- Astrophysicists have taken another major step in depicting
the universe in its infancy. The first results from a balloon-borne
experiment peering back to a time shortly after the big bang
provide confirmation of a mysterious "dark matter" and "dark
energy" that make up most of the cosmos.
MAXIMA team, from left to right: team leader Paul Richards
of Berkeley; Shaul Hanany of the University of Minnesota;
UC Berkeley physics grad student Celeste Winant; Adrian
Lee of Berkeley's Center for Particle Astrophysics; and
Bahman Rabii, also a physics graduate student at UC Berkeley.
of the experiment, an international collaboration called the
Millimeter Anisotropy eXperiment IMaging Array (MAXIMA), directed
by the University of California, Berkeley, are contained in
two papers submitted Monday, May 8, to Astrophysical Journal
Letters and scheduled for posting Tuesday on the internet
results confirm results announced last month by another group
after analysis of data from a balloon-borne experiment called
Balloon Observations Of Millimetric Extragalactic Radiation
and Geophysics (BOOMERANG), and extend these results to smaller
angular scales on the sky. The MAXIMA map is the highest resolution
map of the cosmic microwave background yet published.
provide strong evidence that the universe is flat, with a
large-scale geometry just like the Euclidean geometry everyone
learns in high school. However, only about 5 percent of its
mass and energy is comprised of ordinary matter - the stuff
of which the Earth, the stars and humans are made. The remainder
is either cold dark matter - the unseen mass that holds galaxies
together - or dark energy, a mystifying pressure or repulsive
force that seems to be accelerating the expansion of the universe.
The dark energy often is referred to as the cosmological constant.
of cosmological theories, those involving inflation, dark
matter and a cosmological constant, fit our data extremely
well," said team leader Paul Richards, UC Berkeley professor
of physics. Inflation is the most popular cosmological theory
describing the early history of the universe.
a good confirmation of the standard cosmology, and a large
triumph for science, because we are talking about predictions
made well before the experiment, about something as hard to
know as the very early universe."
team, consisting of 22 collaborators from 13 institutions
and five countries, is funded by the National Science Foundation
and the National Aeronautics and Space Administration, with
the Department of Energy supporting the data analysis.
some members are common both to the MAXIMA and to the BOOMERANG
teams, the two analyses were done completely independently,"
noted Shaul Hanany, professor of physics at the University
of Minnesota, Minneapolis, and first author of one of the
papers. "The fact that these independent experiments give
such similar results is the best indication that we are both
getting the science right."
map of the thermal fluctuations in the cosmic microwave
background with a resolution of 10 arcminutes, from the
first flight of MAXIMA. The map contains 15,000 pixels,
each 5 arcminutes on a side.
are extremely difficult experiments, and yet the data from
MAXIMA and BOOMERANG show spectacular agreement," added cosmologist
Adrian Lee, a leader of the MAXIMA project from the NSF Center
for Particle Astrophysics and the Space Sciences Laboratory,
both at UC Berkeley.
theories refer to an event that happened an infinitesimally
small fraction of a second after the big bang, an explosive
event that most astronomers believe kicked off our universe
some 10-20 billion years ago. At that moment, the expanding
universe underwent a rapid inflation that smoothed out the
matter and energy. Only afterwards did pressure waves or sound
waves imprint detailed information about the nascent universe
on the clumps of hot, dense matter created during inflation.
history is invisible to us, but clues come from a time about
300,000 years later, when the universe cooled to approximately
3,000 Kelvin, allowing atoms of hydrogen to form. Light suddenly
was freed from constant collision with charged particles,
and flashed us a snapshot of the hot and cold clumps at that
heat from that event cooled as the universe continued to expand,
until today the microwave background is a mere 2.7 Kelvin,
or 454 degrees Fahrenheit below zero. The hot and cold spots
vary by a few parts per 100,000. MAXIMA and BOOMERANG both
measured the temperature variations of the cosmic microwave
background, producing thermal maps of the universe 300,000
years after the big bang.
of the spots in the thermal map told the cosmologists immediately
one important parameter of the universe, its geometry or curvature.
Both experiments saw spots clustered in a size range of about
one degree across, indicating a flat universe like the ancient
Greek geometer Euclid described more than 2,300 years ago.
That type of geometry, the most familiar to us, is characterized
by parallel lines that always remain the same distance apart.
universe, akin to the two-dimensional surface of a sphere
where parallel lines eventually cross, would produce larger
spots; an open universe, in which parallel lines always diverge,
would produce smaller spots.
with recent data on the universe obtained from studies of
distant supernovas, the data also support the inflationary
theory of the universe. Specifically, the experiments peg
the amount of normal matter in the universe at about 5 percent;
the amount of dark matter at about 30 percent; and the amount
of dark energy- the cosmological constant - at about 65 percent.
probably the most interesting result of all these experiments,"
Hanany said. "The combination of our data with the data from
supernovas is very powerful evidence that we need something
like the cosmological constant to describe our universe. New
physics may be required to explain the origin of the cosmological
constant was something Albert Einstein threw into his equations
of the universe and subsequently tossed out as a mistake.
The surprising supernova results of the past few years resurrected
the idea, since the constant can describe a universe whose
expansion is accelerating.
noted that while the thermal map of the sky is a "pretty picture,"
most of the information comes from a detailed statistical
analysis of the sky data along with data at large angular
scales from the COBE mission. Using supercomputers at the
Department of Energy's National Energy Research Scientific
Computing Center (NERSC) at Lawrence Berkeley National Laboratory,
the MAXIMA team calculated the power spectrum of the sky map,
which is essentially the range of sizes of the hot and cold
spots in the microwave background. Just as a cluster around
one degree indicates a flat universe, clusters at smaller
angular sizes are a hallmark of inflationary theories.
the MAXIMA results cannot unambiguously identify other peaks
in the power spectrum, MAXIMA was able to derive other information
that strongly supports inflation. Among these is a zero "tilt,"
which essentially means that, immediately after inflation,
the fluctuations in the energy in the universe were uniform
over all size scales.
theories make two main predictions," Lee said. "One is a flat
universe. The other is that the power spectrum has no tilt.
MAXIMA supports both of these predictions."
also noted that the number - about 5 percent - obtained for
the fraction of the universe made up of ordinary matter, called
baryons, fits beautifully with entirely independent estimates
from the theory of nucleosynthesis in stars.
of people are skeptical of cosmology, so when your results
show this type of agreement, you have more confidence in your
theories," he said.
first became aware of the cosmic background radiation in 1965,
with the accidental discovery of microwave emissions from
all directions of the sky. This was taken as proof of the
big bang, and theorists created numerous theories over the
years to explain the evolution of the universe from its explosive
the Cosmic Background Explorer (COBE) satellite provided the
first evidence that the microwave glow is not uniformly 2.7
Kelvin, but varies by as much as 100 millionths of a Kelvin
above or below the average - evidence of clumps and wrinkles
in the very early universe. These clumps of matter and energy
presumably evolved into the clusters and superclusters of
galaxies we see today.
small experiments since then have measured the size of these
variations, hinting at a flat universe. But MAXIMA and BOOMERANG
have given cosmologists far clearer evidence for this, Richards
said. COBE obtained a low-resolution picture of the entire
sky, accurately measuring the large-scale clumps, and is complementary
to the MAXIMA data. MAXIMA looked with finer resolution at
an area representing 0.3 percent of the sky - a spot about
11 degrees on a side, or 22 times broader than the full moon
- in a northern region of the sky near the constellation Draco.
used for the analysis reported today were obtained from the
first flight of MAXIMA on Aug. 2, 1998, out of the National
Scientific Ballooning Facility in Palestine, Texas. The balloon,
launched at sunset, flies at about 130,000 feet for one night
- 7-10 hours - and is returned to the ground by a parachute.
The 1.3 meter telescope focuses the microwave radiation on
detectors cooled to one tenth of a degree Kelvin by high-tech
refrigerators developed by Richards' group. The detectors
can sample the sky at angular resolutions from 5 degrees to
1/6 degree. COBE could get no smaller than 7 degrees.
which started as a collaboration with MAXIMA, split off to
pursue a riskier approach - launching from a ballooning facility
in Antarctica in order to observe for10 days or more, at the
cost of flying less often, typically at two to three year
intervals. MAXIMA, launched from the U.S., can fly once or
twice a year, is more sensitive and looks at a smaller area
of the sky with finer detail, while BOOMERANG gathers data
over a larger area of sky.
2 flew in June 1999 and observed roughly twice the area that
MAXIMA 1 observed. MAXIMA 3 will fly in the fall of this year
and will attempt to measure the polarization of the cosmic
background radiation, which has never been observed.
radiation is polarized is another prediction of inflationary
theories," Hanany said. "Polarization measurements are the
new frontier in cosmic microwave background research."
analysis of the data from MAXIMA 1 and 2, combined with the
1992 COBE data and eventually the BOOMERANG data, should provide
better measurements of all the cosmological parameters, said
cosmologist Adrian Lee.
is still a lot more we can get from the MAXIMA data. We're
looking for gold in those Doppler hills," he said.
information can be found on the MAXIMA web page: http://cfpa.berkeley.edu/group/cmb/
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