Zeldovitch pancake – Wikipedia

The theoretical notion of Zeldovitch crepe relates to a gas condensation resulting from a fluctuation of the primordial density that followed the Big Bang. In 1970, Iakov Zeldovitch showed that for an ellipsoid gas of supergalactic scale, one could resort to an approximation allowing to model that the collapse of matter occurs more quickly according to the small axis, which gives the resulting shape of a crepe ^{[ first ]} .

This approximation assumes that the gaseous ellipsoid is large enough for the effect of pressure to be negligible and that it is enough to consider the gravitational attraction. That is to say that the collapse of the gas is not disturbed by significant external pressure. This assumption is specially valid if the collapse occurred before the cosmological era of the recombination which resulted from the formation of hydrogen atoms ^{[ 2 ]} .

In 1989, Zeldovitch and S. F. Shandarin showed that the initial surpassing of the fluctuation density of random Gaussian fields resulted in a “dense pancake, filaments and a compact agglomerate of matter. »» ^{[ 3 ]} . This model is known as the descending model of galactic formation, in which fragment of supergalactic condensations become protogalaxies ^{[ 4 ]} . The formation of flat concentrations would compress gas by shock waves generated during collapse, by increasing the temperature ^{[ 5 ]} .

At a higher level, the collapse of the largest structures according to the approximation of Zeldovitch is known as “second generation pancakes”, or “supercustes”. At a even higher level, there is a transition to a hierarchical grouping model in which there is a hierarchy of collapse structures. The approximation of truncated Zeldovitch allowed the application of the method to these hierarchical models of cosmological structures, or rising models. This approach truncates the spectrum for the fluctuation of power law with large values ​​of k Before applying the approximation of Zeldovitch ^{[ 6 ]} . We have also shown that Zeldovitch approximation applies in the case of a cosmological constant different from zero ^{[ 7 ]} .

The first example of a Zeldovitch pancake may have been identified in 1991, by the very wide array at the New Mexico ^{[ 8 ] , [ 9 ]} .