A treasure trove of data released by NASA this week is giving astronomers insight into what the universe is made up of and how it developed, including that it is awash in a sea of weightless sub-atomic particles.
The data were collected by the Wilkinson Microwave Anisotropy Probe (WMAP), which measures a remnant of the early universe - its oldest light. The conditions of the early universe are imprinted on this light, which lost energy as the universe expanded over 13.7 billion years. Because of this energy loss WMAP now sees the light as microwaves.
By making accurate measurements of microwave patterns, WMAP has answered many longstanding questions about the universe's age, composition and development.
Sea of neutrinos
WMAP has found, for example, that the universe is awash in a sea of neutrinos, almost weightless sub-atomic particles that zip around at nearly the speed of light. Millions of cosmic neutrinos pass through you every second.
"A block of lead the size of our entire solar system wouldn't even come close to stopping a cosmic neutrino," said team member Eiichiro Komatsu of the University of Texas at Austin.
Neutrinos made up a much larger part of the early universe than they do today, according to the WMAP data.
Microwave light seen by WMAP from when the universe was only 380,000 years old, shows that, at the time, neutrinos made up 10 percent of the universe, atoms 12 percent, dark matter 63 percent, photons 15 percent, and dark energy was negligible. In contrast, estimates from WMAP data show the current universe consists of 4.6 percent atoms, 23 percent dark matter, 72 percent dark energy and less than 1 percent neutrinos.
This marks the first time that evidence for this so-called "cosmic neutrino background" has been gleaned from the microwaves.
Cosmic neutrinos existed in such huge numbers they affected the universe's early development. The hot and dense young universe was a nuclear reactor that produced helium. Theories based on the amount of helium seen today predict a sea of neutrinos should have been present when helium was made. The new WMAP data agree with that prediction, along with precise measurements of neutrino properties made by Earth-bound particle colliders.
Another breakthrough derived from WMAP data provide crucial new insights into the end of the "dark ages," when the first generation of stars began to shine. They provide clear evidence that the first stars took more than a half-billion years to create a cosmic fog.
The glow from these stars created a thin fog of electrons in the surrounding gas that scatters microwaves, in much the same way fog scatters the beams from a car's headlights.
"We now have evidence that the creation of this fog was a drawn-out process, starting when the universe was about 400 million years old and lasting for half a billion years," said WMAP team member Joanna Dunkley of the University of Oxford in the U.K. and Princeton University in Princeton, N.J.
WMAP data also places tight constraints on the astonishing burst of growth in the first trillionth of a second of the universe, called "inflation", when ripples in the very fabric of space may have been created. Some versions of the inflation theory now are eliminated. Others have picked up new support.
"The new WMAP data rule out many mainstream ideas that seek to describe the growth burst in the early universe," said WMAP principal investigator, Charles Bennett, of The Johns Hopkins University in Baltimore, Md. "It is astonishing that bold predictions of events in the first moments of the universe now can be confronted with solid measurements."
The findings taken from the WMAP data were detailed in a set of seven scientific papers submitted to the Astrophysical Journal.
- The Universe: 365 Days
- About WMAP and the Cosmic Microwave Background
- All About the Universe