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Terzan 5 Redefined as Bulge Fossil After Four Generations

6/18/2026

Summary

Astronomers Reclassify Terzan 5

Astronomers in the United States reclassified Terzan 5 as a “bulge fossil fragment” after identifying four distinct stellar generations.
Hubble Space Telescope and James Webb Space Telescope observations revealed the four star populations.
Researchers reported the findings in Astronomy & Astrophysics, presented them at the American Astronomical Society conference in Pasadena, California, on June 16 2026, and noted earlier studies had found only two generations.

Summary

Astronomers Confirm

Keck, the Very Large Telescope and other observatories confirmed Terzan 5’s multi-generational stars, linking it to early-universe bulge formation.
Astronomer Azop Terzan first identified the cluster in 1968, providing a historical anchor.
Associate professor Barbara Lanzoni said simulations show primordial gas disks fragmenting into clumps that merge inward, with Terzan 5 as evidence.
The team combined Hubble, James Webb, Keck and VLT data and highlighted the upcoming September launch of NASA’s Nancy Grace Roman Space Telescope.

Summary

Astronomers Map Terzan 5

Astronomers used a 12-year Hubble baseline to measure motions and separate Terzan 5 members from foreground stars.
Pairing Webb’s infrared with Hubble data let them catalog more faint stars than any prior study.
Spectroscopy from Keck Observatory and ESO’s Very Large Telescope confirmed distinct chemical signatures among four populations.
Co-author R. Michael Rich said supernova-driven enrichment stayed because the progenitor’s mass prevented gas loss, showing multi-epoch, multi-wavelength data can reveal stellar histories.

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Astronomers Reclassify Terzan 5

Astronomers in the United States reclassified Terzan 5 as a “bulge fossil fragment” after identifying four distinct stellar generations.
Hubble Space Telescope and James Webb Space Telescope observations revealed the four star populations.
Researchers reported the findings in Astronomy & Astrophysics, presented them at the American Astronomical Society conference in Pasadena, California, on June 16 2026, and noted earlier studies had found only two generations.

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