Using a powerful new instrument at the South Pole, a team of
cosmologists has produced the most detailed images of the early
Universe ever recorded. The research team, which was funded by the
National Science Foundation (NSF), has made public their measurements
of subtle temperature differences in the Cosmic Microwave Background
(CMB) radiation. The CMB is the remnant radiation that escaped from
the rapidly cooling Universe about 400,000 years after the Big Bang.
Images of the CMB provide researchers with a snapshot of the Universe
in its infancy, and can be used to place strong constraints on its
constituents and structure. The new results provide additional
evidence to support the currently favored model of the Universe in
which 30 percent of all energy is a strange form of dark matter that
doesn’t interact with light and 65 percent is in an even stranger
form of dark energy that appears to be causing the expansion of the
Universe to accelerate. Only the remaining five percent of the
energy in the Universe takes the form of familiar matter like that
which makes up planets and stars.
The researchers developed a sensitive new instrument, the Arcminute
Cosmology Bolometer Array Receiver (ACBAR), to produce
high-resolution images of the CMB. ACBAR’s detailed images reveal
the seeds that grew to form the largest structures seen in the
Universe today. These results add to the description of the early
Universe provided by several previous ground-, balloon- and
space-based experiments. Previous to the ACBAR results, the most
sensitive, fine angular scale CMB measurements were produced by the
NSF-funded Cosmic Background Investigator (CBI) experiment observing
from a mountaintop in Chile.
William Holzapfel, of the University of California at Berkeley and
ACBAR co-principal investigator, said it is significant that the new
ACBAR results agree with those published by the CBI team despite the
very different instruments, observing strategies, analysis
techniques, and sources of foreground emission for the two
experiments. He added that the new data provide a more rigorous test
of the consistency of the new ACBAR results with theoretical
predictions.
“It is amazing how precisely our theories can explain the behavior of
the Universe when we know so little about the dark matter and dark
energy that comprise 95 percent of it,” said Holzapfel.
The dark energy inferred from the ACBAR observations may be
responsible for the accelerating expansion of the Universe. “It is
compelling that we find, in the ancient history of the Universe,
evidence for the same dark energy that supernova observations find
more recently,” said Jeffrey Peterson of Carnegie Mellon University.
The construction of the ACBAR instrument and observations at the
South Pole were carried out by a team of researchers from the
University of California, Berkeley, Case Western Reserve University,
Carnegie Mellon University, the California Institute of Technology,
Jet Propulsion Laboratory (JPL), and Cardiff University in the United
Kingdom. Principle investigators Holzapfel and John Ruhl at Case
Western led the effort, which built and deployed the instrument in
only two years.
ACBAR is specifically designed to take advantage of the unique
capabilities of the 2.1-meter Viper telescope, built primarily by
Jeff Peterson and collaborators at Carnegie Mellon and installed by
NSF and its South Pole Station in Antarctica. The receiver is an
array of 16 detectors built by Cal Tech and the JPL that create
images of the sky in 3-millimeter wavelength bands near the peak in
the brightness of the CMB. In order to reach the maximum possible
sensitivity, the ACBAR detectors are cooled to two-tenths of a degree
above absolute zero, or about -273 degrees Celsius (-459 Fahrenheit).
ACBAR has just completed its second season of observations at the
South Pole. Researcher Mathew Newcomb kept the telescope observing
continuously during the six-month-long austral winter, despite
temperatures plunging below -73 degrees Celsius (-100 Fahrenheit).
The construction of ACBAR and Viper was funded as part of the NSF
Center for Astrophysical Research in Antarctica. The U.S. Antarctic
Program provides continuing support for telescope maintenance,
observations, and data analysis. NSF’s Amundsen-Scott South Pole
Station is ideally suited for astronomy, especially observations of
the CMB. The station is located at an altitude of approximately
3,000 meters (10,000 feet), atop the Antarctic ice sheet. Water
vapor is the principal cause of atmospheric absorption in broad
portions of the electromagnetic spectrum from near infrared to
microwave wavelengths. The thin atmosphere above the station is
extremely cold and contains almost no water vapor. “Our atmosphere
may be essential to life on Earth,” said Ruhl, “but we’d love to get
rid of it. For our observations, the South Pole is as close as you
can get to space while having your feet planted firmly on the ground.”
Papers describing the ACBAR CMB angular power spectrum and the
constraints it places on cosmological parameters have been submitted
to the Astrophysical Journal for publication.
For pictures or more information and drafts of the submitted papers,
see:
http://cosmology.berkeley.edu/group/swlh/acbar
