The Dark Energy Survey has taken its first image as of the 12th September 2012 of the Fornax galaxy cluster. The 570 million pixel camera used for the survey takes a shot which covers an area of the sky around 20 times larger than the full moon. The survey will eventually cover 100,000 galaxies and around 4,000 type 1a supernovae.
The survey is looking into the hypothesised Dark Energy which makes up just over 70% of the universe. Dark Energy is believed to exist due to the findings in 1998 by Saul Perlmutter that the redshifts of distant type 1a supernovae pointed towards an acceleration in the expansion of the universe. In order for this acceleration to occur a force must exist which acts against the overall gravitational attraction of matter but is also 3 times as much. Therefore Dark Energy is said to be spaced evenly throughout the universe with a constant density.
The discovery of this accelerated expansion won Saul the 2011 Nobel Prize for Physics and now this Survey’s job is to ask the question of what this energy is and if there is any way of directly detecting it. The Survey will use a number of techniques to investigate this Dark Energy, the conventional technique of taking the redshift of type 1a supernovae to plot the rate of expansion and the mapping of many galaxy clusters to look at early formation.
Type 1a supernovae are so useful due to there similar luminosity curves which is caused by the way they are produced. In a binary system of an ordinary star and a white dwarf, the dwarf accretes matter from the other star until its own mass is greater than that of the Chandrasekhar limit (around 1.4 solar masses) at this point the electron degeneracy can no longer hold the gravtational collapse and the white dwarf “explodes” in a supernova. As this always happens at the same mass the luminosity curve is always the same, this means that this type of supernova can be used as a standard candle in the sky by which a distance and redshift can be easily measured.
What is this Dark Energy and Dark Matter? With the discovery of the Higgs Boson behind us this is the next big question which must have an answer if we are to have a more complete picture of our universe…