Download or read book Morphology Fragmentation and Dynamic Balance an Investigation Into Early Stages of Structure Formation in Molecular Clouds written by Shashwata Ganguly and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Observational Studies of Fragmentation in Molecular Clouds written by Riwaj Pokhrel and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, I explore fragmentation physics in multiple scales in nearby molecular clouds and discuss some implications of fragmentation for cloud structure formation and star formation, primarily by analyzing multi-wavelength observations of dust emission. First, I tested the complete thermal and combined thermal and nonthermal support mechanisms that balance gravitational contraction at multiple scales in the Perseus molecular cloud. I found that the observed multiscale structures in Perseus are consistent with an inefficient thermal Jeans fragmentation, where the Jeans efficiency increases from the largest scale ($\gtrsim$10s of pc) to the smallest scale ($\sim$10s of AU). Next, I studied the effect of the formation of dense self-gravitating structures and star formation on the gas distribution in terms of its column density distribution function (N-PDF). I found that the evolutionary effect of clouds has corresponding changes on the N-PDF functional form, with a lognormal shape in diffuse regions that have negligible star formation, a lognormal and two power-laws in denser regions with moderate star formation, and a lognormal and one power-law in the densest regions with highly efficient clustered star formation. Finally, I explored the variations of star and gas surface densities in twelve molecular clouds using various techniques. I found that the stellar mass surface density of the recently formed stars varies as the square of the gas mass surface density in all twelve clouds. Also, I do not find any evidence of a column density threshold for efficient star formation.
Download or read book Literature 1991 Part 2 written by Astronomisches Rechen-Institut and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 1592 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Astronomy and Astrophysics Abstracts" appearing twice a year has become oneof the fundamental publications in the fields of astronomy, astrophysics andneighbouring sciences. It is the most important English-language abstracting journal in the mentioned branches. The abstrats are classified under more than a hundred subject categories, thus permitting a quick survey of the whole extended material. The AAA is a valuable and important publication for all students and scientists working in the fields of astronomy and related sciences. As such it represents a necessary ingredient of any astronomical library all over the world.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 804 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book Understanding the Structure of Molecular Clouds written by Jan Orkisz and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The new generation of wide-bandwidth high-resolution receivers turns almost any radio observation into a spectral survey. In the case of wide-field imaging of the interstellar medium, such a wealth of data provides new diagnostic tools, but also poses new challenges in terms of data processing and analysis. The ORION-B project aims at observing 5 square degrees of the OB molecular cloud, or about half of the cloud's surface, over the entire 3mm band. The emission of tens of molecular tracers has been mapped, including CO isotopologues, HCO, HCN, HNC, N2H+, methanol, SO, CN...Having access to spatially resolved maps from many molecular species enables us to identify the best tracers of the gas density and illumination. Machine learning techniques have also been applied to these maps, in order to segment the molecular cloud into typical regions based on their molecular emission, and to quantify the most meaningful correlations of different molecular tracers with each other and with physical quantities such as density or dust temperature.The wide-field coverage, together with the spatial and spectral resolution, also allows to characterize statistically the kinematics and dynamics of the gas. The amount of momentum in the compressive and solenoidal (rotational) modes of turbulence are retrieved, showing that the cloud is dominated by solenoidal motions, with the compressive modes being concentrated in two star-forming regions. This result is in line with the overall very low star formation efficiency of the cloud, and highlights the role of compressive forcing in the star formation process.The numerous filaments identified in the molecular cloud also prove to have rather low densities, and are very stable against gravitational collapse. Most filaments are starless, but they show signs of longitudinal and radial fragmentation, which indicates that star formation might occur later on.
Download or read book The Micro and Macro Physics of Giant Molecular Cloud Formation written by Kendall P. Hall and published by . This book was released on 2021 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: Giant molecular clouds are the birthplaces of stars, stars which gift back enriched gas, more endowed with metals than the gas they were formed from.Giant molecular clouds, as the formation sites of stars, are integral to the understanding of galaxy structure formation, star-formation, and ultimately the creation of life-bearing planets. They are complex structures, forming through difference mechanisms, all of which are important to study. For stars to be able to form, cool, molecular gas must exist. This work adds to the growing understanding of how molecules form on small scales,specifically how to trace molecular hydrogen gas that does not have corresponding CO emission: ``CO-dark" molecular hydrogen gas. Many tracers are suggested in the literature, but this thesis focuses on the use of the 158 micron line of C+, the 18 cm lines of OH, and the 9 cm lines of CH as diffuse gas tracers. They are studied in the context of two photodissociation regions/cloud boundaries in the Perseus giant molecular cloud. [CII] emission is found to better correlate with neutral atomic gas, whereas OH correlates well with visual extinction and molecular hydrogen depending on the gas density, and CH correlates best with molecular hydrogen. The conversion between CH integrated intensity and molecular hydrogen column density has less scatter than any other conversion factor, including those for 12CO, OH, and [CII]. This work also encompasses the formation of giant molecular clouds on larger scales. A currently ongoing project aims to study thermal pressure across an individual molecular cloud, for the first time showing observationally how the pressure changes within the different environments of a single cloud.
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 974 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Recent Advances in the Collapse and Fragmentation of Turbulent Molecular Cloud Cores written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation of Giant Molecular Clouds (GMCs) sets the stage for the formation of protostellar systems by the gravitational collapse of dense regions within the GMC that fragment into smaller core components that in turn condense into stars. Developing a comprehensive theory of star formation remains one of the most elusive, and most important, goals of theoretical astrophysics. Inherent in the difficulty in attaining this goal is that the gravitational collapse depends critically upon initial conditions within the cores which only recently have been known with sufficient accuracy to permit a realistic theoretical attack on the problem. Observations of stars in the vicinity of the Sun show that binary systems are prevalent and appear to be a general outcome of the collapse and fragmentation process. Despite years of progress, theoretical studies have still not determined why binary stars occur with such frequency, or indeed, even what processes determine the transition from single stars to binaries and thence to multiple stellar systems. One of the major goals of this research is to understand the nature of the formation of binary and multiple stellar systems with typical low mass stars 0.2 to 3 M{sub {circle_dot}} and the physical properties of these systems. Basic questions concerning this process remain unanswered. What determines the fraction of an unstable cloud that will fragment into protostellar objects? What determines the pattern of stellar clustering into binaries and multiple systems? Even after fragmentation occurs, we have little understanding of the subsequent collapse. Consequently, it is unclear how the mass distribution of fragments maps onto eventual stellar masses, something we must understand to explain the stellar initial mass function (IMF). We will first discuss the development of the numerical methodology that will contribute to answering these questions. This technology consists of a 3D parallel, adaptive mesh refinement (AMR) self-gravitational, radiation-hydrodynamics code that we have developed. We will present new results for the gravitational collapse and fragmentation of marginally stable turbulent molecular cloud cores and follow the collapse of high mass fragments as they interact with the radiation of the protostars forming at their centers. We will discuss the theoretical difficulties in forming binary stars and the role of turbulence in their formation.
Download or read book Dynamics of molecular clouds turbulent fragmentation and star formation written by P. Padoan and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 1248 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Fragmentation of molecular clouds written by Ralf S. Klessen and published by . This book was released on 1998 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Handbook of Star Forming Regions The northern sky written by Bo Reipurth and published by . This book was released on 2008 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Handbook describes the 6̃0 most important star forming regions within approximately 2 kpc, and has been written by a team of 105 authors with expertise in the individual regions. It consists of two full-color volumes, one for the northern and one for the southern hemisphere, with a total of over 1900 pages. The Handbook is full of stunning color images from some of the best astrophotographers, complementing the extensive research, figures, and tables presented by the authors. These volumes aim to be a source of comprehensive factual information about each region, with extensive references to the literature. A useful reference guide for both researchers and students, the Handbook provides a unique and detailed presentation of our current knowledge about the nearest and most important star forming regions.
Download or read book Fundamentals of Galaxy Dynamics Formation and Evolution written by Ignacio Ferreras and published by UCL Press. This book was released on 2019-04-02 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galaxies, along with their underlying dark matter halos, constitute the building blocks of structure in the Universe. Of all fundamental forces, gravity is the dominant one that drives the evolution of structures from small density seeds at early times to the galaxies we see today. The interactions among myriads of stars, or dark matter particles, in a gravitating structure produce a system with fascinating connotations to thermodynamics, with some analogies and some fundamental differences. Ignacio Ferreras presents a concise introduction to extragalactic astrophysics, with emphasis on stellar dynamics, and the growth of density fluctuations in an expanding Universe. Additional chapters are devoted to smaller systems (stellar clusters) and larger ones (galaxy clusters). Fundamentals of Galaxy Dynamics, Formation and Evolution is written for advanced undergraduates and beginning postgraduate students, providing a useful tool to get up to speed in a starting research career. Some of the derivations for the most important results are presented in detail to enable students appreciate the beauty of maths as a tool to understand the workings of galaxies. Each chapter includes a set of problems to help the student advance with the material.
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 The First Stars written by Volker Bromm and published by Springer. This book was released on 2016-09-07 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation of the first stars (Pop III stars) and galaxies is one of the great outstanding challenges in modern astrophysics and cosmology. The first stars are likely key drivers for early cosmic evolution and will be at the center of attention over the next decade. The best available space and ground-based telescopes like the Hubble Space Telescope probe the Universe to high redshifts and provide us with tantalizing hints; but they cannot yet directly detect the first generation of stars and the formation of the first galaxies. This is left as key science for future telecopes like the James Webb Space Telescope. This book is based in part on classroom tested lectures related to Pop III stars, but also draws from the author's review articles of the main physical principles involved. The book will thus combine pedagogical introductory chapters with more advanced ones to survey the cutting-edge advances from the frontier of research. It covers the theory of first star formation, the relation between first stars and dark matter, their impact on cosmology, their observational signatures, the transition to normal star formation as well as the assembly of the first galaxies. It will prepare students for interpreting observational findings and their cosmological implications.
Download or read book The Initial Mass Function 50 Years Later written by Edvige Corbelli and published by Springer Science & Business Media. This book was released on 2007-10-06 with total page 551 pages. Available in PDF, EPUB and Kindle. Book excerpt: Theideatocelebrate50yearsoftheSalpeterIMFoccurredduringtherecent IAU General Assembly in Sydney, Australia. Indeed, it was from Australia that in July 1954 Ed Salpeter submitted his famous paper "The Luminosity Function and Stellar Evolution" with the rst derivation of the empirical stellar IMF. This contribution was to become one of the most famous astrophysics papers of the last 50 years. Here, Ed Salpeter introduced the terms "original mass function" and "original luminosity function", and estimated the pro- bility for the creation of stars of given mass at a particular time, now known as the "Salpeter Initial Mass Function", or IMF. The paper was written at the Australian National University in Canberra on leave of absence from Cornell University (USA) and was published in 1955 as 7 page note in the Astroph- ical Journal Vol. 121, page 161. To celabrate the 50th anniversary of the IMF, along with Ed Salpeter’s 80th birthday, we have organized a special meeting that brought together scientists involved in the empirical determination of this fundamental quantity in a va- ety of astrophysical contexts and other scientists fascinated by the deep imp- cations of the IMF on star formation theories, on the physical conditions of the gas before and after star formation, and on galactic evolution and cosmology. The meeting took place in one of the most beautiful spots of the Tuscan countryside, far from the noise and haste of everyday life.
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.
