The Shape of the First Collapsed Objects
S. F. Shandarin, A. L. Melott, K. McDavitt, J. L. Pauls, J. Tinker
Physical Review Letters
Since the early seventies, there was a conjecture that the first collapse of a selfgravitating dust--like medium (appropriate approximation for nonbaryonic dark matter) results in the formation of a "pancake" object, that is a thin surface. The conjecture has been based on the Zel'dovich approximate solution of the nonlinear gravitational instability of a generic smooth density perturbation. Recent works cast doubt on the Zel'dovich conjecture, suggesting that the first collapse might be
... like or filament--like rather than pancake--like. Our N--body simulations show first pancake collapse. We can reject with 97% confidence the Bayesian prior that the other kinds of collapse are more or equally probable.