Galaxy evolution in the early universe
Shapiro, Kristen L. Department of Astronomy, University of California, Berkeley, California.
- Looking backward through the universe
- The nature of galaxies in the early universe
- Drivers of galaxy evolution
- Linking galaxies across cosmic time
- Links to Primary Literature
- Additional Readings
Galaxies are the fundamental building blocks of the universe. There are several hundred billion galaxies in the universe, each containing tens to hundreds of billions of stars. In the local universe, three general classes of galaxies are observed: spiral, irregular, and elliptical. Spiral galaxies, such as the Milky Way, are stellar systems characterized by a thin, rotating disk surrounding a central spherical bulge (Fig. 1). A small fraction of the matter in these galaxies (roughly 5%) is gas, located primarily in the thin disk and continuously forming new stars. Irregular galaxies are the less massive cousins of spiral galaxies; these systems have slightly larger gas fractions, little or no coherent spiral structure in their disks, and no central bulge. At the other extreme, elliptical galaxies are gas-poor, roughly spherical systems that resemble scaled-up bulges.
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