Main stages of evolution of matter in the universe. II

Abstract

A possible scenario for the evolution of the universe following the big bang at t > 10^-5 sec is considered. The necessary conditions that must be present for the formation of stars and stellar systems to be possible are formulated. As a condition for the formation of stars we take kT_s≤ GM_sm_p(3R), and for stellar systems HR ≲ (GM/R)^1/2, where T_s is the temperature of the cosmic plasma, m_p is the mass of a proton, M_s is the mass of a star, M is the mass of a stellar cluster, R is the radius of these celestial bodies, and H is the bubble parameter for the corresponding time. In accordance with these criteria, we assume that in the course of cosmological expansion, neutron stars should have been formed first (times 2.10^-4 ≲ t ≲ 1 sec, densities 0.07 ≲ ρ_B≲ 2.10⁴ g/cm³) and then, in chronological order, appeared white dwarfs (t ≈ 10² sec, ρ_B ≲ 5.10^-3 g/cm³), ordinary stars (t ≈ 4.10⁶ sec, ≲_B ≈ 10^-11 g/cm³), galactic nuclei (t ≈ 3.10¹¹ sec, ≲_B ≈ 5.10^-19 g/cm³, globular clusters (t ≈ 10¹³ sec, ≲_B ≈ 4.10^-21 g/cm³), and galaxies (t ≈ 10¹⁵ sec, ≲_B ≈ 10^-24 g/cm³), where ≲_B is the average density of ordinary (baryon) matter in the universe. It is shown that a galactic nucleus is a stellar system in statistical equilibrium and consists mainly of neutron stars and white dwarfs. The formation of some pulsars (neutron stars with angular rotation rates 1 < Ω < 200 sec^-1) may occur in a galactic nucleus. Observed pulsars should therefore contain some fraction of neutron stars from the nucleus of the Galaxy that were able to escape it over the relaxation time (the tail of the Maxwell distribution, with star velocities v > v₀, where v₀ is the velocity corresponding to the work function 2GMM_s/R, M being the mass and R the radius of the Galaxy’s nucleus.