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 probably 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, and 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.

星系凸起的形成和演化过程仍不清楚，银河系凸起中是否存在年轻恒星引起了很大争议。我们最近证明，银河系凸起处的Terzan 5是一个复杂的恒星系统，该恒星系统容纳了不同年龄的恒星，并且与野外种群具有惊人的化学相似性。这表明其祖先可能是被认为通过聚结产生凸起的巨型结构之一。在这里，我们显示了凸起中的另一个球状星团状系统（Liller 1）拥有两个明显不同年龄的不同恒星种群：最年轻的只有1–3 Gyr，最老的只有12 Gyr，这与旧的相似Terzan的组件5。