Dark energy is the second most interesting mystery in our universe at the moment, the first being the properties of the Higgs boson and the third being the nature of the wily little oscillating neutrino. When it was discovered in the 1990s that the Universe is expanding at an accelerating rate, opposing previous theory, it was posited that a “dark” (meaning not visible to present instruments and detection techniques) energy was responsible for the force propelling the accelerated expansion. Various studies have attempted to identify dark emery, and the dark matter that generates it, with each study adding somewhat to the understanding of this force. For example, one such study revealed a halo of dark energy around galaxies that is posited to bound and define the spin shapes of the galaxies.
In 2008, a team of scientists headed by Giannantonio, Crittenden, Nichol, and Ross applied the integrated Sachs-Wolfe (ISW) effect to the problem of proving the existence of dark energy and came up with surprising results that were not, however, without emphatic critics. The ISW effect states that cosmic microwave background (CMB) radiation, resulting from the Universe’s earliest particle interactions, will take on a blue color when it passes through the energic gravitational fields of matter. The Giannantonio team wanted to know if this would be the case even if the energic gravitational field is dark (i.e., dark energy).
The 2008 results were what the ISW effect predicted: the areas around galaxies where dark energy had previously been indicated showed blue based on sky map analyses undertaken by the team. In 2010, Sawangwit et al. raised the question of “systematic contaminations of the data” suggesting that galaxy local contaminants, like space dust, had skewed the results giving the appearance of dark energy where there was, in fact, none. It was, therefore, further suggested that Giannantonio et al.’s method was faulty, producing unreliable results.
Consequently, the Giannantonio team revisited their experiment, calculations and analyses. They incorporated additional measures to reveal any valid systematic contaminations to increase certainty in their results. Specifically, they used “randomly rotating [sky] maps” (Giannantonio et al.) to obtain correlating data sets that would identify directional inconsistencies and indicate contamination identifiable from one direction though not from other directions. In addition, they employed updated analyses data sets and new, more precise, CMB and large-scale structure of the Universe (LSS) sky map data sets. The results yield a surprisingly high 99.996% certainty of having identified and located dark energy, which is the gravitational energy emanating from dark matter. Now that there is 99.996% certain that dark energy is real, the question remains: “What is it?”
Sources: Jon Bardin. “New study sheds light on dark energy.” Los Angeles Times. September 13, 2012.
Tommaso Giannantonio, Robert Crittenden, Robert Nichol, Ashley J. Ross. “The significance of the integrated Sachs-Wolfe effect revisited.” Monthly Notices of the Royal Astronomical Society. September 2012.