Cosmic Background Explorer
The COBE satellite was developed by NASA's Goddard Space
Flight Center to measure the diffuse infrared and microwave
radiation from the early universe to the limits set by our
astrophysical environment. It was launched November 18, 1989
and carried three instruments, a Diffuse
Infrared Background Experiment (DIRBE) to search for the
cosmic infrared background radiation, a Differential
Microwave Radiometer (DMR) to map the cosmic radiation
sensitively, and a Far Infrared
Absolute Spectrophotometer (FIRAS) to compare the spectrum
of the cosmic microwave background radiation with a precise
blackbody. Each COBE instrument yielded a major cosmological
discovery:
- DIRBE - Infrared absolute
sky brightness maps in the wavelength range 1.25 to 240
microns were obtained to carry out a search for the cosmic
infrared background (CIB). The CIB was originally
detected in the two longest DIRBE wavelength bands, 140
and 240 microns, and in the short-wavelength end of the
FIRAS spectrum. Subsequent analyses have yielded detections
of the CIB in the near-infrared DIRBE sky maps. The CIB
represents a "core sample" of the Universe; it
contains the cumulative emissions of stars and galaxies
dating back to the epoch when these objects first began
to form. The COBE CIB measurements constrain models of the
cosmological history of star formation and the buildup over
time of dust and elements heavier than hydrogen, including
those of which living organisms are composed. Dust has played
an important role in star formation throughout much of cosmic
history.
- DMR - The CMB was found
to have intrinsic "anisotropy" for the first time,
at a level of a part in 100,000. These tiny variations in
the intensity of the CMB over the sky show how matter and
energy was distributed when the Universe was still very
young. Later, through a process still poorly understood,
the early structures seen by DMR developed into galaxies,
galaxy clusters, and the large scale structure that we see
in the Universe today.
- FIRAS - The cosmic microwave
background (CMB) spectrum is that of a nearly perfect blackbody
with a temperature of 2.725 +/- 0.002 K. This observation
matches the predictions of the hot Big Bang theory extraordinarily
well, and indicates that nearly all of the radiant energy
of the Universe was released within the first year after
the Big Bang.