Astrophysics dust formation

Armed with the results of laboratory studies of astrophysical dust processing, we are able to interpret the complex and varied history of dust in protoplanetary disks. This information is complemented by the detailed analysis of the solid material that remains from the earliest epochs of Solar System formation. 

One recent development in astrophysical stochastic processes has been the widespread use of coagulation calculations for both nucleation phenomena and dust formation and processes that relate to the distribution function for masses and mass ratios in forming stellar systems. The use of the coagulation equation for the study of star and stellar system formation in particular has been quite recent and warrants a review. 

However, since we are dealing in this review primarily with problems related to star formation and galactic evolution, we shall ignore the work that has been done on dust formation and nucleation of classical (chemical) systems. These have been extensively reviewed by Abraham,Burton, and Draine and Salpeter for problems of astrophysical interest. We shall only refer to this literature for analogies which may be of some aid in establishing new directions for work on megascopic systems like interstellar clouds. 

Vidali G, Roser JE, Manico G, Pirronello V (2002). In Farid Salama (ed) Investigation of formation of molecular hydrogen on dust grain analogues. NASA Laboratory Astrophysics Workshop, Book of Abstracts of the NASA LAW held in NASA-Ames Research Center, Moffett Field, California, May 1-3, 2002 Wada S, Kaito C, Kimura S, Tokunaga AT (1999) Adv Space Res 24 523 Xianwei S, Jackson B (2002) Surface Sci 496 318... 

The formation of an amorphous solid was first reported in 1935 [132,133]. These authors used the route of depositing warm water vapor on a cold substrate, which freezes in excess free energy by the rapid change in temperature. At substrate temperatures above 160K, the deposit was found to be crystalline ice I, whereas below this temperature, an amorphous solid was obtained. These deposits are referred to as ASW, which is a microporous material that can adsorb gases [134, 135]. In fact, ASW also condenses on interstellar dust particles and is likely the most abundant form of solid water in the universe. Therefore, studies on ASW bear an astrophysical relevance [134, 136]. The microporosity can be reduced greatly by sintering the sample to no more than 120 K. 

Understanding the mechanism for H2 formation from H atoms in space is an old and important problem in astrophysics. It is generally accepted that H atom recombination takes place on interstellar dust particles [105]. The exact composition of these dust particles is not known, but there is spectroscopic evidence that they contain graphitic components, and this has stimulated several electronic structure studies of the H-graphite interaction [86, 89, 106-109]. The recent DFT studies of Sidis and co-workers [108, 109] and Sha and Jackson [89], who modeled graphite as a coronene molecule and a slab, respectively, are in general agreement. We review the results of these studies in Section 3.1. 

Tiny solid cosmic particles - often referred to as dust - are the ultimate source of solids from which rocky planets, planetesimals, moons, and everything on them form. The study of the dust particles genesis and their evolution from interstellar space through protoplanetary disks into forming planetesimals provides us with a bottom-up picture on planet formation. These studies are essential to understand what determines the bulk composition of rocky planets and, ultimately, to decipher the formation history of the Solar System. Dust in many astrophysical settings is readily observable and recent ground- and space-based observations have transformed our understanding on the physics and chemistry of these tiny particles. 

Planet-formation studies uniquely benefit from three disciplines astronomical observations of extrasolar planet-forming disks, analysis of material from the early Solar System, and laboratory astrophysics experiments. Pre-planetary solids, fine dust, and chondritic components are central elements linking these studies. 

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