Galaxy clusters were hiding in the shadows

ACT images of cosmic background radiation, top row, with dark blue colors indicating “shadows” cast by galaxy clusters. 

Above, four optical images of the galaxy clusters, with white contour lines corresponding to the cosmic background radiation intensity levels in the ACT images.

Astrophysicists have discovered 10 new massive galaxy clusters from a large, uniform survey of the southern sky.

The survey was conducted using a breakthrough technique that detects “shadows” of galaxy clusters on the cosmic microwave background radiation, a relic of the “big bang” that gave birth to the universe.

The instrument researchers used, known as the Atacama Cosmology Telescope (ACT), collects millimeter-length radio waves that reveal images of the otherwise invisible cosmic background radiation.

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