In a recent study, researchers have revealed that stars at the fringes of our Milky Way move slower than expected, suggesting a new understanding of dark matter in our galaxy. This discovery challenges the current models of dark matter distribution and could pave the way for new theories on galaxy formation.
Position of our Sun in the Milky Way.
Image NASA
Astronomers have long used galaxy rotation curves to study the presence of dark matter. These curves depict the orbital speed of stars relative to their distance from the galactic center. According to current theories, dark matter, invisible yet detectable through its gravitational influence, should maintain a constant velocity of stars, even those far from the center.
However, a team led by Anna-Christina Eilers from the Massachusetts Institute of Technology (MIT) utilized data from the European Space Agency's Gaia mission to analyze the orbital speeds of stars up to 80,000 light-years from the galactic center. The results showed a nearly flat rotation curve, with only a slight decrease in speed for the outermost stars.
Additional observations, combining Gaia data with that from the APOGEE (Apache Point Observatory Galactic Evolution Experiment), extended this analysis up to about 100,000 light-years. Lina Necib, an assistant professor of physics at MIT, found that the curve remained flat up to a certain distance, then dropped sharply. This indicates that the outer stars rotate slower than expected.
This decrease suggests there's less dark matter at the center of our galaxy than previously thought. The research team describes the galaxy's dark matter halo as "hollowed out," akin to a cored apple. Moreover, the gravity produced by the existing dark matter does not seem sufficient to keep stars moving at these extreme distances.
This discovery raises questions about the consistency of our current measurements and stimulates excitement in the scientific community to solve this mystery. Researchers plan to use high-resolution computer simulations to model different dark matter distributions in our galaxy and see which distribution best replicates the observed rotation curve. These models could help explain how the Milky Way acquired its specific dark matter distribution and why other galaxies did not.
The results of this study were published on January 8 in the journal
Monthly Notices of the Royal Astronomical Society.