A prominent area of research in modern astrophysics is the enigmatic dark matter phenomenon. The groundbreaking work of Vera Rubin in the 1970s revealed that the outer edges of galaxies rotate at unexpected speeds, contrary to predictions based solely on visible matter. This led researchers to investigate and classify these observations under the term dark matter. Numerous studies have documented how light bends around galaxy clusters and the distribution of matter in the universe, as well as fluctuations in cosmic microwave background radiation, all indicating that the universe holds more secrets than what astronomers can visibly observe.
According to widely accepted cosmological models, the ΛCDM model describes dark matter as a type of slow-moving particle that possesses mass and exerts gravitational force but does not interact with electromagnetic radiation. As a result, dark matter remains invisible and can seamlessly pass through ordinary matter.
The quest to identify dark matter particles is an ongoing effort, allowing scientists to investigate their characteristics, including their distribution throughout the Milky Way. Although scientists can calculate the movement of stars from the galaxy’s center to the Sun without factoring in dark matter, the presence of this invisible mass significantly influences stars and gas clouds found further out. Researchers suggest that the dark matter halo encircles the galaxy, extending up to 230,000 parsecs (approximately 4 quintillion miles or 7 quintillion kilometers) from the galactic center, and may account for roughly 95% of the Milky Way’s total mass.
A research team from University College London has been examining the geometry of the Milky Way’s dark matter halo. They hypothesized that the Milky Way is in a state of equilibrium and analyzed the stable positions of stars in the galaxy’s outer regions to model the shape and orientation of the dark matter halo that permits their presence. Their findings were then correlated with previous studies of the Milky Way’s evolution, providing a more comprehensive understanding of the galaxy’s structure.
This research leveraged data from the Gaia survey, a satellite mission that observed millions of stars and mapped the Milky Way galaxy from 2013 to 2025. The team utilized two primary types of data: the average number of stars within specific volumes in the outer regions of the galaxy’s old structures and the stars’ positions and velocities within the stellar halo. The team discovered that the stellar halo is elliptical and tilted concerning the Milky Way, primarily due to a similarly-shaped but significantly larger dark matter halo.
A simplified diagram illustrating the shape and orientation of the dark matter halo compared to the stellar halo and the Milky Way’s disk. Not to scale. By the author.
The research team concluded that their findings dismiss the earlier notion that the dark matter halo is approximately spherical. They determined that the halo’s tilt, relative to the Milky Way’s disk, is around 43 degrees. This tilt mirrors other disk galaxies with dark matter halos, which typically range between 46.5° and 18° with regards to their stellar halos. The researchers contended that a stable, tilted, non-spherical dark matter halo signifies the overall stability of the galaxy, especially in light of past galactic collisions that occurred at least 8 billion years ago. Enhanced measurements of the halo’s shape could provide valuable insight into these markedly significant merge events.
To facilitate future research, the team generated a model that accurately reflects a snapshot of a galaxy with a tilted, rectangular dark matter halo. This model incorporates the stars’ density and motion patterns that they examined. Additional refinements in their simulations are consistent with findings from the Gaia survey, revealing that the halo becomes increasingly tilted moving away from the galactic center. Specifically, the tilt escalates from 10 degrees to 35 degrees at distances between 6 and 60 kiloparsecs (approximately 100 to 100 quintillion miles or 200 to 2 quintillion kilometers), while also transitioning from being elliptical to more circular as the distance increases. They propose that future researchers explore this model further, incorporating other complex interactions, such as those with the Large Magellanic Cloud.
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Source: sciworthy.com
