Galaxy clusters used to measure dark energy

Galaxy clusters could be used as markers to investigate dark energy, the invisible and mysterious energy causing the expansion of the Universe.

Galaxy clusters observed as part of a study that uses the massive objects as markers to determine the properties of dark energy
X-ray: NASA/CXC/Univ. of Alabama/A. Morandi et al; Optical: SDSS, NASA/STScI

A new technique to measure the properties of dark energy is using the similarities of different galaxy clusters as markers to calculate distances in the Universe.

The study found that the properties of dark energy have not changed over billions of years, and the technique could be used in future to learn more about dark energy and its role in the expansion of the cosmos.

Galaxy clusters are the largest structures in the Universe that are held together by gravity, and this new technique relies on the fact that the clusters’ outer edges are all similar in terms of their X-ray emission profiles and sizes. More massive specimens are simply scaled-up versions of less massive clusters.

This knowledge enables astronomers to measure their distances across billions of lightyears, which can be used to calculate how quickly the Universe has been expanding since the Big Bang.

The calculations are derived from Albert Einstein’s general theory of relativity, which states that the rate of expansion of the Universe is relative to the properties of dark energy plus the amount of matter contained in the cosmos, including the invisible and allusive substance known as dark matter.

If, however, the properties of dark energy and dark matter in the calculations are incorrect, then distant galaxy clusters appear larger or smaller than expected. Astronomers can then adjust the properties of dark energy and dark matter in their calculations so that they match observations.

The results of the study are showing that the properties of dark energy have not changed over billions of years.

320 galaxy clusters in all were observed during the study, using the Chandra X-ray Observatory and the Planck telescope, among others. The distances of the clusters from Earth range from 760 million lightyears to 8.7 billion lightyears.

"The nature of dark energy is one of the biggest mysteries in physics, so it's crucial to invent new tools for studying its properties, since different methods can have very different assumptions, strengths and weaknesses," said Morandi. "We think this new technique has the ability to provide a big leap forward in our understanding of dark energy."


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