COBE :: Science Results

Differential Microwave Radiometer (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.

The following image is similar to the June 1992 Physics Today cover picture, with the map including the dipole and Galaxy on the top, the dipole removed map in the middle, and the reduced map on the bottom. The dipole, a smooth variation between relatively hot and relatively cold areas from the upper right to the lower left, is due to the motion of the solar system relative to distant matter in the universe. The signals attributed to this variation are very small, only one thousandth the brightness of the sky.

The following image just shows the reduced map (i.e., both the dipole and Galactic emission subtracted). The cosmic microwave background fluctuations are extremely faint, only one part in 100,000 compared to the 2.73 degree Kelvin average temperature of the radiation field. The cosmic microwave background radiation is a remnant of the Big Bang and the fluctuations are the imprint of density contrast in the early universe. The density ripples are believed to have given rise to the structures that populate the universe today: clusters of galaxies and vast regions devoid of galaxies.

Far Infrared Absolute Spectrophotometer (FIRAS)

The cosmic microwave background (CMB) spectrum is that of a nearly perfect blackbody with a temperature of 2.725 +/- 0.001K. 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.

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. The solid curve shows the expected intensity from a single temperature blackbody spectrum, as predicted by the hot Big Bang theory. A blackbody is a hypothetical body that absorbs all electromagnetic radiation falling on it and reflects none whatsoever. The FIRAS data were taken at 34 positions equally spaced along this curve. The FIRAS data match the curve so exactly, with error uncertainties less than the width of the blackbody curve, that it is impossible to distinguish the data from the theoretical curve. These precise CMB measurements show that 99.97% of the radiant energy of the Universe was released within the first year after the Big Bang itself. All theories that attempt to explain the origin of large scale structure seen in the Universe today must now conform to the constraints imposed by these measurements. The results show that the radiation matches the predictions of the hot Big Bang theory to an extraordinary degree.

Diffuse Infrared Background Experiment (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.

False-color image of the near-infrared sky as seen by the DIRBE. Data at 1.25, 2.2, and 3.5 µm wavelengths are represented respectively as blue, green and red colors. The image is presented in Galactic coordinates, with the plane of the Milky Way Galaxy horizontal across the middle and the Galactic center at the center. The dominant sources of light at these wavelengths are stars within our Galaxy. The image shows both the thin disk and central bulge populations of stars in our spiral galaxy. Our Sun, much closer to us than any other star, lies in the disk (which is why the disk appears edge-on to us) at a distance of about 28,000 light years from the center.