Our knowledge of the galaxies, especially their origin and evolution, is inadequate. How each of them materialized, endowed with peculiar shapes and prodigious energies, remains largely unsolved. Their enigma is deepened by the fact that astronomers cannot find any galaxy unambiguously in the act of formation. Parts of all of them seem almost as old as the Universe itself, their youthful exuberance still beyond the clear reach of our best telescopes. Furthermore, even when galaxies do evolve, their changes are so agonizingly slow, compared to the duration of our technological civilization, as to make them appear immutable. If our understanding of galaxies seems sketchy, that’s because it is; in some ways, galaxy research is only now coming into its own.
Currently, the origin and evolution of galaxies tender more problems than the formation of stars, which we can observe directly; than the evolution of stars, which we understand rather well; than the origin of life, which we can assess in our laboratories; than the evolution of life, which we can study in action; even than the origins of intelligence, culture, and technology, all of which we can probe tangibly with fossils and artifacts unearthed from layers of historical rubble. Practically everything else discussed in this Web site is on firmer ground than the origin and evolution of galaxies. Exempt those eternal perplexities about the origin of the Universe itself, the subject of galaxy formation is the foremost missing link in the scenario of cosmic evolution.
Galaxies, though, are so very important. Apart from the creation of simple atoms, the formation of galaxies (perhaps along with some massive, extinct stars) was the first great accomplishment of the Matter Era. Until we learn a great deal more about how gravity leverages even slight initial gas irregularities into conspicuous density contrasts, our understanding of galaxy origins, and hence of cosmic evolution, will remain incomplete and unsatisfactory. Yet the promise is great, the potential payoff even greater. With the physicists unable to build accelerators on Earth sufficiently energetic to reproduce the earliest instants of time, it is the astronomers who, by studying the macrorealm of galaxies and their large-scale structure, are beginning to provide tests, albeit indirect ones, of the grand unification of particles and forces in the microrealm.
Astronomers now stand on the threshold of a golden age of galaxy research, much of which is a century or so behind stellar research if only because the galaxies are so dim and distant and therefore tricky to study. The equipment scheduled to debut during the early decades of the new millennium will have greater sensitivity to collect more radiation as well as higher resolution to clarify the spread of that radiation, thereby almost surely advancing our knowledge of the origin and evolution of galaxies. Over the entire range of phenomena—from the earliest onset of density fluctuations in the primordial Universe, through the emergence of activity in the centers of galaxies, and on to the slow conversion of galactic gas into stars and planets—observations with novel instruments on the ground and robot telescopes in orbit are poised to provide a wealth of new and exciting data that hold clues to nothing less than some of the most profound and ancient cosmic secrets.
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Ferris, T., The Whole Shebang, 1997, Simon & Schuster, New York.
Hodge, P. and Waller, W., Galaxies, 2003, Harvard University Press, Cambridge.
Kirshner, R., Extravagant Universe, 2002, Princeton Univ. Press, Princeton.
Silk, J., The Big Bang, 2001, W.H.Freeman, San Francisco.
NASA Science on the Internet :
http://www.science.nasa.govHarvard-Smithsonian Center for Astrophysics:
http://www.cfa.harvard.eduExtragalactic Database:
http://nedwww.ipac.caltech.edu