Turns out that the ancient star system Terzan 5 is not a globular star cluster, a classification that typically has only one ancient star population. New data not only confirms the existence of two distinct populations of stars in Terzan 5, but also provides evidence for two more recent rounds of star formation.
As a result, researchers have reclassified Terzan 5 as a bulge fossil fragment or BFF. These findings were made possible by data from two of our most powerful observatories—the James Webb and Hubble space telescopes.
Although this system is located within the crowded bulge of our Milky Way galaxy and began forming its first stars 12 billion years ago, Terzan 5 was massive enough to maintain its separate identity—while other, lighter-weight star systems spread out and mixed to form the bulge, or core of our galaxy, billions of years ago. Terzan 5 is like a lump in an otherwise well-mixed cake batter.
Terzan 5’s first generation of stars formed roughly 12 billion years ago—as the Milky Way itself was assembling—and another about 4.7 billion years ago, just before the Earth started forming. The third generation formed 3.8 billion years ago and the fourth only 2.5 billion years ago.
Credit: Image: NASA, ESA, STScI, Giorgia Zullo (University of Bologna), Francesco R. Ferraro (University of Bologna); Image Processing: Alyssa Pagan (STScI).
