4 - Quasars as cosmological probes

Summary

Galactic envelopes of quasars

The discovery of quasars heralded the present era of astrophysics, characterized by wide ranging investigations of every part of the spectrum, whether easily accessible or not. Observers were stimulated to open new spectral windows, primarily in the hope of finding something as extraordinary and unexpected as the quasars. None succeeded. Even when observations were pushed to X-ray wavelengths, quasars stood out. When discovered, quasars came as a stunning surprise to the small community of theoreticians who dabbled in extragalactic astrophysics. The quasars seemed so unlike galaxies that it was not clear whether their redshifts should be interpreted with the same cosmological relations that applied to galaxies. Doing so gave unbelievable answers; the quasars were just too luminous to explain. Furthermore, surprise piled upon surprise, these luminosities arose in volumes so small that luminosity variations could be seen in times of less than a year. It was fair, even necessary, to question any assumptions made for quasars, including assumptions about cosmological redshifts. I have argued at some length (Weedman 1976), so will not repeat much of it here, that this bewilderment arose as a consequence of the sequence of discovery for quasars. Had quasars been discovered initially as events in the nuclei of galaxies, the nature of their redshifts would have never been questioned. As it happened, it was only realized after the fact that identical phenomena can be observed in galactic nuclei.