In this artist’s impression, the deformation of the galactic disk “dances gracefully” under the rotational momentum of the dark matter halo. Credit: Hou Kaiyuan and Dong Zhanxun from School of Design, Shanghai Jiao Tong University
An international team has created a “motion-picture” method for measuring the precession rate of the Milky Way’s disk distortion. Using a sample of Cepheid variable stars of different ages, this method allows the direction of precession and the rate of distortion of the Milky Way to be clearly observed.
Based on these measurements, the research team found that the Milky Way’s current dark matter halo is slightly faint. The resulting paper, “A faintly decayed dark matter halo revealed by a retrograde-preceding galactic disc distortion,” is published in Astronomy of Nature.
In the nearby universe, nearly a third of disk galaxies are not perfect disks, but exhibit a deformed shape resembling a potato chip. Astronomers refer to this phenomenon as a disk deformation. The Milky Way, as a typical disk galaxy, also has this warping feature.
This tilted, rotating galactic disk, much like a spinning top, 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 much debated.
This is because previous measurements relied on indirect kinematic methods, where the trackers used are subject to dynamic disturbances or heating effects, greatly limiting their accuracy and precision.
This study used 2600 classical Cepheid variable stars discovered by Gaia as tracers, together with accurate distance and age data from Gaia and LAMOST. Using this sample, the researchers applied the “photo-motion” method to construct the three-dimensional structure of the Milky Way’s disk across populations of different ages.
By “watching” how the disk’s distortion evolves with age, this study found that the deformation proceeds in a retrograde direction at a rate of 2 km/s/kpc (or 0.12 degrees per million years).
Further detailed measurements show that the precession rate decreases with radial distance, indicating that the actual dark matter halo surrounding the warp is slightly stretched, with a flattening q value between 0.84 and 0.96.
This measurement provides a key point for studying the evolution of the Milky Way’s dark matter halo.
More information:
Yang Huang et al, A slightly extended dark matter halo revealed by a distortion of the retrograde progenitor 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 3, 2024 from https://phys.org/news/2024-07-motion-picture- method-reveals-milky .html
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