A new class of fossil fragments from the hierarchical assembly of the Galactic bulge

TL;DR

This paper presents evidence that certain globular cluster-like systems in the Galactic bulge, specifically Liller 1 and Terzan 5, contain multiple stellar populations of different ages, supporting the hierarchical assembly model of the Milky Way's bulge.

Contribution

It identifies multiple stellar populations in Liller 1, demonstrating recent star formation and supporting hierarchical bulge formation theories.

Findings

Liller 1 hosts two distinct stellar populations with ages 1-3 Gyr and 12 Gyr.

Both Liller 1 and Terzan 5 show evidence of recent star formation in the bulge.

Supports hierarchical assembly of the Galactic bulge through primordial structures.

Abstract

The formation and evolutionary processes of galaxy bulges are still unclear, and the presence of young stars in the bulge of the Milky Way is largely debated. We recently demonstrated that Terzan 5, in the Galactic bulge, is a complex stellar system hosting stars with very different ages and a striking chemical similarity to the field population. This indicates that its progenitor was likely one of the giant structures that are thought to generate bulges through coalescence. Here we show that another globular cluster-like system in the bulge (Liller 1) hosts two distinct stellar populations with remarkably different ages: only 1-3 Gyr for the youngest, 12 Gyr for the oldest, which is impressively similar to the old component of Terzan 5. This discovery classifies Liller 1 and Terzan 5 as sites of recent star formation in the Galactic bulge and provides clear observational proof that the hierarchical assembly of primordial massive structures contributed to the formation of the Milky Way spheroid.