Early galactic heavy element production - a phenomenological approach

Abstract

The high abundances of heavy elements in early, extremely metal-poor stars is still an unsolved issue in Galactic Chemical Evolution (GCE). Standard approaches, such as mergers of neutron stars, have several difficulties, and several non-merger production channels are under discussion. Here, we suggest that pre-enriched inflow might explain the heavy elements seen in low metallicity stars in the Galaxy. To characterize the conditions of the origin of such a pre-enriched infall, we apply a heavy-element freeze-out approach. We characterize the initial distribution by Lagrange parameters which are nonequilibrium generalizations of temperature and chemical potentials. We then speculate about the origin of such a pre-enriched infall: The required nonequilibrium conditions might be found in cosmological fluctuations in the early Universe, and might be connected to the formation of primordial black holes.

Comments: 14 pages, 4 figures, 2 tables