Chinese astronomers have made a new discovery, showing that the warping in the Milky Way's spiral disk is in retrogression, that is, it changes position over time under the influence of the mass of the object. Huge dark matter surrounds the galaxy.
About a third of all spiral galaxies have a distinctly warped disk-shaped structure, like a bent music record. The cause of this phenomenon could be due to a collision with another galaxy in the past, but could also be due to interactions with satellite galaxies, intergalactic magnetic fields, or the infall of stars. giant gas cloud. However, in the case of the Milky Way, the main agent that causes and maintains this warping is the halo of dark matter that surrounds the disk and exerts torque on it.
The warping of the Milky Way is not a fixed phenomenon but it is precessing, that is, changing position over time relative to the galaxy's rotation axis. This is similar to the phenomenon of a spinning top wobbling when spinning.
However, measuring this precession rate has proven to be a major challenge. Previous estimates relied on the vertical motion of giant stars to calculate this speed but were inaccurate, leading to results that contradicted theory.
A team of astronomers led by Yang Huang of the Chinese Academy of Sciences used a new tool to precisely measure warp precession rates using Cepheid variable stars.
These stars have an oscillation period related to their intrinsic brightness, which helps to accurately calculate their distance from us. This makes them excellent tracers for warp mapping.
Using data from the European Space Agency's Gaia astronomy spacecraft, Huang's team identified a sample of 2,613 Cepheid variable stars of various ages.
By grouping Cepheids by age and mapping them, the team was able to show the shape and location of the warp at different times over the past 200 million years. As a result, they discovered that the warp was precessing upstream, at a speed of 2km per second per kiloparsec.
Furthermore, the motion picture shows that the precession rate decreases with distance from the galactic center, which would lead to greater curvature of the disk over time. Models indicate that this decrease is due to the dark matter halo creating a flattened shaped torque.
The shape of the dark matter halo is important because it provides data that helps theorists build models to predict what dark matter is made of. It also offers clues about the history of the Milky Way's formation and how it evolved through collisions and interactions with smaller galaxies and other gas clouds.
