The Discovery of Radio Sources

Abstract

In the last chapter we saw that the white fuzzy objects in the sky were eventually shown to be island universes of stars—galaxies. Some of these galaxies are spirals, others ellipticals, and a few have little or no form. But galaxies differ in more than just form. Some are much more active than others, with cores that eject energetic radiation and particles. To us they appear as if they are exploding, for we frequently see long plumes of gas and stars, and in a few cases we even see jets emanating from them. Most galaxies, however, show little evidence of activity. Our Milky Way galaxy, for example, would show none if viewed from a distance. A close look at its core, however, reveals that it too is energetic. How do we know? Although optical telescopes don’t show it, other types of telescopes do.