Download or read book Magnetorotational Turbulence in Protoplanetary Discs written by Markus Flaig and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk written by Chao-Chin Yang and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In a young protoplanetary disk, planetary objects undergo orbital migration due to the gravitational torques exerted by their surrounding gas. It has been an outstanding issue that an earth-sized planet embedded in a gas-rich environment may rapidly migrate into its host star. In this dissertation, I study some of the processes that affect the orbital migration of planetary objects and their roles on planet formation scenarios. Sharp density features in protoplanetary disks, for instance at the edge of a magnetically dead zone, have recently been proposed as effective barriers to slow down or even stop the problematically fast migration of planetary cores into their central star. Density features on a radial scale approaching the disk vertical scale height might not exist, however, since they could be Rayleigh (or more generally Solberg-Høiland) unstable. Stability must be checked explicitly in one-dimensional viscous accretion disk models because these instabilities are artificially eliminated in the process of reducing the full set of axisymmetric equations. The disk thermodynamics, via the entropy stratification, and its vertical structure also influence stability when sharp density features are present. We propose the concept of Rayleigh adjustment for viscous disk models: any density feature that violates Rayleigh stability (or its generalization) should be diffused radially by hydrodynamical turbulence on a dynamical time-scale, approaching marginal stability in a quasi-continuous manner. Due to the gravitational influence of density fluctuations in the gas disk subject to magneto-rotational instability, planetesimals and protoplanets undergo diffusive radial migration as well as changes of other orbital properties. The magnitude of the effect on particle orbits has important consequences for planet formation scenarios. To accurately measure the gravitational influence of turbulent density fluctuations on particle orbits, numerical simulations capturing both large-scale and small-scale coherent structures are required. Using local shearing boxes with various resolutions up to 64 points per disk scale height and horizontal sizes up to 16 scale heights, we systematically study the corresponding density structure and particle orbit evolution. We consider ideal magnetized disks with isothermal equation of state, and compare disks with and without vertical stratification. We find that although the results converge with resolution for fixed box dimensions, the response of the particles to the gravity of the turbulent gas strongly depends on the horizontal box dimension. Our results indicate the dominance of large-scale density structures, which are closely related to recently discussed zonal flow models of protoplanetary disks. Based on heuristic arguments, some implications may be drawn from the measurements of our local models. The radial diffusive migration of protoplanets induced by magneto-rotational turbulence may be unimportant compared to secular migration. Kilometer-sized planetesimals moving in magneto-rotational turbulence may not suffer from mutual collisional destruction, except for those in the inner region of a young protoplanetary disk. Before these results can be considered valid, though, it will be necessary to elucidate the discrepancies that have appeared between global and local models.
Download or read book Numerical Models of the Early Stages of Planet Formation written by Anders Johansen and published by VDM Publishing. This book was released on 2008 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the earliest stages of planet formation micrometer-sized dust grains collide and gradually build up kilometer-sized planetesimals, bodies that are so large that they can attract each other directly by gravity. This is an important landmark on the way to real planets because of the change to gravity-dominated growth. The road from boulders to planetesimals is however poorly known. Boulders have poor sticking properties and spiral into the young star due to the head wind from the slower rotating gas. This work presents the first detailed computer simulations of the motion of dust and boulders in turbulent protoplanetary discs. The turbulent diffusion coefficient of small dust grains is measured to be surprisingly high, whereas larger boulders concentrate by up to two orders of magnitude in transient high pressure regions that arise spontaneously in magnetorotational turbulence. The coupled motion of boulders and gas is found to be linearly unstable to the so-called streaming instability, leading to a turbulent state that is characterised by dense clumps of boulders that shield each other against the head wind of the gas.
Download or read book Astrophysical Disks written by S. F. Dermott and published by . This book was released on 1992 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: A companion to earlier volumes (497, 536, 596, 617 and 631) of the Annals, this entry in the nonlinear astronomy series has contributions by most of the acknowledged experts in the field. They write on many topics, all of current interest. As several hold strong opposing views, this is a lively, important and timely publication.
Download or read book Cosmic Magnetic Fields IAU S259 written by International Astronomical Union. Symposium and published by Cambridge University Press. This book was released on 2009-06-11 with total page 716 pages. Available in PDF, EPUB and Kindle. Book excerpt: IAU Symposium 259 presents the first interdisciplinary, comprehensive review of the role of cosmic magnetic fields, involving astronomers and physicists from across the community. Offering both theoretical and observational topics ranging from Earth's habitability to the origin of the universe, this is an invaluable summary for researchers and graduate students.
Download or read book Protostars and Planets V written by Bo Reipurth and published by University of Arizona Press. This book was released on 2007 with total page 994 pages. Available in PDF, EPUB and Kindle. Book excerpt: 'Protostars and Planets V' builds on the latest results from recent advances in ground and space-based astronomy and in numerical computing techniques to offer the most detailed and up-to-date picture of star and planet formation - including the formation and early evolution of our own solar system.
Download or read book Multifluid Simulations of the Magnetorotational Instability in Accretion Disks Around Protostars written by Wayne O'Keeffe and published by . This book was released on 2013 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence is believed to be of importance in molecular cloud formation as well as the star formation processes within them, such as accretion of matter onto young stars from the surrounding accretion disk. The kinetic viscosity associated with differentially rotating accretion disks is not believed to be strong enough to account for observed accretion rates. Turbulent motion, driven by the magnetorotational instability (MRI), may provide an anomalous viscosity well in excess of the kinetic viscosity alone leading to enhanced transport of angular momentum, resulting in a higher rate of accretion onto the forming star. We perform large-scale 3D multifluid simulations of a weakly ionised accretion disk and examine the development and saturation of the turbulence driven by the MRI. This numerical study is carried out using the multifluid MHD code HYDRA. An important effect of multifluid MHD is diffusion of the magnetic field. Simulations which isolate ambipolar and Hall diffusion are studied individually and comparisons between these and ideal MHD and full multifluid simulations are presented. The stresses (magnetic and kinetic) and an estimation of the anomalous viscosity are calculated for all models. From this information we can determine how accretion is affected by the multifluid physics in the presence of the MRI.
Download or read book From Protoplanetary Disks to Planet Formation written by Philip J. Armitage and published by Springer. This book was released on 2019-02-02 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: Is the Sun and its planetary system special? How did the Solar system form? Are there similar systems in the Galaxy? How common are habitable planets? What processes take place in the early life of stars and in their surrounding circumstellar disks that could impact whether life emerges or not? This book is based on the lectures by Philip Armitage and Wilhelm Kley presented at 45th Saas-Fee Advanced Course „From Protoplanetary Disks to Planet Formation“ of the Swiss Society for Astrophysics and Astronomy. The first part deals with the physical processes occurring in proto-planetary disks starting with the observational context, structure and evolution of the proto-planetary disk, turbulence and accretion, particle evolution and structure formation. The second part covers planet formation and disk-planet interactions. This includes in detail dust and planetesimal formation, growth to protoplanets, terrestrial planet formation, giant planet formation, migration of planets, multi-planet systems and circumbinary planets. As Saas-Fee advanced course this book offers PhD students an in-depth treatment of the topic enabling them to enter on a research project in the field.
Download or read book Protostars and Planets VI written by Henrik Beuther and published by University of Arizona Press. This book was released on 2014-12-18 with total page 945 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of a conference held in Heidelberg, Germany, July 15-20, 2013.
Download or read book Astrophysics of Planet Formation written by Philip J. Armitage and published by Cambridge University Press. This book was released on 2020-01-30 with total page 345 pages. Available in PDF, EPUB and Kindle. Book excerpt: Concise and self-contained, this textbook gives a graduate-level introduction to the physical processes that shape planetary systems, covering all stages of planet formation. Writing for readers with undergraduate backgrounds in physics, astronomy, and planetary science, Armitage begins with a description of the structure and evolution of protoplanetary disks, moves on to the formation of planetesimals, rocky, and giant planets, and concludes by describing the gravitational and gas dynamical evolution of planetary systems. He provides a self-contained account of the modern theory of planet formation and, for more advanced readers, carefully selected references to the research literature, noting areas where research is ongoing. The second edition has been thoroughly revised to include observational results from NASA's Kepler mission, ALMA observations and the JUNO mission to Jupiter, new theoretical ideas including pebble accretion, and an up-to-date understanding in areas such as disk evolution and planet migration.
Download or read book The Interplay of Gas Dust and Magnetorotational Instability in Magnetized Protoplanetary Disks written by Timmy N. Delage and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Exoplanet Handbook written by Michael Perryman and published by Cambridge University Press. This book was released on 2018-08-30 with total page 973 pages. Available in PDF, EPUB and Kindle. Book excerpt: With the discovery of planets beyond our solar system 25 years ago, exoplanet research has expanded dramatically, with new state-of-the-art ground-based and space-based missions dedicated to their discovery and characterisation. With more than 3,500 exoplanets now known, the complexity of the discovery techniques, observations and physical characterisation have grown exponentially. This Handbook ties all these avenues of research together across a broad range of exoplanet science. Planet formation, exoplanet interiors and atmospheres, and habitability are discussed, providing in-depth coverage of our knowledge to date. Comprehensively updated from the first edition, it includes instrumental and observational developments, in-depth treatment of the new Kepler mission results and hot Jupiter atmospheric studies, and major updates on models of exoplanet formation. With extensive references to the research literature and appendices covering all individual exoplanet discoveries, it is a valuable reference to this exciting field for both incoming and established researchers.
Download or read book Accretion Flows in Astrophysics written by Nikolay Shakura and published by Springer. This book was released on 2018-10-03 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights selected topics of standard and modern theory of accretion onto black holes and magnetized neutron stars. The structure of stationary standard discs and non-stationary viscous processes in accretion discs are discussed to the highest degree of accuracy analytic theory can provide, including relativistic effects in flat and warped discs around black holes. A special chapter is dedicated to a new theory of subsonic settling accretion onto a rotating magnetized neutron star. The book also describes supercritical accretion in quasars and its manifestation in lensing events. Several chapters cover the underlying physics of viscosity in astrophysical discs with some important aspects of turbulent viscosity generation. The book is aimed at specialists as well as graduate students interested in the field of theoretical astrophysics.
Download or read book From Protoplanetary Disks to Planet Formation written by Philip J. Armitage and published by . This book was released on 2019 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: Is the Sun and its planetary system special? How did the Solar system form? Are there similar systems in the Galaxy? How common are habitable planets? What processes take place in the early life of stars and in their surrounding circumstellar disks that could impact whether life emerges or not? This book is based on the lectures by Philip Armitage and Wilhelm Kley presented at 45th Saas-Fee Advanced Course?From Protoplanetary Disks to Planet Formation" of the Swiss Society for Astrophysics and Astronomy. The first part deals with the physical processes occurring in proto-planetary disks starting with the observational context, structure and evolution of the proto-planetary disk, turbulence and accretion, particle evolution and structure formation. The second part covers planet formation and disk-planet interactions. This includes in detail dust and planetesimal formation, growth to protoplanets, terrestrial planet formation, giant planet formation, migration of planets, multi-planet systems and circumbinary planets. As Saas-Fee advanced course this book offers PhD students an in-depth treatment of the topic enabling them to enter on a research project in the field.
Download or read book Modeling Layered Accretion and the Magnetorotational Instability in Protoplanetary Disks written by Michael V. Lesniak III and published by . This book was released on 2012 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the temperature structure of protoplanetary disks (PPDs) is paramount to modeling disk evolution and future planet formation. PPDs around T Tauri stars have two primary heating sources, protostellar irradiation, which depends on the flaring of the disk, and accretional heating as viscous coupling between annuli dissipate energy. I have written a "1.5-D" radiative transfer code to calculate disk temperatures assuming hydrostatic and radiative equilibrium. The model solves for the temperature at all locations simultaneously using Rybicki's method, converges rapidly at high optical depth, and retains full frequency dependence. The likely cause of accretional heating in PPDs is the magnetorotational instability (MRI), which acts where gas ionization is sufficiently high for gas to couple to the magnetic field. This will occur in surface layers of the disk, leaving the interior portions of the disk inactive ("dead zone"). I calculate temperatures in PPDs undergoing such "layered accretion." Since the accretional heating is concentrated far from the midplane, temperatures in the disk's interior are lower than in PPDs modeled with vertically uniform accretion. The method is used to study for the first time disks evolving via the magnetorotational instability, which operates primarily in surface layers. I find that temperatures in layered accretion disks do not significantly differ from those of "passive disks," where no accretional heating exists. Emergent spectra are insensitive to active layer thickness, making it difficult to observationally identify disks undergoing layered vs. uniform accretion. I also calculate the ionization chemistry in PPDs, using an ionization network including multiple charge states of dust grains. Combined with a criterion for the onset of the MRI, I calculate where the MRI can be initiated and the extent of dead zones in PPDs. After accounting for feedback between temperature and active layer thickness, I find the surface density of the actively accreting layers falls rapidly with distance from the protostar, leading to a net outward flow of mass from ~0.1 to 3 AU. The clearing out of the innermost zones is possibly consistent with the observed behavior of recently discovered "transition disks."
Download or read book Saturn in the 21st Century written by Kevin H. Baines and published by Cambridge University Press. This book was released on 2019 with total page 495 pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed overview of Saturn's formation, evolution and structure written by eminent planetary scientists involved in the Cassini Orbiter mission.
Download or read book Issues in Astronomy and Astrophysics 2013 Edition written by and published by ScholarlyEditions. This book was released on 2013-05-01 with total page 1106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Issues in Astronomy and Astrophysics / 2013 Edition is a ScholarlyEditions™ book that delivers timely, authoritative, and comprehensive information about Planetary Science. The editors have built Issues in Astronomy and Astrophysics: 2013 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Planetary Science in this book to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in Astronomy and Astrophysics: 2013 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.
