Starbursts

This book reviews the importance of massive stars in several areas of astrophysics. Massive stars are objects that are 10-100 times the mass of our Sun. Above ten solar masses, loss through stellar winds begins to have a major impact on the evolution of a star. The upper limit of 100 solar masses is derived from observations. Significant progress has now been achieved in massive star research. New models, along with high quality observations, have improved our understanding of the formation, structure, atmosphere, and evolution of these massive objects. They are formed in violent bursts of star formation and are probably related to the phenomena observed in active galactic nuclei. The workshop at the Space Telescope Science Institute examined the interplay between the astrophysics of massive stars and their location in extragalactic starburst regions. There are eighteen chapters by leading researchers. Each has been carefully edited to ensure that the book is a comprehensive introduction to the theory and observation of massive stars in starburst regions.

Starbursts are important features of early galaxy evolution. Many of the distant, high-redshift galaxies we are able to detect are in a starbursting phase, often apparently provoked by a violent gravitational interaction with another galaxy. In fact, if we did not know that major starbursts existed, these conference proceedings testify that we would indeed have difficulties explaining the key properties of the Universe! These conference proceedings cover starbursts from the small-scale star-forming regions in nearby galaxies to galaxy-wide events at high redshifts; one of the major themes of the conference proved to be "scalability", i.e., can we scale up the small-scale events to describe the physics on larger scales. The key outcome of this meeting – and these proceedings – is a resounding "yes" to this fundamental, yet profound question. The enhanced synergy facilitated by the collaboration among observers using cutting-edge ground and space-based facilities, theorists and modellers has made these proceedings a true reflection of the state of the art in this very rapidly evolving field.

Starbursts are regions of unusually rapid star formation, often located in the central parts of galaxies. They differ from more normal regions of star formation in terms of the throughput of mass and the rapidity with which the gas is consumed. In the last twenty years, extensive observational data at most wavelengths have become available on starbursts, but many important issues remain to be addressed, observationally as well as theoretically. How are strong episodes of star formation triggered? What is the quantity of gas converted into stars during bursts? What is the initial mass function of stars in these events? How does the feedback from stars influence the interstellar medium and self-regulate star formation? What is the subsequent chemical and photometric evolution? How do starbursts rule the formation and evolution of galaxies? In recent years, many observational data at different wavelengths (optical, radio, infrared, X-ray) have become available. However, these observations are still fragmentary in the sense that different classes of objects have been observed in different ways, and the coverage is not consistently deep or complete. As a consequence, an overall observational picture of starburst galaxies is missing, and theoretical understanding and modelling have remained highly tentative. The purpose of the school Starbursts: Triggers, Nature, and Evolution was to gather theorists and observers with complementary approaches to the starburst phenomenon, in order to summarize the state-of-the-art of the observations and models, emphasizing the consistency of the various viewpoints.

A major fraction of star formation in the universe occurs in starbursts. These regions of particularly rapid star formation are often located towards the centers of host galaxies. Studies of this kind of star formation at high redshift have produced astonishing results over recent years that were only possible with the latest generation of large ground-based and space telescopes. The papers collected in this volume present these results in the context of the much firmer foundation of star formation in the local universe, and they emphasize all the important topics, from star formation in different environments to the cosmic star formation history.