Type I supernovae and iron nucleosynthesis in the universe

Abstract

It is argued that the iron nucleosynthesis rate in the universe due to SNI outbursts is dependent on the mass function of star formation. Since the mass function depends on the chemical composition and since the masses of SNI precursors have upper limits, the iron nucleosynthesis rate was low at an earlier evolutionary epoch of the universe when mainly massive stars were formed. The iron nucleosynthesis rate should reach a maximum near z ∼ 0.5. At such or similar value of z the well-known ‘step’ in the cosmic γ-ray background spectrum may be explained by the presence of γ-gray quanta accompanying the radioactive⁵⁶Co →⁵⁶Fe decay. An argument is presented against the identification of the hidden mass of the universe with black-hole remnants of ‘type III’ stars.