London, March 6 : A NASA satellite mission has confirmed the theory that the universe is filled with a fluid of cold neutrinos that remain almost entirely aloof from ordinary matter.
Known as the Wilkinson Microwave Anisotropy Probe (WMAP), the mission measures the composition of the universe by observing the cosmic microwave background, radiation that was emitted just 380,000 years after the big bang.
According to a report in New Scientist, the mission has determined that the universe is submerged in a sea of undetectable particles called neutrinos, left over from the first few seconds of the big bang.
Cosmologists think that in the hot, dense, young universe, neutrinos should have been created in high-energy particle collisions. About two seconds after the big bang, the cauldron of colliding particles would have cooled down so much that most would not have had enough energy to interact strongly with neutrinos. The neutrinos would then have "de-coupled" from other matter and radiation.
In theory, they should still be buzzing around, a soup of slippery particles that by today has been chilled to a temperature of only 1.9, a Celsius above absolute zero.
Now WMAP has found evidence of this by building up a picture of the cosmic microwave background radiation, which carries a detailed imprint of the state of the universe 380,000 years after the big bang.
In particular, it reveals the pattern of density fluctuations in space, the "texture" of the early universe.
Traveling at nearly the speed of light, neutrinos should have discouraged matter from forming tight clumps, and so smoothed out the texture of the universe slightly.
The WMAP data clearly show this smoothing effect, implying that those fast-flowing neutrinos formed about 10% of all the energy in the 380,000-year-old universe.
"In 2005, another analysis also provided evidence for a cosmic neutrino background, but it relied on combining WMAP data from other sources, and making some assumptions about other cosmological parameters," said Eiichiro Komatsu of the University of Texas in Austin, US, lead author of a study about the result.
Now that WMAP has collected five years' worth of data, it is enough to show firm evidence of the neutrino background on its own.