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