The invisible universe: how dark matter shapes the cosmos

Space · Published 16 October 2026 Swipe more like this →

In short: While most galaxies glow across the cosmos, a rare class of objects remains nearly invisible to our instruments. These low-surface-brightness systems are dominated by dark matter and contain only sparse, faint stars. Recent discoveries like CDG-2 are challenging our current models of how the universe evolved and organized itself.

Astronomers have identified a mysterious class of low-surface-brightness galaxies that are dominated by dark matter. One such example, CDG-2, is located in the Perseus galaxy cluster approximately 300 million light-years away. Unlike typical galaxies, CDG-2 contains only a sparse scattering of faint stars, making it extraordinarily difficult to detect using standard methods.

The discovery of CDG-2 was made by David Li and his team at the University of Toronto. To locate dense, spherical star groups known as globular clusters, the researchers applied sophisticated statistical methods. This discovery proved significant as CDG-2 represented the initial galaxy identified purely via its globular cluster population. Follow-up observations using NASA’s Hubble Space Telescope, ESA’s Euclid space observatory, and the ground-based Subaru Telescope confirmed a faint, diffuse glow surrounding four specific clusters.

The composition of CDG-2 challenges our understanding of galactic evolution. Initial data indicates its brightness equals approximately 6 million Sun-like stars, while 16% of its visible matter consists of globular clusters. Incredibly, dark matter—a substance that neither emits, absorbs, nor reflects light—makes up 99% of its total mass. Gravitational pulls from neighboring galaxies within the cluster probably removed a large portion of the hydrogen gas needed to create stars.

Similar mysteries arise in the early universe. The James Webb Space Telescope recently identified XLSSC 122, a galaxy cluster located 10.4 billion light-years away. Dating back to "cosmic noon," this cluster is unexpectedly mature, displaying organized structures typically seen in the modern universe. The presence of a dense dark matter concentration also implies that certain cosmic structures might have formed more rapidly than existing theories suggest. Scientists use the cluster's strong gravitational lensing to measure this invisible mass with exceptional precision.

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