Most of the visible matter in the universe is contained in galaxies, which are agglomerations of several billions of stars held together by their mutual gravity.
Galaxies come in a great range of shapes and sizes.
The most common types are gas-rich spirals, such as our own Milky Way, or elliptical galaxies that exhibit much less rotation and contain much less interstellar material. Under normal conditions stars die and are reborn at a slow, steady rate while they move in stable orbits around the galaxy s center. In an important minority of galaxies, however, a collision or some other factor causes the galaxy to become anomalously bright for a limited period. At the IfA we study both normal and pathological galaxies in an effort to understand their origins and evolution. Normal Galaxies Robert Joseph studies the infrared emission from normal spiral galaxies.