Credit: Image: NASA, ESA, STScI, Giorgia Zullo (University of Bologna), Francesco R. Ferraro (University of Bologna); Image Processing: Alyssa Pagan (STScI)

Terzan 5 is a stellar system orbiting within the Milky Way galaxy’s bulge, which is an incredibly bright, crowded central region of the galaxy. Not only are stars within the bulge tightly packed together — every bit of this region is laced with thick clouds of gas and dust.

NASA’s James Webb and Hubble Space Telescopes joined forces to study Terzan 5. Astronomers already knew that this star cluster was unusual in that it contained two stellar populations of very different ages – one that formed about 12 billion years ago and one that formed 5 billion years ago. New research found strong evidence for two more stellar populations, one that formed 3.8 billion years ago and another only 2.5 billion years ago. The research team also was able to determine the ages of the previously known stellar populations with unprecedented precision, finding that they formed 12.5 billion and 4.7 billion years ago.

This finding proved that Terzan 5 is not a globular star cluster, as originally classified. Instead, Terzan 5 belongs to a new category, known as a bulge fossil fragment — a self-contained, self-enriching stellar system with multiple star populations of different ages and with different iron abundances.

Terzan 5 is 22,000 light-years away in the constellation Sagittarius.

Provider: Space Telescope Science Institute

Image Source: /image/stsci/2026-123a

Curator: STScI

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