Black Holes: from Speculations to Observations

This paper provides a brief review of the history of our understanding and knowledge of black holes. Starting with early speculations on “dark stars” I discuss the Schwarzschild "black hole" solution to Einstein’s field equations and the development of its interpretation from "physically meaningless" to describing the perhaps most exotic and yet "most perfect" macroscopic object in the universe. I describe different astrophysical black hole populations and discuss some of their observational evidence. Finally I close by speculating about future observations of black holes with the new generation of gravitational wave detectors. THEORETICAL CONSIDERATIONS This paper summarizes a talk presented at the Albert Einstein Century International Conference, held in Paris, France, in July 2005 to mark the centennial of Einstein’s "miracle" year 1905. Strictly speaking, black holes are a consequence of another Einstein miracle that did not occur in 1905 and still had to wait ten years, namely general relativity. With his theory of special relativity, however, Einstein had laid the ground work already in 1905 for his theory of general relativity. And even more strictly speaking, speculations on black holes predate even the special theory of relativity by over a century.