Fragmentation of Molecular Clouds and Star Formation


Book Description

A few years ago, a motivation for organizing one more IAU Symposium on star for mation in Grenoble, was the anticipated completion of the IRAM interferometer on the Plateau de Bures, close to Grenoble. This choice was also a sort of late celebration of the genius of Joseph Fourier, born in Grenoble, whose work is the very fondation of in terferometry. At the time when we finally announced the advent of this conference, the first reactions we got from the community were expressions of saturation and even reject, the Symposium being unfortunately scheduled almost simultaneously as two other major meetings on closely related topics, and sponsored by different organizations. A wave of disappointment then reached the organizers. Some of us were enthusiastic enough to help the others overcome their discouragement. Let them be thanked here. There was, indeed, a deeper motivation for organizing this conference. It was to trigger the meeting and communication of physicists and astrophysicists since many of the difficulties met now in understanding the physics of the interstellar medium and its evolution toward star formation are common to several, if not most, other fields of physics. They are assigned to one origin: complexity.




The Earliest Stages of Massive Clustered Star Formation: Fragmentation of Infrared Dark Clouds


Book Description

This thesis presents an in-depth, high-resolution observational study on the very beginning of the formation process: the fragmentation of dense molecular clouds known as infrared dark clouds (IRDCs). Using the Submillimeter Array (SMA) and Very Large Array (VLA) radio interferometers, the author has discovered a common picture of hierarchical fragmentation that challenges some of the leading theoretical models and suggests a new, observation-driven understanding of how massive star formation in clustered environments may begin: it is initiated by the hierarchical fragmentation of a dense filament from 10 pc down to 0.01 pc, and the stellar mass buildup is simultaneously fed by hierarchical accretion at similar scales. The new scenario points out the importance of turbulence and filamentary structure, which are now receiving increasing attention and further tests from both observers and theorists.




The Initial Mass Function 50 Years Later


Book Description

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.




Principles of Star Formation


Book Description

Understanding star formation is one of the key fields in present-day astrophysics. This book treats a wide variety of the physical processes involved, as well as the main observational discoveries, with key points being discussed in detail. The current star formation in our galaxy is emphasized, because the most detailed observations are available for this case. The book presents a comparison of the various scenarios for star formation, discusses the basic physics underlying each one, and follows in detail the history of a star from its initial state in the interstellar gas to its becoming a condensed object in equilibrium. Both theoretical and observational evidence to support the validity of the general evolutionary path are presented, and methods for comparing the two are emphasized. The author is a recognized expert in calculations of the evolution of protostars, the structure and evolution of disks, and stellar evolution in general. This book will be of value to graduate students in astronomy and astrophysics as well as to active researchers in the field.




Molecular Clouds


Book Description

The study of molecular clouds has received increasing interest over recent years, particularly in the UK with the advent of powerful new instruments such as MERLIN and the Maxwell millimetre wave telescope. This book is based on the proceedings of the Seventh Manchester International Astronomy Conference which brought together an international list of speakers to discuss important new developments in this field. The book covers a wide range of topics relevant to the general subject of molecular clouds, with review articles and papers from an impressive list of contributors. Much new work in this area is covered, and consequently this book should become an important reference source for workers in this and related fields.







Present-day and Early Star Formation


Book Description

Stars form from molecular cloud cores by gravoturbulent fragmentation. Understanding the angular momentum and the thermal evolution of cloud cores thus plays a fundamental role in completing the theoretical picture of star formation. This is true not only for current star formation as observed in regions like the Orion nebula or the -Ophiuchi molecular cloud but also for the formation of stars of the first or second generation in the universe. In this thesis we show how the angular momentum of prestellar and protostellar cores evolves and compare our results from hydrodynamical simulations with observed quantities. We find that collapse induced by gravoturbulent fragmentation is accompanied by a substantial loss of specific angular momentum. This eases the "angular momentum problem" in star formation. The distribution of stellar masses at birth (the initial mass function, IMF) is another aspect that any theory of star formation must explain. Our investigation generally supports the idea that the distribution of stellar masses depends mainly on the thermodynamic state of the gas.




Star Formation in Galaxy Evolution: Connecting Numerical Models to Reality


Book Description

This book contains the elaborated and updated versions of the 24 lectures given at the 43rd Saas-Fee Advanced Course. Written by four eminent scientists in the field, the book reviews the physical processes related to star formation, starting from cosmological down to galactic scales. It presents a detailed description of the interstellar medium and its link with the star formation. And it describes the main numerical computational techniques designed to solve the equations governing self-gravitating fluids used for modelling of galactic and extra-galactic systems. This book provides a unique framework which is needed to develop and improve the simulation techniques designed for understanding the formation and evolution of galaxies. Presented in an accessible manner it contains the present day state of knowledge of the field. It serves as an entry point and key reference to students and researchers in astronomy, cosmology, and physics.




The Formation of Stars


Book Description

This book is a comprehensive treatment of star formation, one of the most active fields of modern astronomy. The reader is guided through the subject in a logically compelling manner. Starting from a general description of stars and interstellar clouds, the authors delineate the earliest phases of stellar evolution. They discuss formation activity not only in the Milky Way, but also in other galaxies, both now and in the remote past. Theory and observation are thoroughly integrated, with the aid of numerous figures and images. In summary, this volume is an invaluable resource, both as a text for physics and astronomy graduate students, and as a reference for professional scientists.