2024-07-02 16:13:15
An international team has developed a “moving picture” method to measure the precession rate of disk deformation. The Milky Way.
Using a sample of Cepheid variable stars of different ages, this method allows us to clearly observe the direction of precession and the rate of deformation of the star. The Milky Wayaccording to the authors.
Based on these measurements, the Peking University research team revealed that the halo of dark matter stream, the invisible mass surrounding our galaxy, of The Milky Way It is slightly flattened. He resulting article is published in Nature Astronomy.
In the nearby universe, nearly a third of disc galaxies are not perfect discs, but have a warped shape similar to a potato chip. Astronomers refer to this phenomenon as disc warping. The The Milky Wayas a typical disk galaxy, also has this warping feature.
This tilted and rotating galactic disk, very much like a peak, undergoes inevitable precession due to the torque exerted by the halo of dark matter which surrounds it. However, the measurement of this important dynamic parameter, both in direction and speed, has been highly debated.
This is because previous measurements were based on indirect kinematic methods, where the tracers used are subject to dynamic disturbances or heat effects, which greatly limits their precision and accuracy.
Three-dimensional structure of the plate The Milky Way
This study used 2,600 classical Cepheid variable stars detected by Gaia as tracers, along with accurate distance and age data from both Gaia and LAMOST. Using this sample, the researchers used the “moving image” method to construct the three-dimensional structure of the disk of The Milky Way across populations of different ages.
By “watching” how disc deformation evolves with age, this study found that deformation continues in the retrograde direction at a rate of 2 km/s/kpc (or 0.12 degrees per million years).
More detailed measurements show that the precession rate decreases with radial distance, indicating that the halo of dark matter the flow surrounding the curvature is slightly flattened, with a flattening value q between 0.84 and 0.96.
Given the young nature of the disk deformation traced by the Cepheids (less than 200 Myr), the focus of this research is directly measuring the shape of the Cepheid halo. dark matter actual.
This measurement provides a crucial anchor point for studying the evolution of the halo dark matter of The Milky Way.
(With information from Europa Press)
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