X-ray Distance Measurement Technique
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This series of stills shows the technique used to make distance
measurements to galaxy clusters. Chandra's observations are used to
determine the ratio of the mass of the hot gas and the mass of the dark
matter in different galaxy clusters. This "gas fraction" depends on the
assumed distances to the clusters, which in turn depends on the amount of
matter and dark energy in the Universe. Because galaxy clusters are
extremely large, the gas fraction should be the same for every cluster, and
so the distances to the clusters are adjusted to satisfy this
requirement. Each of the 3 illustrations shows Chandra in the top left,
observing a galaxy cluster, shown in the top right (in red). The relative
amounts of hot gas (in red) and dark matter (in blue) are shown at the
bottom, with the green marker giving the expected, correct amount. The
first illustration shows a gas fraction that is too small, implying that
the distance to the cluster is too small, the second shows the correct gas
fraction and distance, and the third illustration shows a gas fraction and
distance that are too large.
[Run Time: 0:12]
Credit: NASA/CXC/M. Weiss
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