A fossil of the Milky Way, hiding in plain sight among the stars

Terzan 5 looks like an ordinary globular cluster — a dense swarm of stars. Look closer, with the infrared eyes of the James Webb Space Telescope and 12 years of Hubble observations, and it falls apart into something stranger: four distinct generations of stars, the remains of a much larger system that survived as the Milky Way's central bulge grew around it. Astronomers led by Giorgia Zullo at the University of Bologna identify Terzan 5 as a 'bulge fossil fragment' — a surviving piece of the galaxy's construction site, published in Astronomy & Astrophysics. It is, in effect, a fossil you can see in a telescope: a chunk of the young Milky Way, preserved.