Transformation of Galaxies within the Hubble Sequence
Abstract
It becomes increasingly clear that galaxies must no longer be seen as dynamically quiet systems. On the contrary for many different reasons the life of almost all galaxies is marked by "events" involving global dynamics which transform significantly their shapes. These global transformations are not arbitrary, but follow the observed characteristics that galaxies are known to possess: de Vaucouleurs or exponential profiles, correlations across the Hubble sequence, etc. In addition, the sense of evolution is not arbitrary but must in most situations follow the sense of the irreversible processes taking place in galaxies, such as the transformation of gas into stars. Thus galaxies evolve from the dark matter dominated late type galaxies to the star dominated early type galaxies. The properties of the Hubble sequence are such that over Gyrs dark matter appears to transform into stars, which is plausible only if a substantial part of dark matter is in the form of undetected gas. The most promising forms are cold gaseous or solid molecular hydrogen and gaseous He.
- Publication:
-
H2 in Space
- Pub Date:
- 1999
- Bibcode:
- 1999h2sp.confE..47P