The first compact objects in the MOND model

Abstract

We trace the evolution of a spherically symmetric density perturbation in the MOdified Newtonian Dynamics (MOND) model. The background cosmological model is a $\Lambda$-dominated, low-${\Omega }_b$ Friedmann model with no Cold Dark Matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that the first density perturbations which collapse to form luminous objects have mass $\sim 10^5{M}_{\odot }$. The time of the final collapse of these objects depends mainly on the value of the MOND acceleration $a_0$ and also on the baryon density ${\Omega }_b$. For the "standard" value $a_0=1.2\times 10^{-8}$ cm/s${}^2$ the collapse starts at redshift $z\sim 160$ for ${\Omega }_b=0.05$ and $z\sim 110$ for ${\Omega }_b=0.02$.

12 pages, 7 figures, talk presented at the XXV School of Theoretical Physics, Ustron, Poland, 9-16 Sept. 2001, to appear in Acta Physica Polonica B