Discovery of RR Lyrae Stars in the Nuclear Bulge of the Milky Way
  Galactic nuclei, like the one of the Milky Way, are extreme places with high
stellar densities and, in most cases, hosting a supermassive black hole. One of
the scenarios proposed for the formation of the Galactic nucleus is by merging
of primordial globular clusters (Capuzzo-Dolcetta 1993). An implication of this
model is that this region should host stars characteristically found in old
Milky Way globular clusters. RR Lyrae stars are primary distance indicators,
well known representatives of old and metal-poor stellar populations, and
therefore regularly found in globular clusters. Here we report the discovery of
a dozen RR Lyrae ab-type stars in the vicinity of the Galactic center, i.e. in
the so-called nuclear stellar bulge of the Milky Way. This discovery provides
the first direct observational evidence that the Galactic nuclear stellar bulge
contains ancient stars (>10 Gyr old). Based on this we conclude that merging
globular clusters likely contributed to building-up the high stellar density in
the nuclear stellar bulge of the Milky Way.
