Protostars

Gehrels, T. (1978), Protostars and Planets, University of Arizona Press, Tucson, pp. 1-756. 

The formation of stars in the interiors of dense interstellar clouds affects the chemistry of the immediate environment in a variety of ways depending on many factors such as the stage in the evolution of star formation, the mass of the star or protostar, and the density and temperature of the surrounding material. In general, the dynamics of the material in the vicinity of a newly forming star are complex and show many manifestations. Table 3 contains a list of some of the better studied such manifestations, which tend to have distinctive chemistries. These are discussed individually below. 

Figure 4.1 A protostar. (Reproduced from Ligure 14.13 "Astronomony, the Evolving Universe" 9th Edition, 2002, by permission of Boris Starosta and Michael Zeilik)...

At 2000 K there is sufficient energy to make the H2 molecules dissociate, breaking the chemical bond the core density is of order 1026 m-3 and the total diameter of the star is of order 200 AU or about the size of the entire solar system. The temperature rise increases the molecular dissociation, promoting electrons within the hydrogen atoms until ionisation occurs. Finally, at 106 K the bare protons are colliding with sufficient energy to induce nuclear fusion processes and the protostar develops a solar wind. The solar wind constitutes outbursts of material that shake off the dust jacket and the star begins to shine. 

Big Bang nucleosynthesis produced only H and He atoms with a little Li, from which nuclei the first generation of stars must have formed. Large clouds of H and He when above the Jeans Mass condensed under the influence of gravitational attraction until they reached the temperatures and densities required for a protostar to form, as outlined. Nuclear fusion powers the luminosity of the star and also results in the formation of heavier atomic nuclei. 

Low (<1 solar mass) Middle (5-10 solar masses) High (>20 solar masses) Protostar — pre-main sequence — main sequence — red giant — planetary nebula — white dwarf — black dwarf Protostar - main sequence — red giant — planetary nebula or supernova —> white dwarf or neutron star Protostar — main sequence —> supergiant — supernova — neutron star... 

The birth of a protostar and its life as a pre-main-sequence star, its descent to the main sequence and death, starting with a red giant leading to planetary nebula and ending in white and black dwarfs. This sequence varies with mass... 

During the temperature rise in protostar formation, molecular dissociation occurs followed by ionisation of atoms. Assume that molecules and atoms are in thermal equilibrium with the protostar ... 

Consider a kinetic model for the formation of H2+ towards the protostar GL2136. A simple model for the hydrogen chemistry of the cloud can be seen with the reaction scheme below ... 

Protostar A star early in the evolutionary process, shortly after the initial gravitational collapse. 

Young stellar object (YSO) Young stellar object - a protostar that is beginning to shine but at low temperature so it has a spectrum with a maximum in the infrared. 

Gibb E. F. et al. (2000). An Inventory of Interstellar Ices toward the Protostar W33A1, Astrophysical Journal, 536 347-356. 

Ott U (1993) Physical and isotopic properties of surviving interstellar carbon phases. In Protostars Planets III. Levy Hand Lunine JI (eds) University of Arizona Press, Tucson, p 883-902 Ott U (1996) Interstellar diamond xenon and timescales of supernova ejecta. Astrophys J 463 344-348 Ott U, Begemann F, Yang J, Epstein S (1988) S-process krypton of variable isotopic composition in the Murchison meteorite. Nature 332 700-702... 

Protein biomolecules consisting of polypeptide chain with large molecular mass Protostar early stage in the formation of a star when gases and dust start to contract due to gravitational forces P-V Work work associated with the expansion or compression of a gas Pyrethroids synthetic forms of pyrethrins, insecticides based on extracts from chrysanthemums... 

Images of a bipolar jet from a protostar taken by the Hubble space telescope. Evolution of the jet with time is visible between the three images. 

The nuclear reaction that finally stabilizes the structure of the protostar is the fusion of two protons to form a deuterium atom, a positron, and a neutrino (1 H(p,p+v)2D). This reaction becomes important at a temperature of a few million degrees. The newly produced deuterium then bums to 3He, which in turn bums to 4He in the proton-proton chain. The proton-proton chain is the main source of nuclear energy in the Sun. With the initiation of hydrogen burning... 

Artistic rendering of four observed stages of star formation, (a) Class 0 object a deeply embedded hydrostatic core surrounded by a dense accretion disk. Strong bipolar jets remove angular momentum, (b) Class I object protostar in the later part of the main accretion phase, (c) Class II object or T Tauri star pre-main-sequence star with optically thick protoplanetary disk, (d) Class III object or naked T Tauri star star has an optically thin disk and thus can be directly observed. Some may have planets. 

Prinn, R. G. (1993) Chemistry and evolution of gaseous circumstellar disks. In Protostars and Planets III, eds. Levy, E. H. and Lunine, J. I. Tucson University of Arizona Press, pp. 1005-1028. 

Hayashi, C., Nakazawa, K., Nakagawa, Y. (1993) Flanetary accretion in the solar gravitational field. In Protostars Planets III, E. H. Levy J. T. Lunine, Eds., pp. 1089-107. Tucson University of Arizona Fress. 

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