CXC: Probing Dark Energy with Galaxy Clusters

[bystander]

"Russian Doll" Galaxy Clusters Reveal Information About Dark Energy
NASA | MSFC | SAO | Chandra X-ray Observatory | 2016 Apr 28

[img3="Credit: X-ray: NASA/CXC/Univ. Alabama/A. Morandi et al;
Optical: SDSS, NASA/STScI/Hubble"]http://chandra.si.edu/photo/2016/clusters/clusters.jpg[/img3][hr][/hr]

These four galaxy clusters were part of a large survey of over 300 clusters used to investigate dark energy, the mysterious energy that is currently driving the accelerating expansion of the Universe, as described in our latest press release. In these composite images, X-rays from NASA's Chandra X-ray Observatory (purple) have been combined with optical light from the Hubble Space Telescope and Sloan Digital Sky Survey (red, green, and blue).

Researchers used a novel technique that takes advantage of the observation that the outer reaches of galaxy clusters, the largest structures in the universe held together by gravity, show similarity in their X-ray emission profiles and sizes. That is, more massive clusters are simply scaled up versions of less massive ones, similar to Russian dolls that nest inside one another.

The amount of matter in the Universe, which is dominated by the unseen substance called dark matter, and the properties of dark energy (what astronomers call cosmological parameters) affect the rate of expansion of the Universe and, therefore, how the distances to objects change with time. If the cosmological parameters used are incorrect and a cluster is inferred to be traveling away faster than the correct value, then a cluster will appear to be larger and fainter due to this "Russian doll" property. If the cluster is inferred to be traveling away more slowly than the correct value, the cluster will be smaller and brighter than a cluster according to theory.

These latest results confirm earlier studies that the amount of dark energy has not changed over billions of years. They also support the idea that dark energy is best explained by the "cosmological constant," which Einstein first proposed and is equivalent to the energy of empty space. ...

Probing dark energy via galaxy cluster outskirts - Andrea Morandi, Ming Sun

• Monthly Notices of the RAS 457(3):3266 (2016 Apr 11) DOI: 10.1093/mnras/stw143
  arXiv.org > astro-ph > arXiv:1601.03741 > 14 Jan 2016 (v1), 04 Feb 2016 (v3)