This Hubble image from 2002 shows dark matter in the galaxy cluster Abell 1689. The cluster, 2.2 billion lightyears from Earth, contains about 1,000 galaxies and trillions of stars. Hubble cannot see dark matter directly. Astronomers inferred its location by analyzing the effect of gravitational lensing. The densest concentration of dark matter (seen as a blue tint) is in the cluster's core.
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