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Probing Dark Energy with Clusters Animations
Click for low-resolution animation
Tour of Galaxy Clusters
Quicktime MPEG With closed-captions (at YouTube)

Since its discovery almost two decades ago, dark energy has remained one of the biggest mysteries in science. Astronomers know that dark energy is responsible for the current accelerating expansion of the Universe, but they are still trying to determine just what it is.

A new study tries to tackle the questions surrounding dark energy by examining properties of X-ray emission from galaxy clusters. Galaxy clusters are the largest structures in the Universe held together by gravity and they contain enormous amounts of hot gas that glow in X-ray light. Researchers know that galaxy clusters possess another interesting quality: the more massive ones are simply scaled up versions of the smaller ones -- like Russian dolls that fit inside one another.

Astronomers can take advantage of this fact to use galaxy clusters as cosmic distance markers. Since dark energy is pushing the Universe apart, the different distances of these galaxy clusters reveals clues about the nature of dark energy itself.

The latest research, looking at over 300 galaxy clusters, shows that dark energy does not appear to change over billions of years. This supports the idea that dark energy is what Einstein called the cosmological constant, which is the equivalent to the energy of empty space. While this new study is very exciting, there is still much to be learned before we know exactly what dark energy is, how it has affected the Universe in the past, and what it might do in the future.
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(Credit: NASA/CXC/A. Hobart)

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