Over the last few years, our picture of the chemical evolution of the Galaxy has changed substantially. These changes are of interest because chemical evolution provides a common point of contact for most astrophysical processes of importance to galaxy evolution. By astrophysical processes we mean star formation, stellar nucleosynthesis, gas dynamics, etc. An understanding of galactic chemical evolution would allow us to place constraints on all of these topics simultaneously. This property, however, is a double-edge sword because, with so many variables involved, unique solutions to problems in chemical evolution are almost impossible.

We have calculated models for the kinematical and chemical evolution of the Galactic disk that include the infall of metal-free gas and the stochastic acceleration of disk stars. Our models are similar in some respects to those of Chiosi (1980) and Vader & de Jong (1981), but the results are compared with a greater variety of observational data. A complete description of this work will appear shortly in Monthly Notices of the Royal Astronomical Society.

In broad outline, the traditional picture for the formation of the Milky Way can be summarized as follows. The proto-galaxy consisted of a slowly rotating cloud of metal-free gas that cooled by bremsstrahlung and recombination radiation. As the internal pressure of the gas decreased, it collapsed in stages with smaller dimensions, faster rotation velocities and flatter shapes until it reached centrifugal support in a fundamental plane. At the same time, the gas was progressively depleted by the formation of stars and enriched with heavy elements by the ejecta from previous generations. The result is a general correlation between the kinematic properties, chemical compositions and relative ages of the stellar populations within the Galaxy. This picture was formulated at the Vatican symposium by Oort (1958) and others and was elaborated by Eggen, Lynden-Bell & Sandage (1962), Sandage, Freeman & Stokes (1970), Gott & Thuan (1976), Larson (1976) and others. Much of the recent work on galaxy formation has been an attempt to extend these ideas to a more comprehensive picture that includes large quantities of dark matter. The purpose of this article is to review several topics concerning the collapse phase in the evolution of the Milky Way.

Looking back with modern instrumentation like that at Westerbork to possible progenitors of galaxies, we find at increasing redshifts active galaxies, radio galaxies, BL Lac objects and quasars. With improving instrumental sensitivity and resolving power, energetic activity is discovered in these objects: ejecta of millions of solar masses, mostly bipolar, were thrown out from the central bodies to hundreds of kiloparsecs at nearly luminal speeds. The rich variety of their structures and energetics is illustrated in a review paper by Miley (1980). Like miniatures of these phenomena, ejections of 10–100 M⊙ with speeds of 10–100 km s-1 appear in star-forming regions of our Galaxy.

We have adapted the N-body code of Van Albada (1982) to study the secular evolution of a hot collisionless stellar component (E galaxy or galactic bulge) due to slow changes in another component of the same galaxy. Our equilibrium starting model is a non-rotating triaxial ellipsoid with axial ratios 1.3:1.4:2.0; the effects of the “other component” are then simulated by various simple means.

Gas dynamics plays a vital role in the formation and ongoing evolution of a disk galaxy through its ability to have dissipative collisions. In this paper the simplest possible gas physics which provides a description of a gaseous component is incorporated into N-body experiments to investigate the formation of a disk galaxy.

It is a decided honor to have the opportunity to address as distinguished a group as is present this evening, and I am particularly grateful for the very complimentary introductory remarks of Harry van der Laan. To paraphrase Einstein's comment on a dissimilar occasion, such a lovely preamble entails a risk that the packaging may prove better than the meat.

First let me review the historical discussions presented during our symposium: the papers by Paul, Gingerich, Hoskin and Smith. I was greatly impressed by the power of abstract human thought in its confrontation with resistant reality. On the one hand we see again and again extraordinary prescience, where abstract beliefs based on little or no empirical evidence–like the island-universe hypothesis–turn out to be, in their essentials, true. Clearly, we often know more than we know that we know. On the other hand, there are repeated instances of resistance to the most obvious truth due to ingrained beliefs. These may be termed conspiracies of silence. Van Rhijn and Shapley agreed about few things. But one of them was that there was no significant absorption of light in the Galaxy. Yet the most conspicuous feature of the night sky is the Milky Way, and the second most conspicuous feature is the dark rift through its middle. What looks to the most untutored eye like a “sandwich” was modeled as an oblate spheroid. These eminent scientists must have known about the rift, but somehow wished it away in their analyses. I find that very curious. Other examples from earlier times abound. We all know that the Crab supernova was seen from many parts of the globe but, though it was bright enough to be detected by the unaided eye in daylight, its existence was never–so far as we know–recorded in Europe. It did not fit in with the scheme of things, so it was not seen.