| Large amounts of dust (∼ 108 M⊙ ) have been observed in quasi-stellar objects at high-redshift ( z > 5), but the origin of such dust is still a mystery. Most dust formation models rely on classical nucleation theory which treats nucleation in conditions of thermodynamic equilibrium. A theory of nucleation based on the kinetic theory is developed here incorporating non-local thermodynamic equilibrium and taking size dependent grain properties into account. The kinetic theory of nucleation, while computationally more expensive than classical nucleation theory, provides an improved methodology for determining nucleation rates of dust grains, and is well suited for predicting dust yields from astronomical sources. In this improved theory, size dependent grain properties, such as grain shape and binding energy, rather than bulk material properties as in classical nucleation theory, are used whenever possible. Additionally, Monte Carlo methods are employed to evolve the size of the grain and to determine its temperature fluctuations due to collisional heating from monomer attachment and carrier gas interactions. The evaporation rate of a grain depends sensitively on its temperature, an effect not considered in classical nucleation theory. An average detachment rate is calculated for each initial grain size, and attachment and detachment rates as a function of grain size are found. Nucleation rates are calculated from the attachment and average detachment rates. Grain sizes and temperatures as a function of time are presented for two sample materials: water and carbon. Nucleation rates for water droplets are found for saturation levels in the range from 6 to 30 and compared to expansion cloud chamber experiment results. Dust mass yields of carbonaceous grains are calculated and compared with previous dust mass predictions for a 20 M⊙ progenitor core-collapse supernova. |
