One of the most important space probes of the century is the Wilkinson Microwave Anisotropy Probe (WMAP) launched in 2001 to measure the temperature differences in the Cosmic Microwave Background (CMB) radiation -the 14-billion year old Big Bang's remnant radiant heat . The anisotropies then in turn are used to measure the universe's geometry, content, and evolution; and, perhaps most importantly, to test the Big Bang model, and the cosmic inflation theory. WMAP data seem to support a universe that is dominated by dark energy in the form of a cosmological constant.
As the Universe cooled it underwent a series of phase transitions, analogous to water freezing into ice. Many transitions cannot occur consistently throughout space, giving rise in some theories to imperfections in the structure of the cooling material known as cosmic textures.
If produced in the early Universe, textures would interact with light from the CMB to leave a set of characteristic hot and cold spots. If detected, such signatures would yield invaluable insight into the types of phase transitions that occurred when the Universe was a fraction of a second old, with drastic implications for particle physics.
An earlier study, published in Science in 2007, provided a tantalising hint that a CMB feature known as the "Cold Spot" could be due to a cosmic texture. However, the CMB Cold Spot only comprises around 3% of the available sky area, and an analysis using the full microwave sky had not been performed.
The new study, published today in Physical Review Letters, places the best limits available on theories that produce textures, ruling out at 95% confidence theories that produce more than six detectable textures on our sky.
"If textures were observed, they would provide invaluable insight into the way nature works at tremendous energies, shedding light on the unification of the physical forces," said Stephen Feeney, from the UCL Department of Physics and Astronomy and lead author. "The tantalizing hints found in a previous small-scale search meant it was extremely important to carry out this full-sky analysis."
"Although there is no evidence for these objects in the WMAP data, this is not the last word: in a few months we will have access to much better data from the Planck satellite," said co-author Matt Johnson, from the Perimeter Institute, Canada. "Whether we find textures in the Planck data or further constrain the theories that produce them, only time will tell!"
A 25-degree region of the Cosmic Microwave Background emission around the region of the WMAP cold spot (circled below). The colors represent very small variations (parts in 100,000) around the average temperature of 2.7 degrees above absolute zero, with blue colors being colder. The data is from NASA's WMAP satellite.
The image at the top page is simulation by the NASA/WMAP Science Team of a 10 degree patch of the sky as it would have appeared between 100 years and 378,000 years after the big bang, if the plasma were transparent at that time.
The Daily Galaxy via ucl.ac.uk