Gerry Gilmore - Böcker

The subject of stellar populations touches on almost every field of astronomy and astrophysics. As well as commemorating the 50th anniversary of the beginnings of the subject, this book brings together experts on all relevant parts of astrophysics to discuss the outstanding questions relating to the stellar population concept as an observational tool that provides a physical understanding of the galaxies.

The subject of stellar populations touches on almost every field of astronomy and astrophysics. As well as commemorating the 50th anniversary of the beginnings of the subject, this book brings together experts on all relevant parts of astrophysics to discuss the outstanding questions relating to the stellar population concept as an observational tool that provides a physical understanding of the galaxies.

The Milky Way Galaxy offers a unique opportunity to study the structure and contents of a major stellar system in three dimensions, at high spatial and spectral resolution, and to very large galactocentric distances. This potential can be realised only by statistical surveys of large areas of the sky, and by detailed study of specific regions with exceptional properties, such as the Galactic centre, and of specific classes of object, such as the globular clusters. The acquisition of such data from a variety of ground-based and satellite surveys has been a primary topic of Galactic research for some years. Several such surveys have been completed recently, and have led to a substantial modification of our understanding of Galactic structure and evolution. The importance of the ability of satellite observatories to survey and to study wavelengths which are inaccessible from the ground is evident in the wealth of data discussed and analysed in this volume which is derived from satellites, specifically COS-B, HEAD-I, HEAO-3, IRAS, PIONEER-lO, SAS-2, and TENMA. The cru­ cial role of ground-based observations to complement and comprehend the satellite data is also well evident. Similarly, the major ground-based studies whose results are reported here illustrate the necessity for carefully conceived and executed very large scale surveys of many types of object and many parts of parameter space before a coherent picture of the Galaxy will be available.

The visible universe is a small perturbation on the material universe. Zwicky and Sinclair Smith in the 1930s gave evidence of invisible mass in the Coma and Virgo Clusters of Galaxies. Better optical data has only served to confound their critics and the X-ray data confirms that the gravitational potentials are many times larger than those predicted on the basis of the observed stars. Dynamical analyses of individual galaxies have found that significant extra mass is needed to explain their rotational velocities. On much larger scales, tens of megaparsecs, there is suggestive evidence that there is even more mass per unit luminosity. What is this non-luminous stuff of which the universe is made'? How much of it is there? Need there be only one kind of stuff? There are three basic possi bili ties:- all of it is ordinary (baryonic) matter, all of it is some other kind of (non-baryonic) matter, or some of it is baryonic and some is non-baryonic.