'Motion-picture' method reveals shape of the Milky Way's dark matter halo

A groundbreaking study has been conducted by an international team, who have developed a novel “motion-picture” method to measure the precession rate of the Milky Way’s disk warp. This method uses a sample of Cepheid variable stars of different ages, allowing for the clear observation of the precession direction and rate of the Milky Way’s warp.

The results of this study reveal that the current dark matter halo of the Milky Way is slightly oblate. The research paper, titled “A slightly oblate dark matter halo revealed by a retrograde precessing galactic disk warp,” was published in Nature Astronomy.

Disk galaxies, including the Milky Way, often exhibit a warped shape, a phenomenon known as a disk warp. The disk’s rotation causes it to precess due to the torque exerted by the surrounding dark matter halo. However, the measurement of this precession rate, both in direction and speed, has been a subject of debate due to the limitations of previous indirect kinematic methods.

This study utilized 2,600 classical Cepheid variable stars discovered by Gaia, along with precise distance and age data from both Gaia and LAMOST. The researchers applied the “motion-picture” method to construct the three-dimensional structure of the Milky Way’s disk across populations of various ages.

The study found that the warp precesses in a retrograde direction at a rate of 2 km/s/kpc (or 0.12 degrees per million years). Further detailed measurements showed that the precession rate decreases with radial distance, indicating that the current dark matter halo enveloping the warp is slightly oblate, with a flattening value q between 0.84 and 0.96.

This measurement offers a crucial anchor point for studying the evolution of the Milky Way’s dark matter halo. The study was published in Nature Astronomy and can be accessed with the DOI: 10.1038/s41550-024-02309-5.

The study was provided by Peking University. For more information, refer to the citation: ‘Motion-picture’ method reveals shape of the Milky Way’s dark matter halo (2024, July 1). This document is subject to copyright.

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