The discovery of quasars in the early 1960s marked a turning point in astronomy and opened for us a vastly more immense vista on the universe. The tale of that discovery is completely fascinating, being best told by those closely involved. The main detail necessary here is that quasars appear as point-like optical sources, usually identified with radio sources, and having optical emission lines at large redshifts. The redshifts turned out to be much larger than anything seen previously, and if attributed to the Hubble expansion of the universe implied enormous distances and enormous energetics. Furthermore, it soon was discovered that many of them displayed variable brightness on time scales of weeks or less. That has been especially awkward for astronomers to understand since a source is not supposed to be able to turn on or off in a shorter time scale than the light travel time across the source. That should mean that sources are very small for their power, and yet there appear some forbidden emission lines only to be expected from low-density material.
KeywordsRadio Source Gravitational Lens Hubble Expansion Distant Quasar Light Travel Time
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