Condensation of carbon in radioactive supernova gas

Metallofullerene and fullerene formation from condensing carbon gas under conditions of stellar outflows and implication to stardust

Carbonaceous presolar grains of supernovae origin have long been isolated and are determined to be the carrier of anomalous (22)Ne in ancient meteorites. That exotic (22)Ne is, in fact, the decay isotope of relatively short-lived (22)Na formed by explosive nucleosynthesis, and therefore, a selective and rapid Na physical trapping mechanism must take place during carbon condensation in supernova ejecta. Elucidation of the processes that trap Na and produce large carbon molecules should yield insight into carbon stardust enrichment and formation. Herein, we demonstrate that Na effectively nucleates formation of Na@C60 and other metallofullerenes during carbon condensation under highly energetic conditions in oxygen- and hydrogen-rich environments. Thus, fundamental carbon chemistry that leads to trapping of Na is revealed, and should be directly applicable to gas-phase chemistry involving stellar environments, such as supernova ejecta. The results indicate that, in addition to empty fullerenes, metallofullerenes should be constituents of stellar/circumstellar and interstellar space. In addition, gas-phase reactions of fullerenes with polycyclic aromatic hydrocarbons are investigated to probe "build-up" and formation of carbon stardust, and provide insight into fullerene astrochemistry.

Supernova olivine from cometary dust

An interplanetary dust particle contains a submicrometer crystalline silicate aggregate of probable supernova origin. The grain has a pronounced enrichment in 18O/16O (13 times the solar value) and depletions in 17O/16O (one-third solar) and 29Si/28Si (<0.8 times solar), indicative of formation from a type II supernova. The aggregate contains olivine (forsterite 83) grains <100 nanometers in size, with microstructures that are consistent with minimal thermal alteration. This unusually iron-rich olivine grain could have formed by equilibrium condensation from cooling supernova ejecta if several different nucleosynthetic zones mixed in the proper proportions. The supernova grain is also partially encased in nitrogen-15-rich organic matter that likely formed in a presolar cold molecular cloud.

Testing wave packet dynamics in computing radiative association cross sections

A time-dependent wave packet method is used to compute cross sections for radiative recombination reactions using the Li((2)S)+H(+)-->LiH(+)(X (2)Sigma(+))+gamma as a test case. Cross sections are calculated through standard time-to-energy mapping of the time-dependent transition moment and a useful method is introduced to deal with the low collision energy regime. Results are in quantitative agreement over the whole energy range 10(-4)-5 eV with previous time-independent results for the same system [I. Baccarelli, L. Andric, T. Grozdanov, and R. McCarroll, J. Chem. Phys. 117, 3013 (2002)], thereby suggesting that the method can be of help in computing radiative association cross sections for more complicated systems.

Type II supernovae as a significant source of interstellar dust

Large amounts of dust (>10(8)M(o)) have recently been discovered in high-redshift quasars and galaxies corresponding to a time when the Universe was less than one-tenth of its present age. The stellar winds produced by stars in the late stages of their evolution (on the asymptotic giant branch of the Hertzsprung-Russell diagram) are thought to be the main source of dust in galaxies, but they cannot produce that dust on a short enough timescale (&<1 Gyr) to explain the results in the high-redshift galaxies. Supernova explosions of massive stars (type II) are also a potential source, with models predicting 0.2-4M(o) of dust. As massive stars evolve rapidly, on timescales of a few Myr, these supernovae could be responsible for the high-redshift dust. Observations of supernova remnants in the Milky Way, however, have hitherto revealed only 10(-7)-10(-3)M(o) each, which is insufficient to explain the high-redshift data. Here we report the detection of approximately 2-4M(o) of cold dust in the youngest known Galactic supernova remnant, Cassiopeia A. This observation implies that supernovae are at least as important as stellar winds in producing dust in our Galaxy and would have been the dominant source of dust at high redshifts.

A diamond trilogy: superplumes, supercontinents, and supernovae

Diamond is a remarkable mineral and has been long recognized for its unusual physical and chemical properties: robust and widespread in industry, yet regally adorned. This diversity is even greater than formally appreciated because diamond is recognized as an extraordinary recorder of astrophysical and geodynamic events that extend from the far reaches of space to Earth's deep interior. Many diamonds are natural antiques that formed in presolar supernovae by carbon vapor deposition, in asteroidal impacts and meteorite craters by shock metamorphism, and in Earth's mantle 1 to 2 billion years after planetary accretion from fluids and melts. The carbon in diamond is primordial, but there are unexplained isotopic fractionations and uncertainties in heterogeneity.