MAGNETIC-FIELDS IN GALAXIES

Recent years have seen an amazing development in our knowledge of the magnetic fields in the universe. The last ten years were crucial in ou r realization Of the importance of the magnetic fields in galaxies. Wh ile a lot of the earlier data on our Galaxy depended on optical observ ations, the bulk of the recent results depend on radio measurements. T he radio Zeeman effect gave us new information on magnetic fields in m olecular clouds. The mapping of galaxies at several radio frequencies resulted in new knowledge about the large-scale magnetic fields in the se basic building blocks of the universe. These exciting observations have led to new theoretical developments. In particular, the dynamo th eory of flat objects received much attention since the observed large- scale structures can best be explained through the action of the dynam o effect. This review will attempt to summarise the observational evid ence and to give viable explanations for the magnetic fields in galaxi es.