Discovering Dark Energy through X- Rays

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Discovering Dark Energy through X- Rays


The accelerated expansion of the Universe and the discovery of Dark Energy are considered two of the greatest unsolved problems of modern astronomy. In the search for dark energy, X-ray telescopes will play a major role. XMM Newton and Chandra Telescope are currently playing a major role in searching the dark energy. There are two possible effects of dark energy on the universe. First is its effect on the rate of expansion and second is its impact on the large-scale structures (LSS). On large scale, the universe cannot be described through a single galaxy or star. If we keep zooming out the universe, we will find a star, then a group of stars, then the galaxy, then the group of galaxies. The farthest limit is a cluster of galaxies that expands billions of light-years (Cosmic Microwave Background). This is the Large Scale Structure of the Universe.

Astronomers, by studying the LSS can find the strength of gravity in the Universe. They have also created a theoretical model of dark energy through the LSS. Most of the theoretical models of dark energy concluded that as the universe expands, the process of gravity creating the large structures slows down.

The contribution of X-ray telescopes in discovering dark matter is by observing the galaxy clusters. X-ray study of clusters provides both, geometry and growth of the structure. X-ray observations through Chandra and Netwon have made a significant impact in creating a theoretical model of dark energy. In the past few years, astronomers have made significant progress in selecting the cluster sample and extracting the x-ray data at both low and high redshifts. The distance redshift relation of these clusters can be obtained through Sunyaev- Zel'dovich effect. The distance redshift relation is the best way to trace the evolution of the universe.

In the 1990s, the ROSAT mission made some great observations in the distant clusters. Its sensitivity and angular resolution were well suited to observe clusters at low redshift. ROSAT had some of the best X-ray astronomy instruments in it. Its PSPC (Position Sensitive Proportional Counters) were used to observe extragalactic clusters. The ROSAT observed over 266 galaxy clusters of different sizes. 

The observations by Chandra and XMM Newton provide the details like temperature, density and composition of the intracluster medium (ICM) over the wide range. Intracluster medium, in astronomy, is the superheated plasma that penetrates the galaxies. Most of the observations of Chandra includes high mass clusters. The density and temperature of gases show a very high level of regularity. Using the data from these observations and hydrostatic equilibrium equation astronomers can estimate the total mass of these clusters. Also, these data are useful to verify the numeric model of large cluster formation. 

X-ray observations from Chandra, ROSAT and Newton resulted in predictions of geometry and growth of cosmological structures. These cluster data independently proved the accelerated expansion of the universe, which shows that the properties of dark energy are very close to those predicted.    

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