Are Galaxy clusters the ones creating the cosmic background radiation?

Answer 1

Not creating, but perhaps interferring with. You're thinking of the Sunayev-Zel'dovich effect. That's inverse Compton scattering off galactic clusters, which can scatter background radiation and make areas of the sky appear cooler than they are.

Answer 2

No, the cosmic background radiation is the residual image of the Big Bang. It predates everything in the universe.

Answer 3

Cosmic background radiation
A nearly uniform flux of microwave radiation that is believed to permeate all of space. The discovery of this radiation in 1965 by A. Penzias and R. W. Wilson has had a profound impact on understanding the nature and history of the universe. The interpretation of this radiation as the remnant fireball from the big bang by P. J. E. Peebles, R. H. Dicke, R. G. Roll, and D. T. Wilkinson, and their correct prediction of the spectrum to be that of a blackbody, was one of the great triumphs of cosmological theory. The flight of the Cosmic Background Explorer (COBE) satellite has both verified the basic nature of the radiation and given deep insight into the mechanism of formation of galaxy clusters in the early universe and the presence of dark matter.

In the theory of the big bang, the universe began with an explosion 10–15 billion years ago. This big bang was not an explosion of matter into empty space but an explosion of space itself. The early universe was filled with dense, hot, glowing matter; there was no region of space free of matter or radiation. (This state is reflected in the present universe by the fact that space is more or less uniformly filled with galaxies; galaxy clusters and holes between clusters are believed to have grown from gravitational instabilities during the expansion.) The explosion of space increased the volume of the matter and radiation and thus reduced the density and temperature. The initial temperature was so high that even for several hundred thousand years after the initial explosion the universe was still as hot as the surface of the present-day Sun. At this temperature the matter of the universe was in the form of a plasma of electrons, protons, alpha particles (helium nuclei), and photons. The photons were strongly absorbed and reemitted by the electrons, and their spectrum was similar to that of the Sun. About 500,000 years after the initial explosion, the expansion caused the temperature to drop enough that the electrons and protons recombined to form hydrogen atoms. Unlike the previous plasma, which was opaque to light, neutral hydrogen is transparent. From that time (called the time of the decoupling or of recombination) until now, the cosmic photons have been traveling virtually unscattered, carrying information about the nature of the universe at the time of the decoupling. See also Big bang theory.

To an observer moving with the plasma, the photons have a blackbody spectrum with a characteristic temperature of a few thousand kelvins. (A blackbody spectrum is the characteristic emission from a perfectly absorbing object heated to the characteristic temperature. The orange glow emitted from a heated pan is approximately blackbody, as is the light emitted from the filament of a light bulb or from the surface of the Sun.) Although the glow from the plasma is in the visible region, as a result of the recessional velocity of the plasma from the Earth the radiation is redshifted from the visible into the microwave region, with a characteristic temperature of 3 K (5°F above absolute zero, ?459.67°F). Detection of the radiation is really the observation of the shell of matter that last scattered the radiation. See also Heat radiation; Redshift.

The microwave radiation is coming from the most distant region of space ever observed, and was emitted earlier in time than any other cosmological signal. The radiation was originally termed cosmic background radiation because the discoverers foresaw that it would cause a background interference with satellite communications, but the term has taken on a vivid new meaning: the radiating shell of matter forms the spatial background in front of which all other astrophysical objects, such as quasars, lie. Until methods are devised to detect the neutrinos or gravity waves that were decoupled earlier, there will be no direct means of viewing beyond this background. See also Gravitational radiation; Neutrino.

Subsequent to its discovery, experimental work on the microwave background has been concerned primarily with the measurement of the radiation's color (its spectrum of intensity at different frequencies) and with its isotropy (its intensity as a function of direction in the sky). Results from the COBE satellite showed that the spectrum is that of a blackbody, at a temperature above absolute zero of 2.735 ± 0.060 K, to better than 1% accuracy. The lack of deviations places strong limits on the nature of material present at the time of decoupling, just a half million years after the creation of the universe.

Measurements showed that the radiation was isotropic to better than 1%. This uniformity posed a difficult problem for cosmological theory, since according to the simple big bang theory the different parts of the sky that gave rise to the microwave background had not been close enough together to reach an equilibrium temperature. Thus there was no way to understand how the intensity could be uniform. This theoretical problem was solved by a variation on the big bang theory called the inflationary universe model. In this picture the early universe was much smaller than had previously been supposed, giving it time to attain a uniform temperature; the rapid expansion of the universe occurred at a later time, the period of inflation. See also Inflationary universe cosmology.

A map of intensity produced by the COBE satellite displays a smooth yin-yang pattern, which is the cosine variation from the 600-km/s (370-mi/s) motion of the Milky Way Galaxy. The variation is only about 3.4 mK, or about 0.1% as large as the constant 2.7-K past. The velocity of the Milky Way Galaxy is believed to result from its gravitational acceleration toward the center of a large local supercluster of galaxies. See also Doppler effect; Galaxy, external; Universe.

In 1992 the COBE team announced that they had found small variations in the microwave map that appear to be cosmological in origin. The map of intensity with the cosine term removed displays a bright horizontal band which comes from synchrotron emission in the Milky Way Galaxy. The most exciting regions of the plot are the marbled areas above and below the synchrotron stripe, which the COBE team called ripples in the radiation. These ripples are believed to be the first indications that the early universe was not completely uniform. The structure has a magnitude of approximately 15–30 ?K, a factor of 200,000 times smaller than the 2.7-K radiation itself.

The inflationary universe model accounts for the uniformity of the radiation but still leaves the puzzle that the present universe is highly nonuniform, with most of the mass clumped into stars, galaxies, and clusters of galaxies. Most astrophysicists believe that the clumping came about from the mutual gravitational attraction of the matter created in the big bang. The cosmological anisotropy observed by the COBE satellite is interpreted as the early sign of the clumping, taking place a half million years after the creation of the universe.

Theories of galaxy formation must postulate large amounts of dark, unseen matter in order to provide the strong gravitational fields necessary for sufficient clumping. The nature of this matter is unknown, but the matter must be more massive than all that observed in stars and galaxies. The radiation coming from the otherwise unseen clumps undergoes a gravitational redshift, according to the general theory of relativity, and it is this effect that COBE is believed to be observing. These residual lumps are consistent in magnitude and form with that predicted by the inflationary universe version of the big bang theory. Thus the ripples observed in the radiation are in fact a map of the distribution of dark matter in the very early universe.