This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The cosmic microwave background (CMB) is a faint glow in the universe dating back to roughly 380,000 years after the Big Bang, long before stars or galaxies emerged. Detecting this light and mapping its fluctuations provide valuable insights into the age and composition of the universe.
Researchers at Columbia University recently analyzed CMB data and gathered evidence of a CMB signal that could be produced by internal gas motions in galaxy clusters, large collections of galaxies that are held together by gravity. Their findings, published in Physical Review Letters, strengthen earlier clues of this gas motion and a phenomenon called the rotational kinematic Sunyaev-Zel'dovich (rkSZ) effect reported by other astronomers. "This project began after a meeting with my Ph.D. adviser, J.
Colin Hill, in which we discussed signals in the CMB that hadn't yet been observed," Samuel Goldstein, first author of the paper, told Phys.org. "One of these is the rkSZ effect. As CMB photons pass through a galaxy cluster, they scatter off its ionized gas, and if the gas is rotating, one side of the cluster appears slightly hotter and the other slightly colder." Goldstein and Hill's study drew inspiration from earlier work by Eric Baxter and collaborators at the University of Pennsylvania and other institutions.
This previous study offered initial hints of the rkSZ signal in galaxy clusters. "We built on their work by analyzing a larger sample of clusters and developing several new data-analysis techniques to improve our sensitivity to the rkSZ effect," said Goldstein. Gas moving inside galaxy clusters would leave several subtle imprints on the CMB.
For instance, theoretical predictions suggest that it would slightly change the radiation, producing a temperature shift. "Due to the Doppler effect, gas moving toward us makes the CMB appear slightly hotter, while gas moving away makes it slightly colder," explained Goldstein. "As a result, a cluster whose rotation axis lies perpendicular to our line of sight will appear slightly hotter on the side approaching us and slightly colder on the side receding, producing a dipole pattern across the cluster." The signal resulting from the flow of gas is typically too faint to be detectable in a single galaxy cluster.
Goldstein and Hill therefore aligned and averaged CMB observations collected from 25 different clusters that displayed signs of internal motion, such as cluster rotation and mergers. Each of the 25 clusters they examined was made up of at least 50 member galaxies that were recorded by the Sloan Digital Sky Survey (SDSS). The SDSS is a large astronomical survey aimed at mapping the sky, capturing images and light spectra of stars, galaxies and other objects in the universe.
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