In this artist’s impression, the warp of the galactic disk “dances gracefully” under the torque of the dark matter halo. Credit: Hou Kaiyuan and Dong Zhanxun from School of Design, Shanghai Jiao Tong University
An international team pioneered a “moving image” method to measure the precession rate of the Milky Way’s disk deformation. Using a sample of Cepheid variable stars of different ages, this method makes it possible to clearly observe the precession direction and warp speed of the Milky Way.
Based on these measurements, the research team revealed that the Milky Way’s current dark matter halo is slightly flattened. The resulting paper, “Somewhat flattened dark matter halo revealed by retrograde precessing of the galactic warp disk”, is published in Astronomy of nature.
In the nearby Universe, nearly one-third of disk galaxies are not perfect disks, but exhibit a twisted potato chip-like shape. Astronomers refer to this phenomenon as disc deformation. The Milky Way as a typical disk galaxy also has this warp property.
Like a duck, this tilted rotating galactic disk inevitably undergoes precession due to the torque exerted by the surrounding dark matter halo. However, the measurement of this important dynamic parameter, both in direction and speed, has been highly debated.
This is because previous measurements relied on indirect kinematic methods, where the indicators used are subject to dynamic disturbances or thermal effects, which greatly limit their accuracy and precision.
This study used 2,600 classical Cepheid variable stars discovered by Gaia as tracers, along with accurate distance and age data from both Gaia and LAMOST. Using this sample, the researchers applied a “motion picture” method to construct a three-dimensional structure of the Milky Way’s disk across populations of different ages.
By “seeing” how the disc warps with age, this study found that the warp is proceeding in a 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, suggesting that the current dark matter halo surrounding the warp is slightly flattened, with a flattening value of q between 0.84 and 0.96.
This measurement provides a crucial anchor point for studying the evolution of the Milky Way’s dark matter halo.
More information:
Yang Huang et al, A slightly flattened dark matter halo revealed by a retrograde precessing galactic disc, Astronomy of nature (2024). DOI: 10.1038/s41550-024-02309-5
Provided by Peking University
Citation: Motion-picture method reveals shape of Milky Way’s dark matter halo (2024 July 1) Retrieved July 2, 2024 from https://phys.org/news/2024-07-motion-picture-method-reveals-milky .html
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