🔭 Discovery of an unexpected deformation of our galaxy

2024-07-16 04:00:13

Chinese researchers have shed light on a surprising phenomenon in our galaxy: the spiral disk of the Milky Way is undergoing retrograde precession, influenced by an immense mass of dark matter forming an invisible halo. This intriguing behavior opens new perspectives on the dynamic galactic.

Artist’s interpretation of the distorted disk of the Milky Way, surrounded by a slightly flattened halo of dark matter.
Credit: Kaiyuan Hou and Zhanxun Dong (School of Design, Shanghai Jiao Tong University)

About a third of spiral galaxies exhibit a distinct warping of their disk structure. This warping, often due to past galactic collisions, can also result from interactions with satellite galaxies, the intergalactic magnetic field, and the influx of vast gas clouds. However, for the Milky Way, the main factor maintaining this warping is the halo of matter black. This deformation phenomenon is not static. It undergoes precession, that is, a change in alignment with the axis of rotation of the galaxy, similar to the movement of a spinning top. The precise measurement of this precession has long posed challenges, as previous methods relied on giant stars whose vertical movements proved imprecise.

Astronomers led by Yang Huang of the Chinese Academy of Sciences have used Cepheid variable stars as new tracers to measure this precession with unprecedented precision. Cepheids, massive, pulsating stars, provide a precise measure of their intrinsic brightness, allowing a mapping detailed deformation.

Thanks to data from the Gaia satellite of theEuropean Space AgencyHuang’s team identified a sample of 2,613 Cepheids of different ages. By grouping these stars by age range and mapping them, they were able to observe the evolution of the deformation of the galactic disk over the last 200 million years, thus discovering a precession retrograde.

The discovered precession rate is 0.12 degrees per million years, decreasing with distance from the galactic center, which could lead to increased deformation of the disk in the long term. This discovery offers clues about the flattened shape of the dark matter halo, enriching theoretical models of the formation and evolution of the Milky Way.

These results, published on June 27 in Nature Astronomycontribute to refining our understanding of dark matter and the cosmic history of our galaxy.

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