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Register a new userUsing failed supernovae to constrain the Galactic r-process element production
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Rapid neutron capture process (r-process) elements have been detected in a large fraction of metal-poor halo stars, with abundances relative to iron (Fe) that vary by over two orders of magnitude. This scatter is reduced to less than a factor of 3 in younger Galactic disc stars. The large scatter of r-process elements in the early Galaxy suggests that the r-process is made by rare events, like compact binary mergers and rare sub-classes of supernovae. Although being rare, neutron star mergers alone have difficulties to explain the observed enhancement of r-process elements in the lowest metallicity stars compared to Fe. The supernovae producing the two neutron stars already provide a substantial Fe abundance where the r-process ejecta from the merger would be injected. In this work we investigate another complementary scenario, where the r-process occurs in neutron star-black hole mergers in addition to neutron star mergers. Neutron star-black hole mergers would eject similar amounts of r-process matter as neutron star mergers, but only the neutron star progenitor would have produced Fe. Furthermore, a reduced efficiency of Fe production from single stars significantly alters the age-metallicity relation, which shifts the onset of r-process production to lower metallicities. We use the high-resolution [(20 pc)3/cell] inhomogeneous chemical evolution tool `ICE to study the outcomes of these effects. In our simulations, an adequate combination of neutron star mergers and neutron star-black hole mergers qualitatively reproduces the observed r-process abundances in the Galaxy.
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We examine the case for Quark-Novae (QNe) as possible sources for the reionization and early metal enrichment of the universe. Quark-Novae are predicted to arise from the explosive collapse (and conversion) of sufficiently massive neutron stars into quark stars. A Quark-Nova (QN) can occur over a range of time scales following the supernova event. For QNe that arise days to weeks after the supernovae, we show that dual-shock that arises as the QN ejecta encounter the supernova ejecta can produce enough photons to reionize hydrogen in most of the Inter-Galactic medium (IGM) by z ~ 6. Such events can explain the large optical depth tau_e ~ 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 (IMF) 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 Quark-Novae are the gamma-ray bursts that announce their birth. These will be clustered at redshifts in the range z ~ 7-8 in our model.
Long-lived radioactive nuclei play an important role as nucleo-cosmochronometers and as cosmic tracers of nucleosynthetic source activity. In particular nuclei in the actinide region like thorium, uranium, and plutonium can testify to the enrichment of an environment by the still enigmatic astrophysical sources that are responsible for the production of neutron-rich nuclei by the rapid neutron-capture process (r-process). Supernovae and merging neutron-star (NS) or NS-black hole binaries are considered as most likely sources of the r-nuclei. But arguments in favour of one or the other or both are indirect and make use of assumptions; they are based on theoretical models with remaining simplifications and shortcomings. An unambiguous observational determination of a production event is still missing. In order to facilitate searches in this direction, e.g. by looking for radioactive tracers in stellar envelopes, the interstellar medium or terrestrial reservoirs, we provide improved theoretical estimates and corresponding uncertainty ranges for the actinide production ($^{232}$Th, $^{235,236,238}$U, $^{237}$Np, $^{244}$Pu, and $^{247}$Cm) in neutrino-driven winds of core-collapse supernovae. Since state-of-the-art supernova models do not yield r-process viable conditions ---but still lack, for example, the effects of strong magnetic fields--- we base our investigation on a simple analytical, Newtonian, adiabatic and steady-state wind model and consider the superposition of a large number of contributing components, whose nucleosynthesis-relevant parameters (mass weight, entropy, expansion time scale, and neutron excess) are constrained by the assumption that the integrated wind nucleosynthesis closely reproduces the solar system distribution of r-process elements. We also test the influence of uncertain nuclear physics.
We study the evolution of rapid neutron-capture process (r-process) isotopes in the Galaxy. We analyze relative contributions from core collapse supernovae (CCSNe), neutron star mergers (NSMs) and collapsars under a range of astrophysical conditions and nuclear input data. Although the r-process in each of these sites can lead to similar (or differing) isotopic abundances, our simulations reveal that the early contribution of r-process material to the Galaxy was dominated by CCSNe and collapsar r-process nucleosynthesis, while the NSM contribution is unavoidably delayed even under the assumption of the shortest possible minimum merger time.
In this analysis we illustrate how the relatively new emission mechanism known as spinning dust can be used to characterize dust grains in the interstellar medium. We demonstrate this by using spinning dust emission observations to constrain the abundance of very small dust grains (a $lesssim$ 10nm) in a sample of Galactic cold cores. Using the physical properties of the cores in our sample as inputs to a spinning dust model, we predict the expected level of emission at a wavelength of 1cm for four different very small dust grain abundances, which we constrain by comparing to 1cm CARMA observations. For all of our cores we find a depletion of very small grains, which we suggest is due to the process of grain growth. This work represents the first time that spinning dust emission has been used to constrain the physical properties of interstellar dust grains.
We propose a statistical method for decomposition of contributions to iron production from various sources: supernovae Type II and the subpopulations of supernovae Type Ia -- prompt (their progenitors are short-lived stars of ages less then $sim$100 Myr) and tardy (whose progenitors are long-lived stars of ages $>$100 Myr). To do that, we develop a theory of oxygen and iron synthesis which takes into account the influence of spiral arms on amount of the above elements synthesized by both the supernovae Type II and prompt supernovae Ia. We solve this task without of any preliminary suppositions about the ratio among the portions of iron synthesized by the above sources. The relative portion of iron synthesized by tardy supernovae Ia for the life-time of the Galaxy is $sim$35 per cent (in the present ISM this portion is $sim$50 per cent). Correspondingly, the total portion of iron supplied to the disc by supernovae Type II and prompt supernovae Ia is $sim$65 per cent (in the present ISM this portion is $sim$50 per cent). The above result slightly depends on the adopted mass of oxygen and iron synthesized during one explosion of supernovae and the shape (bimodal or smooth) of the so-called Delay Time Distribution function. The portions of iron mass distributed between the short-lived supernovae are usually as follows: depending on the ejected masses of oxygen or iron during one supernovae Type II event the relative portion of iron, supplied to the Galactic disc for its age, varies in the range 12 - 32 per cent (in the present ISM 9-25 per cent); the portion supplied by prompt supernovae Ia to the Galactic disc is 33 - 53 per cent (in ISM 26 - 42 per cent).
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