With the help of the European Southern Observatory's infrared VISTA telescope, astronomers have discovered a cluster of ancient stars at the center of the Milky Way. It's the first time RR Lyrae have been found in the Milk Way.

RR Lyrae stars are variable stars mostly exclusive to stellar populations at least 10 billion years old. Their discovery at the heart the Milky Way suggests the galaxy was formed by the coming together of primordial star clusters.

Because most galactic centers are densely populated, they're difficult to study. Fortunately for astronomers, the Milky Way's center is close enough to survey in depth.

Still, RR Lyrae stars are often obscured by the light of younger, brighter stars and clouds of dust. Their discovery was only recently made possible by the infrared analysis employed by VISTA as part of ESO's Variables in the Via Lactea survey.

Scientists hope the discovery of a dozen RR Lyrae stars in the crowded Milky Way center will help astronomers model the formation of galactic bulges -- the ancient dense cores found at the middle of most spiral galaxies.

"This discovery of RR Lyrae Stars in the center of the Milky Way has important implications for the formation of galactic nuclei," Rodrigo Contreras Ramos, an astronomer at the University of Chile, said in a news release. "The evidence supports the scenario in which the nuclear bulge was originally made out of a few globular clusters that merged."

While some astronomers believe galactic bulges are the result of globular cluster mergers, others argue they are caused by the accretion of gas. The discovery of RR Lyrae stars, typically only found in clusters, lend credence to the mergers theory.

Researchers detailed their discovery in the Astrophysical Journal.