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Read e-book online Accretion Processes in Star Formation, 2nd Edition PDF

By Lee Hartmann

ISBN-10: 0511465122

ISBN-13: 9780511465123

ISBN-10: 0511552092

ISBN-13: 9780511552090

ISBN-10: 0521531993

ISBN-13: 9780521531993

ISBN-10: 0521825016

ISBN-13: 9780521825016

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The eventual cessation of accretion in many systems may signal the formation of giant planets, which can open up gaps in the disk, accreting material otherwise destined for the central star. 9 A picture of star and planet formation 19 the initial angular momentum will be so small as to permit collapse directly to stellar dimensions, given the large difference in size between a star and its parent gas cloud, it is plausible to suppose that most of the mass initially lands on the disk(s). Disks are engines for the outward transfer of angular momentum, allowing the accretion of mass to the central star.

Infinite sheets and filaments are equilibrium solutions to the equations of motion and thus can satisfy the Jeans assumption. Consider an isothermal thin sheet with a surface mass density ◦ . As shown in Appendix 2, the dispersion relation indicates that surface density perturbations can grow exponentially in time at a rate , where 2 = 2π G ◦k − cs2 k 2 . , there is a minimum wavelength (a “Jeans” length) for gravitational instability. However, there now is a wavenumber with a maximum growth rate, because the growth rate is zero at both kc and k → 0.

6). 2 Turbulence and cloud lifetimes One of the central problems in star formation theory is to understand the origin and nature of turbulence in molecular clouds (see Elmegreen & Scalo 2004 and Scalo & Elmegreen 2004 for general discussions of interstellar medium turbulence). Turbulent motions may either promote star formation by collecting additional mass into limited regions 24 Beginnings: molecular clouds which can then become gravitationally unstable and collapse, or inhibit star formation in principle by providing a “pressure” which resists gravitational collapse.

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Accretion Processes in Star Formation, 2nd Edition (Cambridge Astrophysics) by Lee Hartmann

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