NASA has released five years of data collected by the
Wilkinson Microwave Anisotropy Probe
that refine our understanding of the universe and its
development. The treasure trove of information
includes at least three major findings:
New evidence that a sea of cosmic
neutrinos permeates the universe.
"We are living in an extraordinary time," said Gary
Hinshaw of NASA's Goddard Space Flight
Center in Greenbelt, Md. "Ours is the first generation in
human history to make such detailed and far-
reaching measurements of our universe."
Clear evidence that the first
stars took more than a half-billion years to create a
Tight new constraints on the burst
of expansion in the universe's first trillionth of a
Charles Bennett, a professor in the Henry A. Rowland Department
of Physics and Astronomy at
Johns Hopkins, is WMAP principal investigator.
WMAP measures a remnant of the early universe: its
oldest light, on which are imprinted the
conditions of the early times. As the universe expanded
over 13.7 billion years, this light lost energy,
so WMAP now sees the light as microwaves. By making
accurate measurements of microwave patterns,
WMAP has answered many long-standing questions about the
universe's age, composition and
The universe is awash in a sea of cosmic neutrinos.
These almost weightless sub-atomic particles
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 science team member Eiichiro
Komatsu, of the University of Texas at Austin.
WMAP has found evidence for this so-called "cosmic
neutrino background" from the early
universe, when neutrinos made up a much larger part of the
universe than they do today.
Microwave light seen by WMAP from when the universe
was only 380,000 years old shows that
neutrons 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.
Cosmic neutrinos existed in such huge numbers that
they affected the universe's early
development. That, in turn, influenced the microwaves that
WMAP observes. WMAP data suggest, with
greater than 99.5 percent confidence, the existence of the
cosmic neutrino background — the first
time this evidence has been gleaned from the cosmic
Much of what WMAP reveals about the universe is
because of the patterns in its sky maps. The
patterns arise from sound waves in the early universe. As
with the sound from a plucked guitar string,
there is a primary note and a series of harmonics, or
overtones. The third overtone, now clearly
captured by WMAP, helps to provide the evidence for the
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
Another breakthrough derived from WMAP data is clear
evidence that the first stars took
more than a half-billion years to create a cosmic fog. The
data provide crucial new insights into the
end of the "dark ages," when the first generation of stars
began to shine. 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 and Princeton
University. "These measurements are
currently possible only with WMAP."
A third major finding arising from the new WMAP data
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," Bennett said. "It is astonishing that
bold predictions of events in the first
moments of the universe now can be confronted with solid
Results of the five-year WMAP data were issued in a
set of seven scientific papers submitted
to the Astrophysical Journal.
Prior to the release of the new data, WMAP already had
made a pair of landmark finds. In
2003, the probe's determination that there is a large
percentage of dark energy in the universe
erased remaining doubts about dark energy's very existence.
That same year, WMAP pinpointed the
13.7 billion year age of the universe.
Additional WMAP science team institutions are the
Canadian Institute for Theoretical
Astrophysics, Columbia University, University of British
Columbia, ADNET Systems, University of
Chicago, Brown University and UCLA.