After getting a clearer view of the center of the Milky Way, researchers discovered a dozen ancient stars of the RR Lyrae variety, shedding insight on how the galaxy's bulging core came to be.
In a paper published in The Astrophysical Journal Letters, the researchers detailed how using the VISTA infrared survey telescope to observe the Milky Way's center, as part of the Variables in the Via Lactea ESO public survey, gave them a clearer look at the region by cutting through cosmic dust.
RR Lyrae stars are usually located in dense globular clusters. Variable stars, they have brightness levels that regularly fluctuate. By observing how long periods of dimming and brightening last in an RR Lyrae, it was possible to calculate its distance from the center of the galaxy.
Unfortunately, RR Lyraes are commonly outshone by younger, brighter stars, with some further obscured by cosmic dust. This is where the VISTA telescope helped. But even with the aid of an infrared telescope, the researchers said looking for RR Lyrae stars in the middle of the crowded center of the Milky Way was daunting.
Like other galaxies, the Milky Way features a densely populated core. Fortunately, unlike other galaxies, it is close enough that it can be studied at depth. And with the discovery of the stars RR Lyrae, the researchers gained compelling evidence that would help researchers in deciding between two theories explaining how the Milky Way's center formed.
With the presence of a dozen RR Lyrae stars confirmed, the researchers' discovery indicates that ancient globular cluster remains are scattered within the Milky Way's bulging core.
"The evidence supports the scenario in which the bulge was originally made out of a few globular clusters that merged," said Rodrigo Cotreras Ramos, one of the study authors.
The other theory hypothesized that the Milky Way's bulging core was formed because of rapid gas accretion. As RR Lyrae stars are almost always found in globular clusters, it's more sound to conclude that the center of the galaxy was formed when these clusters merged. By extension, this would also mean that other bulging cores were formed in the same manner.
Aside from supporting an important galactic evolution theory, RR Lyrae stars are highly likely to be more than 10 billion years old, making them possibly survivors of potentially the oldest, most massive cluster of stars residing within the Milky Way.
Earlier in September, a study published in the journal Science Advances mapped the Milky Way and discovered that the galaxy is not spiral in form, with clear-cut, distinct arms. Rather, the Milky Way is made up of different branches and many subtle spurs.
