TALK ABSTRACT:
As early as 1784, discussions of dark stars were in the literature, although attempts to evaluate the density of these non-luminous objects were rare before the early part of 20th Century. In the second half of the 20th Century, observations with large optical and radio telescopes and spectrographs led to the surprising conclusion that most of the matter in the universe is dark. I will discuss the early history and the observations that led to this conclusion. I will also briefly examine alternatives to a universe in which most of the matter is not radiating.