Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester.
An artist's impression of the warped disk of the Milky Way, surrounded by a slightly flattened dark matter halo.The warp in the Milky Way's spiral disk is precessing backward under the influence of the enormous mass of dark matter that forms an invisible halo around our galaxy, Chinese astronomers have discovered.have a distinct warp to their disk-shaped structure, like a vinyl record that has been bent.
Measuring the warp's rate of precession, however, has proven challenging in the past. Previous estimates have attempted to use the vertical motion of bright, but old, giantas tracers to calculate the rate of precession. However, such tracers are notoriously imprecise, and results based on them had suggested — counter to theory — that the disk is precessing prograde and not retrograde , as had been expected.
"Age is key to measuring the precession rate of the disk warp," say the authors in their research paper."We obtained a motion picture of the disk warp by mapping the three-dimensional distributions for Cepheid samples of different ages." Each Cepheid retains information on its position in the warp when it was born, so by grouping the Cepheids into different age ranges and mapping them, Huang's team were able to show the shape and position of the warp at different points inover the past 200 million years. By then running the individual maps together, like a motion picture, they were able to see the warp precessing.
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