On this artist’s impression, the galactic disk warp “dances gracefully” beneath the torque of the darkish matter halo. Credit score: Hou Kaiyuan and Dong Zhanxun from the College of Design, Shanghai Jiao Tong College
A global staff has pioneered a “motion-picture” methodology for measuring the precession fee of the Milky Means’s disk warp. Utilizing a pattern of Cepheid variable stars of various ages, this methodology permits the precession route and fee of the Milky Means’s warp to be clearly noticed.
Primarily based on these measurements, the analysis staff revealed that the present darkish matter halo of the Milky Means is barely oblate. The ensuing paper, “A barely oblate darkish matter halo revealed by a retrograde precessing galactic disk warp,” is printed in Nature Astronomy.
Within the close by universe, practically one-third of disk galaxies will not be excellent disks however exhibit a warped form resembling a potato chip. Astronomers confer with this phenomenon as a disk warp. The Milky Means, as a typical disk galaxy, additionally has this warp function.
This tilted, rotating galactic disk, very like a spinning prime, inevitably undergoes precession because of the torque exerted by the encompassing darkish matter halo. Nevertheless, the measurement of this necessary dynamic parameter, each in route and fee, has been extremely debated.
It is because earlier measurements relied on oblique kinematic strategies, the place the tracers used are topic to dynamical perturbations or heating results, vastly limiting their accuracy and precision.
This research used 2,600 classical Cepheid variable stars found by Gaia as tracers, together with exact distance and age information from each Gaia and LAMOST. Utilizing this pattern, the researchers utilized the “motion-picture” methodology to assemble the three-dimensional construction of the Milky Means’s disk throughout populations of varied ages.
By “seeing” how the disk warp evolves with age, this research discovered that the warp precesses in a retrograde route at a fee of two km/s/kpc (or 0.12 levels per million years).
Additional detailed measurements present that the precession fee decreases with radial distance, indicating that the present darkish matter halo enveloping the warp is barely oblate, with a flattening worth q between 0.84 and 0.96.
This measurement offers a vital anchor level for finding out the evolution of the Milky Means’s darkish matter halo.
Extra info:
Yang Huang et al, A barely oblate darkish matter halo revealed by a retrograde precessing galactic disk warp, Nature Astronomy (2024). DOI: 10.1038/s41550-024-02309-5
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‘Movement-picture’ methodology reveals form of the Milky Means’s darkish matter halo (2024, July 1)
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