The First Compact Objects in the $\Lambda$-dominated Universe

Abstract

We calculate the evolution of a low-mass ($M \le 10^5 M_{\odot}$) spherically symmetric density perturbation in the $\Omega_b h^2=0.02$, $\Omega_M =0.35$, $\Omega_{\Lambda}=0.65$, $h=0.72$ Universe. The results are compared with the ones that assume no cosmological constant and the flat, dark matter dominated Universe. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that direct formation of bound objects with such masses by $z=8$ is unlikely so in fact they may form only through fragmentation of greater objects. This is in stark contrast to the $\Omega=1$ pure CDM cosmology, where low-mass objects form abundantly at redshits $z>10$.