of ancient stars. The combined observations from Webb and Hubble revealed that it possesses a mix of stellar populations with different ages and chemical compositions, a trait inconsistent with typical globular clusters, which contain stars of similar age and composition.
The study relied on Webb’s infrared capabilities to peer through dust and Hubble’s sharp visible-light imaging to dissect the cluster’s stellar populations. This multi-wavelength approach allowed researchers to identify distinct bursts of star formation within Terzan 5, indicating a more complex history.
These findings recalibrate our understanding of the Milky Way’s assembly, suggesting that Terzan 5 may be a relic from the galaxy’s formation, possibly the core of a dwarf galaxy that merged with the Milky Way. Future observations aim to uncover similar relics to map the galaxy’s evolutionary timeline.
While the evidence is strong, some astronomers caution that Terzan 5 could be an extreme example of a globular cluster rather than a new class of object. The classification debate underscores the need for further spectroscopic analysis to confirm its origin.