| BOOMERANG:
Images |
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| Sound
waves in the embryonic Universe are revealed for the first time in
this image captured by the BOOMERANG balloon-borne telescope during
its maiden voyage around the Antarctic. The patterns visible in the
image are consistent with those that would result from sound waves racing
through the early universe, creating the structures that by now have evolved
into giant clusters and super-clusters of galaxies. The image records the
intense heat that filled the universe just after the Big Bang, which is
still present today as a faint glow of microwave radiation that fills the
sky. The first evidence of structure in this Cosmic Microwave Background
(CMB) was found in 1991 by NASA's Cosmic Background Explorer (COBE) satellite,
which mapped the entire sky with high sensitivity but coarse angular resolution
(upper left). The BOOMERANG image covers approximately 2.5% of the sky
with angular resolution 35 times that of COBE, revealing hundreds of complex
structures that are visible as tiny variations -- typically only 100 millionths
of a degree (0.0001 C) -- in the temperature of the CMB. Detailed analysis
of this image will determine the geometry of the universe to high precision,
and will shed light on the nature of the matter and energy that fill the
Universe.
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An image of the Primordial
Universe. Enormous structures in the early universe which are invisible
to the unaided eye become apparent when observed using a telescope sensitive
to mm-wave light. This image of approximately 1800 square degrees
of the southern sky was taken using the BOOMERANG telescope over a 10 day
period from December 1998 - January, 1999. For scale, the apparent size
of the moon is indicated on the bottom right of the page. In this picture,
we see the distant Universe as it makes its transition from a glowing 2700
deg C plasma to a perfectly transparent gas, approximately 14 billion years
ago, a mere 300,000 years after the Big Bang. The color scale of the image
has been enhanced to bring out the tiny 100 ppm temperature variations
in the primordial plasma. BOOMERANG is the first telescope with the resolution
and sensitivity required to image these variations, which have since evolved
into giant clusters and superclusters of galaxies today.
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The BOOMERANG Telescope
being readied for launch. With Mt. Erebus as a backdrop, NASA/NSBF
personnel inflate the 1 million m3 (28 million cubic foot) balloon
which will carry the BOOMERANG telescope on its 10 day trip around the
Antarctic continent. In order to make its exquisitely sensitive measurements,
BOOMERANG is lifted above 99% of the atmosphere to an altitude of 35km
(120,000 ft.). The continuous sunlight and stable air currents over Antarctica
enable 10 to 20 day long stratospheric balloon flights. This launch was
preceded by two months of assembly at McMurdo research station, and half
a decade of development and construction by a international team of researchers
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The CMB sky over Mt.
Erebus. In this fanciful picture, the CMB sky looms behind the prelaunch
preparations of BOOMERANG. The BOOMERANG images of the early universe have
been overlaid onto the sky to indicate what size that the fluctuations
would appear if a standard 35mm camera were sensitive to microwave light.
The color map of the CMB images has been changed here to aesthetically
match the rest of the picture. The CMB images and the prelaunch picture
are available separately.
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BOOMERANG images determine
the geometry of space. By observing the characteristic size of hot
and cold spots in the BOOMERANG images, the geometry of space can be determined.
Cosmological simulations predict that if our universe has a flat geometry,
(in which standard high school geometry applies), then the BOOMERANG images
will be dominated by hot and cold spots of around 1 degree in size (bottom
center). If, on the other hand, the geometry of space is curved, then the
bending of light by this curvature of space will distort the images. If
the universe is closed, so that parallel lines converge, then the images
will be magnified by this curvature, and structures will appear larger
than 1 degree on the sky (bottom left). Conversely, if the universe is
open, and parallel lines diverge then structures in the images will appear
smaller (bottom right). Comparison with the BOOMERANG image (top) indicates
that space is very nearly flat.
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The Spectrum of Primordial
Sound. The temperature variations in early universe seen in the BOOMERANG
images are due to sound waves in the primordial plasma. The angular spectrum
of these images shown here, reveals the characteristic size of the structures
that dominate the image. A peak in this spectrum at scales of ~ 1 degree,
as is seen here in the BOOMERANG data, indicates that the Universe is nearly
spatially flat. The data can be well fit by cosmological models that contain
non-baryonic matter in addition to normal, baryonic matter. One such model
is indicated by the solid blue curve. A generic feature of such models
is the presence of a harmonic series of additional peaks beyond the fundamental
peak at ~ 1 degree. The relative height of the second peak at ~ 1/2 degree
on the sky varies with the ballance of matter in the Universe contained
in normal or baryonic matter and non-baryonic matter.
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Cosmological Results
from BOOMERANG compared with Type 1a Supernovae Results. Shown here
are limits from BOOMERANG and Type Ia supernovae on the values of the average
density of space in matter (OmegaM, on the horizontal axis)
which slows the expansion of the Universe, and the density of the so-called
Dark Energy of empty space (OmegaLambda, on the vertical axis)
which causes the expansion of the universe to accelerate, preventing re
collapse. The BOOMERANG results are consistent with cosmological models
whose parameters lie within the blue region. This curve is concentrated
near the diagonal red line. From this we learn that, according to BOOMERANG
data, the Universe is cosmologically flat. As an excellent complement to
this, recent results from the study of S1a supernovae are consistent with
cosmological models which lie inside of the yellow region. If both measurements
are correct, then allowed models lie in the gree overlap region. This overlap
region indicates that our universe is cosmologically flat, started with
a Big Bang, and will not collapse again
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The micromesh bolometer,
reminicent of a spider's web, uses a free-standing micromachined mesh of
silicon nitride to absorb millimeter-wave radiation from the cosmic microwave
background. This design uses the minimum amount of material for optimal
performance. Millimeter-wave radiation is absorbed and measured as
a minute temperature rise in the mesh by a tiny Germanium thermistor.
Cooling the sensor to three tenths of a degree above absolute zero results
in the high sensitivity necessary to create the BOOMERANG maps.
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webmaster: Federico Nati - email: federico.nati@roma1.infn.it