QUARK-NOVAE, COSMIC REIONIZATION, AND EARLY r-PROCESS ELEMENT PRODUCTION

We examine the case for quark-novae (QNe) as possible sources for the reionization and early metal enrichment of the universe. QNe are predicted to arise from the explosive collapse (and conversion) of sufficiently massive neutron stars into quark stars (QSs). A QN can occur over a range of timescales following the supernova (SN) event. For QNe that arise days to weeks after the SNe, we show that dual shock that arises as the QN ejecta encounter the SN ejecta can produce enough photons to reionize hydrogen in most of the intergalactic medium (IGM) by z ∼ 6. Such events can explain the large optical depth τe ∼ 0.1 as measured by WMAP, if the clumping factor, C, of the material being ionized is smaller than 10. We suggest a way in which a normal initial mass function for the oldest stars can be reconciled with a large optical depth as well as the mean metallicity of the early IGM post reionization. We find that QN also make a contribution to r-process element abundances for atomic numbers A ⩾ 130. We predict that the main cosmological signatures of QNe are the gamma-ray bursts that announce their birth. These will be clustered at redshifts in the range z ∼ 7–8 in our model.