Astronomers have identified a region near the center of the Milky Way that remains remarkably stable despite its proximity to the galaxy’s violent core. Research published by the Monthly Notices of the Royal Astronomical Society indicates that a specific population of stars—known as RR Lyrae variables—provides a “calm” window into the history of the galactic bulge, showing little evidence of the intense gravitational disruption expected in such a dense environment.
Why the galactic center is typically considered violent
The center of the Milky Way is dominated by a supermassive black hole, Sagittarius A*, and a dense, high-velocity collection of stars and gas. According to NASA, the gravitational forces in this region are extreme, leading to frequent stellar collisions, tidal disruptions, and the rapid formation of new stars. Because of this chaos, scientists have historically struggled to map the oldest structures in the galactic bulge. The region is often obscured by thick clouds of interstellar dust, which block visible light and complicate efforts to track the movement and age of individual stellar populations.
How RR Lyrae stars reveal a different story
To study this region, researchers led by Dante Minniti of the Universidad Andrés Bello utilized data from the VISTA Variables in the Via Lactea (VVV) survey. RR Lyrae stars are ancient, pulsating variables that act as “standard candles,” meaning their intrinsic brightness is well-understood, allowing astronomers to calculate their exact distances from Earth.
The study found that these ancient stars are distributed in a way that suggests the inner bulge formed slowly and steadily rather than through a single, violent event. Unlike younger stars that show signs of being pulled and stretched by the black hole’s gravity, these RR Lyrae stars maintain a relatively stable, spherical distribution. This suggests they belong to an older “fossil” population that predates the more recent, chaotic building phases of the galaxy.
What this means for galactic evolution
The discovery of this stable population challenges existing models of how galaxies grow. By comparing the distribution of these ancient stars to younger populations, the researchers established a timeline for the Milky Way’s development.
While younger stars in the bulge show a “bar-like” structure caused by the galaxy’s rotation and gravitational interactions, the RR Lyrae stars remain largely unaffected by these forces. This contrast indicates that the inner galaxy is composed of layers: a newer, dynamic structure built on top of a much older, more tranquil foundation. This finding provides a clearer picture of how the Milky Way assembled its mass over the last 10 to 12 billion years.
Key Takeaways
- Ancient Stability: RR Lyrae stars act as ancient markers that show the inner Milky Way has a stable, older core.
- Survey Methodology: The VVV survey provided the infrared data necessary to see through the dust of the galactic plane.
- Structural Layers: The galaxy appears to be a composite, with a calm, ancient population distinct from the more chaotic, younger stars in the bulge.
- Standard Candles: Because RR Lyrae stars have a predictable light pattern, they remain the most reliable tools for mapping the distance and age of the deep galactic interior.
Future observations from the James Webb Space Telescope are expected to build on this research by providing even higher-resolution imagery of these ancient stars, potentially uncovering more “calm” pockets in the heart of the galaxy that were previously hidden from view.
Worth a look