Chemical Energy in Cold-Cloud Aggregated: The Origin of Meteoritic Chondrules

If interstellar particles and molecules accumulate into larger particles during the collapse of a cold cloud, the resulting aggregates contain a large store of internal chemical energy. It is here proposed that subsequent warming of these accumulates leads to a thermal runaway when exothermic chemical reactions begin within the aggregate. These, after cooling, are the crystalline chondrules found so abundantly within chondritic meteorites. Chemical energy can also heat meteoritic parent bodies of any size, and both thermal metamorphism and certain molten meteorites are proposed to have occurred in this way. If this new theory is correct, (1) the model of chemical condensation in a hot gaseous solar system is eliminated, and (2) a new way of studying the chemical evolution of the interstellar medium has been found. A simple dust experiment on a comet flyby is proposed to test some features of this controversy

Analytic Approximation of Carbon Condensation Issues in Type II Supernovae

I present analytic approximations for some issues related to condensation of graphite, TiC, and silicon carbide in oxygen-rich cores of supernovae of Type II. Increased understanding, which mathematical analysis can support, renders researchers more receptive to condensation in O-rich supernova gases. Taking SN 1987A as typical, my first analysis shows why the abundance of CO molecules reaches an early maximum in which free carbon remains more abundant than CO. This analysis clarifies why O-rich gas cannot oxidize C if 56Co radioactivity is as strong as in SN 1987A. My next analysis shows that the CO abundance could be regarded as being in chemical equilibrium if the CO molecule is given an effective binding energy rather than its laboratory dissociation energy. The effective binding energy makes the thermal dissociation rate of CO equal to its radioactive dissociation rate. This preserves possible relevance for the concept of chemical equilibrium. My next analysis shows that the observed abundances of CO and SiO molecules in SN 1987A rule out frequent suggestions that equilibrium condensation of SUNOCONs has occurred following atomic mixing of the He-burning shell with more central zones in such a way as to reproduce roughly the observed spectrum of isotopes in SUNOCONs while preserving C/O \u3e 1. He atoms admixed along with the excess carbon would destroy CO and SiO molecules, leaving their observed abundances unexplained. The final analysis argues that a chemical quasiequilibrium among grains (but not gas) may exist approximately during condensation, so that its computational use is partially justified as a guide to which mineral phases would be stable against reactions with gas. I illustrate this point with quasiequilibrium calculations by Ebel & Grossman that have shown that graphite is stable even when O/C \u3e1 if prominent molecules are justifiably excluded from the calculation of chemical equilibrium

Galactic Chemical Evolution and Nucleocosmochronology: Analytic Quadratic Models

The author presents a new analytic model of the chemical evolution of the galaxy. Explicit solutions for a gas mass, star mass, metallicity, and radiochronometers are obtained for models with parametrized galactic infall, and for which the star formation rate is proportional to the gas mass. Because all physically interesting observables have a simple explicit dependence on the parameters which themselves map a wide space of physical possibilites, the author suggests adopting this model as a reference standard for studies of chemical evolution

A Presolar Galactic Merger Spawned the Sic-Grain Mainstream

The merger of a metal-poor satellite galaxy with the Milky Way about 5–6 Gyr ago is postulated to resolve three great unexplained conflicts presented by mainstream presolar stardust SiC grains. The model allows all of the asymptotic giant branch (AGB) carbon stars that donated these grains to have been formed nearly simultaneously in a starburst generated by gaseous mixing, despite their great apparent age differences when evaluated in terms of Galactic chemical evolution (GCE). The model explains why a precisely measured lin-ear correlation exists between the ratios 29Si/28Si and 30Si/28Si in the initial compositions of those AGB stars. It suggests why the slope of that normalized correlation line is m ¼ 4=3 rather than unity, as predicted by GCE. It also suggests why the solar silicon isotopes lie near the bottom of that mainstream correlation line rather than near its top, as expected by current astrophysical ideas. By addressing many isotopic puzzles found within the solar composition, the model also yields a fresh view of the origin of the Sun and of its relationship to the Galaxy. The model is remarkable in reading dynamic events of the presolar history of the Milky Way from precise isotopic ratios measured in terrestrial laboratories within individual micron-sized presolar grains that have been extracted from meteorites that formed 4.56 Gyr ago but that fell only recently to Earth

Condensation of Carbon in Supernovae: Graphite in Meteorites

A new model for the carbon condensation chemistry within supernovae has been developed (1) showing that carbon condensates will occur even in gas having abundance ratio O/C \u3e1. The escape from thermochemical bondage of C within CO occurs because the supernova radioactivity dissociates the CO molecule (2). We consider several immediate astrophysical consequences

Nuclear Cosmochronology within Analytic Models of the Chemical Evolution of the Solar Neighborhood

This paper investigates whether the age of the Galaxy can be deduced from natural radioactivity. I demonstrate that two recent influential claims (by Butcher and by Fowler) that such observations set the age at TG = 10 Gyr depend on special assumptions that run counter to existing astrophysical theory, so that greater ages are possible. I derive exact analytic time-dependent linear models of the chemical evolution of the solar neighbourhood to illustrate the extent to which continuous growth of the local mass density by eaily additions of metal-poor matter greatly lengthens the galactic ages inferred from the Solar System abundances of natural radioactive nuclei and of their stable daughters. I argue that such time-dependent infall of local matter is plausible and supported by several arguments, and I demonstrate that its past magnitude is the greatest uncertainty in nuclear cosmochronology, which I argue at length to be now the province more of the astronomer than of the nuclear physicist. I attempt here to enlarge the scientific community of these concerns by a very detailed treatment that makes explicit the dependence of age on the parameters describing the infall. In addition to these general aims I present many specific new results, especially: (i) new exact analytic models of chemical evolution; (ii) analysis of the five cosmoradiogenic chronologies (Clayton) in addition to the three based on U and Th; (iii) useful expressions for exact analytic secondary metallicity showing that the magnitude of the secondary component of s-process nucleosynthesis influences the Th/Nd observations in G-dwarfs more than galactic age does; (iv) a new argument in stellar evolution based on the 13C neutron source that may finally resolve the old puzzle of apparent contemporaneous growth of r-process and s-proccss abundances, an argument that would if correct lend support to Butcher\u27s extreme assumption of equal growth rates; (v) an explicit derivation of the distinction between the rate of growth of local metallicity in the gas and the age spectrum of its imbedded nuclei. An unbiased look at all eight methods together favours a galactic age 1

Line 57Co Gamma Rays: New Diagnostic of Supernova Structure

The nuclear gamma-ray lines emitted when 57Co decays to 57Fe should be detectable for several years following Galactic supernovae, and the time structure of their intensity relative to those emitted following the 56Ni and 56Co decays can reveal the structure of the exploding star. An analysis of a simplified analytic model is presented as an example

A Walking Tour of Residential Seneca

In 1870, Seneca was a wilderness area on the Blue Ridge Railroad Line. When the Richmond Air Line Railroad also crossed at this spot, men saw the opportunity to develop a town at their intersection. They purchased the necessary land and marked the lots. The first auction was held in August 1873. The town that developed was called Seneca City, named for a tribe of Indians that lived nearby. —Donald D. Clayton, from the Introductionhttps://tigerprints.clemson.edu/cudp_regional/1004/thumbnail.jp