Chapter summary

In this chapter we looked at the properties of various types of galaxies.

Elliptical galaxies have no evidence for recent star formation. However, the metal abundances are high. Ellipticals are classified according to the eccentricity of their appearance. Spirals have an evident interstellar medium, as well as O and B stars, meaning that star formation is still taking place. Spirals are classified according to the tightness of the spiral arms and the relative sizes of the nucleus and disk.

We applied some of the ideas of star formation, discussed in previous chapters, to look at star formation in the LMC and in spirals. We also looked at how the density wave theory might explain spiral structure.

In studying rotation curves of galaxies we found that the masses of galaxies are greater than would be determined from luminous material. It has been suggested that most of the matter is distributed in a spherically symmetric halo.

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