Electron-positron plasma in GRBs and in cosmology

TL;DR

This paper compares electron-positron plasma conditions in the early Universe and GRB sources, highlighting differences in dynamics, nuclear composition, and photon scattering, with implications for understanding cosmology and GRB physics.

Contribution

It provides a detailed analysis of the physical differences and similarities between electron-positron plasmas in cosmological and GRB contexts, emphasizing their dynamical and compositional distinctions.

Findings

Electron-positron plasma in GRBs accelerates thermally, unlike the decelerating early Universe.

Nuclear synthesis in the early Universe differs from element destruction in GRB plasma.

GRB plasma does not cool enough to recombine, unlike the primordial plasma.

Abstract

Electron-positron plasma is believed to play imporant role both in the early Universe and in sources of Gamma-Ray Bursts (GRBs). We focus on analogy and difference between physical conditions of electron-positron plasma in the early Universe and in sources of GRBs. We discuss a) dynamical differences, namely thermal acceleration of the outflow in GRB sources vs cosmological deceleration; b) nuclear composition differences as synthesis of light elements in the early Universe and possible destruction of heavy elements in GRB plasma; c) different physical conditions during last scattering of photons by electrons. Only during the acceleration phase of the optically thick electron-positron plasma comoving observer may find it similar to the early Universe. This similarity breaks down during the coasting phase. Reprocessing of nuclear abundances may likely take place in GRB sources. Heavy nuclear elements are then destroyed, resulting mainly in protons with small admixture of helium. Unlike the primordial plasma which recombines to form neutral hydrogen, and emits the Cosmic Microwave Background Radiation, GRB plasma does not cool down enough to recombine.