Galaxy clusters reveal dark matter through how their galaxies move.

Galaxy clusters are huge groups of galaxies. Scientists want to use them to study fundamental physics, including cosmic structure, dark matter, dark energy, and gravity. To do this, researchers must map out how mass is spread inside each cluster. Getting this mass profile right has been a hard, ongoing challenge. In this review, researchers look at cluster kinematicskinematicsThe study of motion, here referring to how galaxies move within a cluster., which means tracking how member galaxies move within a cluster. Gravity pulls on these galaxies, so their speeds and paths reveal where hidden mass is located. Large collections of light data, called spectroscopic datasets, now allow scientists to use advanced models to measure these cluster masses and study their internal dynamics. The authors found that tracking galaxy motions competes well with other methods. It helps scientists map out mass, test cosmological models, place limits on dark matter and dark energy, and inspect how gravity works across millions of parsecs.

Why it matters

Galaxy clusters are the largest structures in the universe, and their mass tells us about dark matter, dark energy, and gravity. By studying how galaxies move within clusters, astronomers can map this invisible mass and test our understanding of the cosmos. This work helps refine cosmological models and could lead to new insights about fundamental physics.

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