We study the velocity distribution in spherical collapses and cluster-pair collisions by use of N -body simulations. Reflecting the violent gravitational processes, the velocity distribution of the resultant quasistationary state generally becomes non-Gaussian. Through the strong mixing of the violent process, there appears a universal non-Gaussian velocity distribution, which is a democratic (...

We show that the behaviour of the outgoing radial null geodesic congruence on the boundary of the trapped region (suitably defined as a four dimensional region) is related to the property of nakedness in spherical dust collapse. The argument involves a conformal transformation which justifies the difference in the Penrose diagrams in the naked and covered dust collapse scenarios.

X iv :g rqc /0 30 80 37 v1 1 2 A ug 2 00 3 Role of Initial Data in Higher Dimensional Quasi-Spherical Gravitational Collapse Ujjal Debnath and Subenoy Chakraborty Department of Mathematics, Jadavpur University, Calcutta-32, India. (Dated: February 7, 2008) We study the gravitational collapse in (n+2)-D quasi-spherical Szekeres space-time (which possess no killing vectors) with dust as the matte...

We investigate the joint density-velocity evolution in $f(R)$ gravity using smooth, compensated spherical top-hats as a proxy for non-linear regime. Using Hu-Sawicki model working example, we solve coupled continuity, Euler and Einstein equations an iterative hybrid Lagrangian-Eulerian scheme. The novel aspect of this scheme is that metric potentials are solved analytically Eulerian frame. assu...

We generalize the spherical collapse model for the formation of bound objects to apply in a Universe with arbitrary positive cosmological constant. We calculate the critical condition for collapse of an overdense region and give exact values of the characteristic densities and redshifts of its evolution.

We show that the behaviour of the outgoing radial null geodesic congruence on the apparent horizon is related to the property of nakedness in spherical dust collapse justifying the difference in the Penrose diagrams in the naked and covered dust collapse scenarios. We provide arguments suggesting that the relationship could be generally valid. [email protected]