Description acceptable. In the “cloud-in-cloud” problem, these regions correspond to the outer clouds. In an Einstein-de Sitter universe, a ratio named for these objects is exactly equal to 18 times pi squared at virialization. These regions are perturbations with a “top-hat” shaped profile in the spherical collapse model, which models their growth. The aforementioned ratio named for these objects is symbolized delta and is often rounded to 200 in calculations of virial radius. These regions in the primordial plasma generate (*) baryon acoustic oscillations in the CMB spectrum. These regions are produced by the amplifications of quantum fluctuations by inflation, and therefore serve as the “seeds” of structure formation. For 10 points, name these regions where a quantity equal to mass over volume is greater than that of the universe as a whole. ■END■
ANSWER: overdensities [or overdensity; or overdense regions; accept answers referring to regions of higher (mass) density or regions where the density is greater than that of the universe; anti-prompt on stars, star clusters, globular clusters, open clusters, galaxies, galaxy clusters, dark matter halos, large-scale structure, or giant molecular clouds by asking “which is an example of what more generally defined regions?”; prompt on answers referring to gravitationally bound regions]
<Chen, Other Science>
= Average correct buzz position