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 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 Global Accretion Disk Simulations of Magneto Rotational Instability written by Rainer Arlt and published by . This book was released on 2001 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Role of Magnetic Fields in the Formation of Stars written by Derek Ward-Thompson and published by Frontiers Media SA. This book was released on 2020-06-29 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Theory of Accretion Disks written by F. Meyer and published by Springer. This book was released on 1989-09-30 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the NATO Advanced Research Workshop, Garching, Germany, March 6-10, 1989
Download or read book Gravitoturbulence and Its Interactions with the Magneto Rotational Instability in Accretion Disks written by Lucas Löhnert 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 Outflows and Accretion at the Disk magnetosphere Boundary written by Patrick S. Lii and published by . This book was released on 2015 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accreting magnetized stars are ubiquitous throughout astrophysics and can be found in a variety of astrophysical contexts at both the dawning and closing stages of stellar evolution. These include the young stars at the center of T Tauri-type systems, accreting white dwarfs in cataclysmic variables as well as neutron stars found in low-mass X-ray binaries. The interaction between these stars and their accretion discs is a process which is fundamental to astrophysics: of particular importance is the disc-magnetosphere interaction which determines many of the spectral and time-variable photometric signatures observed in these systems. However, direct imaging of the disc-magnetosphere boundary is observationally challenging due to current resolution limitations while purely analytical studies are difficult due to the highly non-linear nature of magnetohydrodynamic interactions. Simulations bridge the gap between theory and observation and permit us to model the complex interactions in the inner disc with unprecedented detail. In this work, we present the results of pioneering magnetohydrodynamic (MHD) simulations of accretion, planet migration and outflow phenomena at the discmagnetosphere boundary and in the inner disc. In order to investigate these processes, we have developed scalable, high-resolution Godunov-type MHD codes in 2.5D axisymmetric cylindrical, 2D plane polar, and fully 3D cylindrical coordinates aimed at studying accretion driven by the magnetorotational instability as well as the discmagnetosphere interaction. The codes support the inclusion of a planetary perturber and include modules for [alpha]-type viscosity and diffusivity in the disc. Our MHD simulations have established the occurrence of long-lasting outflows in both slowly and rapidly rotating stars. In the slowly rotating regime where rm [LESS-THAN OR EQUAL TO] rc, a well-collimated outflow is launched from the disc-magnetosphere boundary in regimes where the accretion rate is high and the stellar dipole is strongly compressed. The models show that the matter outflows from the disc-magnetosphere boundary with halfopening angles [theta] = 20[-]30? and is collimated by the toroidal magnetic field such that the opening angle narrows to [theta] = 4 [-] 20? at the edge of the simulation region. The outflow velocities range from 30 km s[-]1 at the outer edge of the jet to more than 260 km s[-]1 in the interior regions. This outflow mechanism may help to explain the spectral features observed in the major accretion events associated with FU Orionis and EX Lupi-type outbursts as well as the powerful bipolar jets observed in T Tauri systems. In the rapidly rotating propeller regime of accretion where the magnetosphere rotates faster than the inner disk, the MHD models show the emergence a matter-dominated magnetocentrifugal outflow driven from the disc-magnetosphere boundary. However, unlike the outflow in slower rotating regime, the propeller outflow is primarily rotationpowered and can launch a large majority of the accreting matter into a wide angle propeller wind ([theta] ~ 45?). If the accretion rate exceeds the ejection rate, the accretion onto the star proceeds episodically through a cyclic accumulation-accretion mechanism in which episodes of matter accumulation are followed by a brief episode of simultaneous ejection and accretion onto the star. This cyclic accumulation-accretion mechanism may explain the decahertz flaring observed in some accreting millisecond pulsars expected to be in the propeller regime of accretion. These propeller-driven outflows efficiently transport angular momentum away from the star and may be largely responsible for the rapid spin-down of stars in the propeller regime. While the star-disc interaction is critical for understanding the inner disc dynamics, planet-disc interactions play a dominant role in determining the final period-mass distribution of planets discovered by modern exoplanet surveys. Protoplanetary discs can have large central cavities at the dust sublimation radius or the disc-magnetosphere boundary. Using 2D simulations, Masset et al. 2006 showed that migrating planets which encounter the positive surface density gradient at the disc-cavity boundary may become stably trapped due to the action of the corotation torque. We build on their work and study the disc-planet interaction for planets with initial orbits inside, outside, and coincident with the disc-cavity boundary in both 2D and 3D hydrodynamic simulations. We find that the trapping mechanism persists in the 3D simulations, with migration rates that depend on the surface density profile at the surface density transition. The trapping mechanism is robust and may cause the planet to migrate inward or outward in tandem with the disc-cavity boundary which may move as the young star evolves along the Hayashi track toward the main sequence.
Download or read book Magnetorotational Instability in Protostellar Discs written by Raquel Salmeron and published by . This book was released on 2004 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Self Exciting Fluid Dynamos written by Keith Moffatt and published by Cambridge University Press. This book was released on 2019-04-25 with total page 540 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exploring the origins and evolution of magnetic fields in planets, stars and galaxies, this book gives a basic introduction to magnetohydrodynamics and surveys the observational data, with particular focus on geomagnetism and solar magnetism. Pioneering laboratory experiments that seek to replicate particular aspects of fluid dynamo action are also described. The authors provide a complete treatment of laminar dynamo theory, and of the mean-field electrodynamics that incorporates the effects of random waves and turbulence. Both dynamo theory and its counterpart, the theory of magnetic relaxation, are covered. Topological constraints associated with conservation of magnetic helicity are thoroughly explored and major challenges are addressed in areas such as fast-dynamo theory, accretion-disc dynamo theory and the theory of magnetostrophic turbulence. The book is aimed at graduate-level students in mathematics, physics, Earth sciences and astrophysics, and will be a valuable resource for researchers at all levels.
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 Plasma Physics for Astrophysics written by R. M. Kulsrud and published by Princeton University Press. This book was released on 2005 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: Designed to teach plasma physics and astrophysics 'from the ground up', this textbook proceeds from the simplest examples through a careful derivation of results and encourages the reader to think for themselves.
Download or read book The Undead Zone written by Uditansh Sharma and published by . This book was released on 2022-03-29 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aaditya is a police officer, his brother disappeared from his office three years ago. Now he has some clues about it. He visits the place where he was seen, there an old man told him that he might have gone toward the mountain and that place is dangerous and you should take some weapon with you. He gave Aaditya a Handgun. While he travels toward the mountain he encounters some creature and now just what might be this creature and what will happen next and will he be able to find his brother or if his brother dead. You will find that when you read it. And the writer doesn't want to offend anyone so he has made a fictional country that is related to India and in next addition will be about India and so do follow me.
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 Physical Processes in Circumstellar Disks Around Young Stars written by Paulo J. V. Garcia and published by University of Chicago Press. This book was released on 2011-05-15 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: Circumstellar disks are vast expanses of dust that form around new stars in the earliest stages of their birth. Predicted by astronomers as early as the eighteenth century, they weren’t observed until the late twentieth century, when interstellar imaging technology enabled us to see nascent stars hundreds of light years away. Since then, circumstellar disks have become an area of intense study among astrophysicists, largely because they are thought to be the forerunners of planetary systems like our own—the possible birthplaces of planets. This volume brings together a team of leading experts to distill the most up-to-date knowledge of circumstellar disks into a clear introductory volume. Understanding circumstellar disks requires a broad range of scientific knowledge, including chemical processes, the properties of dust and gases, hydrodynamics and magnetohydrodynamics, radiation transfer, and stellar evolution—all of which are covered in this comprehensive work, which will be indispensable for graduate students, seasoned researchers, or even advanced undergrads setting out on the study of planetary evolution.
Download or read book Cosmic Magnetism written by Percy Seymour and published by CRC Press. This book was released on 1986 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of extraterrestrial magnetic fields is a relatively new one, confirmation of the existance of the first such field (that of our Sun) having come a s late as 1908. In the past 30 years a great ammount of knowledge has been accumulated on Cosmic Magnetism, which has turned out to be a truly fascinating topic for study. Percy Seymour's book is the first to deal with the topic in a non-mathematical way, and he offers a fine introduction to his subject. The first three chapters consolidate our knowledge on magnetism in general and the magnetic field of the Earth, as well as discussing the reasons for studying astronomy and cosmic magnetism in particular. The remainder of the book is devoted to the main areas of cosmic magnetism - solar, plantetary and interplanetary fields, fields in stars and pulsars, fields of the milky way and fields in other galaxies. Cosmic Magnetism in an ideal book for sixth-formers and undergraduates studying physics or astronomy and will also appeal to amateur astronomers. as previous work on this topic has been 'hidden' in specialised academic journals.
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 Interstellar Turbulence written by José Franco and published by Cambridge University Press. This book was released on 1999-05-28 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: This timely volume presents a series of review articles covering every aspect of interstellar turbulence--from accretion disks, molecular clouds, atomic and ionized media, through to spiral galaxies - based on a major international conference held in Mexico City.With advances in observational techniques and the development of more efficient computer codes and faster computers, research in this area has made spectacular progress in recent years. This book provides a comprehensive overview of the most important developments in observing and modelling turbulent flows in the cosmos. It provides graduate student and researchers with a state-of-the-art summary of observational, theoretical and computational research in interstellar turbulence.
