Ambipolar Diffusion, Interstellar Dust, and the Formation of Cloud Cores and Protostars. I. Basic Physics and Formulation of the Problem

1993 ◽  
Vol 418 ◽  
pp. 774 ◽  
Author(s):  
Glenn E. Ciolek ◽  
Telemachos Ch. Mouschovias
Keyword(s):  
Interstellar Dust ◽  
Ambipolar Diffusion ◽  
Basic Physics ◽  
Cloud Cores

scholarly journals Desorption of N2, CO, CH4, and CO2 from interstellar carbonaceous dust analogues

2019 ◽  
Vol 490 (2) ◽  
pp. 2936-2947
Author(s):  
B Maté ◽  
M Jimenez-Redondo ◽  
R J Peláez ◽  
I Tanarro ◽  
V J Herrero
Keyword(s):  
Interstellar Dust ◽  
Model Simulation ◽  
Amorphous Solid ◽  
Desorption Energy ◽  
Wigner Equation ◽  
Energy Distributions ◽  
Zero Order Kinetics ◽  
Cloud Cores ◽  
Hydrogenated Amorphous ◽  
Monolayer Coverage

ABSTRACT The interaction of volatile species with carbonaceous interstellar dust analogues is of relevance in the chemistry and physics of dense clouds in the interstellar medium. Two deposits of hydrogenated amorphous carbon (HAC), with different morphologies and aromatic versus aliphatic ratio in their structure, have been grown to model interstellar dust. The interaction of N2, CO, CH4, and CO2 with these two surfaces has been investigated using thermal programmed desorption (TPD). Desorption energy distributions were obtained by analysing TPD spectra for one monolayer coverage with the Polanyi–Wigner equation. The desorption energies found in this work for N2, CO, and CH4 are larger by 10–20 per cent than those reported in the literature for siliceous or amorphous solid water surfaces. Moreover, the experiments suggest that the interaction of the volatiles with the aromatic substructure of HAC is stronger than that with the aliphatic part. Desorption of CO2 from the HAC surfaces follows zero-order kinetics, reflecting the predominance of CO2–CO2 interactions. A model simulation of the heating of cold cloud cores shows that the volatiles considered in this work would desorb sequentially from carbonaceous dust surfaces with desorption times ranging from hundreds to tens of thousands of years, depending on the molecule and on the mass of the core.

scholarly journals Molecular Cloud Cores and Protostars: Offsprings of Gravity and Cosmic Magnetism

1990 ◽  
Vol 140 ◽  
pp. 269-279
Author(s):  
Telemachos Ch. Mouschovias
Keyword(s):  
Magnetic Fields ◽  
Time Scales ◽  
Theoretical Calculations ◽  
Mass Function ◽  
Ambipolar Diffusion ◽  
Gravity And Magnetic ◽  
Cloud Cores ◽  
The Magnetic Field

The formation of cloud cores (or fragments) and their evolution into protostars are the inevitable outcome of the struggle between gravity and magnetic fields, with ambipolar diffusion as the agent employed to weaken gravity's fierce opponent. The very specific and crucial role of magnetic fields in star formation deduced from detailed quantitative calculations is summarized. Criteria for collapse against magnetic and thermal-pressure forces are given. Magnetic braking time scales for both aligned and perpendicular rotators, and ambipolar diffusion time scales in both quasistatically and dynamically contracting cores are presented, and their implications are discussed. The possible role of magnetic fields in the determination of the initial (stellar) mass function (IMF) is beginning to emerge. New calculations on the axisymmetric collapse of clouds due to ambipolar diffusion reveal that the relation Bc ∞ ρc1/2 between the magnetic field strength and the gas density in typical cloud cores holds even in the presence of ambipolar diffusion up to densities ~ 109 cm−3. Small masses, high densities, and strong fields observed in H2O masers are consistent with theoretical calculations.

scholarly journals Filament Fragmentation

2001 ◽  
Vol 200 ◽  
pp. 391-400 ◽  
Author(s):  
Shu-ichiro Inutsuka ◽  
Toru Tsuribe
Keyword(s):  
Molecular Clouds ◽  
Mass Function ◽  
Mass Scale ◽  
Thermal Processes ◽  
Dense Cores ◽  
Dense Molecular Cloud ◽  
Basic Physics ◽  
Formation And Evolution ◽  
Field Lines ◽  
Cloud Cores

The formation and evolution processes of magnetized filamentary molecular clouds are investigated in detail by linear stability analyses and non-linear numerical calculations. A one-dimensionally compressed self-gravitating sheet-like cloud breaks up into filamentary clouds. The directions of the longitudinal axes of the resulting filaments are perpendicular to the directions of magnetic field lines unless the column density of the sheet is very small. These magnetized filaments tend to collapse radially without characteristic density, length, and mass scale for the further fragmentation during the isothermal phase. The characteristic minimum mass for the final fragmentation is obtained by the investigation of thermal processes. The essential points of the above processes are analytically explained in terms of the basic physics. A theory for the expected mass function of dense molecular cloud cores is obtained. The expected mean surface density of companions of dense cores is also discussed.

Planetesimal formation in the solar nebula

1999 ◽  
Vol 173 ◽  
pp. 17-30
Author(s):  
T.V. Ruzmaikina
Keyword(s):  
Interstellar Dust ◽  
Solar Nebula ◽  
Kuiper Belt ◽  
Asteroid Belt ◽  
Dust Grains ◽  
Small Bodies ◽  
Interstellar Dust Grains ◽  
Formation And Evolution ◽  
Cloud Cores ◽  
Solid Bodies

AbstractTerrestrial planets, cores of giant planets and small bodies of the solar system − comets and asteroids − resulted from the coagulation of interstellar dust grains, and grains which were melted or evaporated and condensed again in the solar nebula.The paper describes the growth and processing of dust grains and their aggregates, starting from molecular cloud cores through the formation and evolution of the solar nebula and the accumulation of these aggregates in larger solid bodies − planetesimals. Discussed are the processes which could be responsible for the interruption of accumulation in the region of the asteroid belt, and processes which shaped the Kuiper belt.

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