The Black Hole may have captured the imagination of the general public as the most intriguing of the many new astrophysical concepts, but it is the Quasar (Quasi-stellar Object) that has most puzzled astronomers.
In 1960, optical astronomers found a star-like object at the position given for the radio source 3C 48 (Third Cambridge Catalog). The star-like object appeared as a 16th magnitude star whose spectrum exhibited broad emission lines that could not be identified. In addition, the object emitted far more radiation in the ultra-violet than an ordinary star and its brightness varied by more than 40% in a year. 3C 48 was thought to be some kind of radio-emitting star located in our galaxy.
In early 1963 another radio source, 3C 273, was identified with a star-like object even brighter than 3C 48, only this time it was recognized that most of the puzzling lines in its spectrum could be explained as the Balmer series of Hydrogen lines shifted in wavelength toward the red -- a red shift. In other words, this suggested that this new class of objects were cosmological (very distant) in origin, rather than members of our galaxy.
What puzzled astronomers was that optical photographs of these objects showed them to be pinpoints of light (with no extended envelopes of emission), which might suggest spiral-arms, and thus galaxies. The redshift (distance indicator) associated with normal external galAxi6s was in the case of these new objects very much larger. Here were what appeared to be stars that apparently were objects at more extreme distances than any external galaxy ever discovered. And that was only the beginning!
The term "Quasi-stellar Objects" was coined and thus the nick-name Quasars, The mystery of these objects deepened. The problem was that if the distance of these objects corresponded to their redshift, then they were thousands of millions of light years away. The fact that we could pick up any kind of radio signal from such distant objects suggested that they were enormously powerful radiators of energy, beyond anything we had known. As a final straw, astronomers had to consider that these remote objects possessed variability! Lets explain why this was so very hard for astronomers to digest:
It is a fundamental astronomical concept that very distant objects are so enormous (large diameters) that they could not possibly show any variations over time scales that human beings might ever measure. For instance, a distant galaxy might be some 50,000 light years in diameter. If it suffered a profound explosion within itself, this information (travelling at the speed of light) would take several tens of thousands of years to illuminate the entire galaxy in question, too long to catch our notice. Yet the first quasar whose redshift was measured (3C 273) showed variability from year to year for over eighty years. Astounding! Any object that varies on a time scale of a single year cannot be much larger than a light year in size. At the proposed distance for quasars, this would indicate that a tiny source was emitting more light and energy than an entire galaxy of stars! Subsequently quasars have been discovered that vary over a period of months and even days.
Whatever is responsible for the enormous energy output ii quasars must be small and massive -- perhaps with a mass as large as 10 million Suns. One of the side effects of these discoveries was that optical and radio astronomers could come together in mutual awe and wonder for the first time. Previous to quasars, there had been no joint project between these two very different kinds of astronomers.
The radio astronomers had not sprung from the midst of established optical astronomy, but had gathered together from several other disciplines, not previously associated with the "educated" circle of astronomers, such as radio hardware personnel. In fact many of the early papers on radio astronomy exist only in the purple ink of the "spirit" duplicator process, rather than offset printing, much less sewn signatures. Astrologers today find themselves in much the same positions that radio astronomers were in several decades ago: entering the established order from the fringe, rather than from the center.
A long and interesting controversy arose among astronomers as to the nature of quasars. Many felt that quasars might be more near and smaller objects engaged in an intense gravitational struggle, causing the shift in spectra toward the red, and so on. Today it is (more or less) generally accepted that quasars are objects located at cosmological distances, rather than near distances. Many astronomers feel that quasars are members of a group that includes the Seyfert galaxies, N galaxies, and BL Lacertae objects. Quasars have been found to emit radiation at almost all frequencies, including the x-ray. Quasars are brighter at increasing wavelengths and their radiation is partially plane polarized. This suggests that the source of energy is synchroton radiation, which is emitted by high-energy electrons spiraling around the lines of force in a magnetic field. It is currently being suggested that the ultimate source of such great energy as we find in quasars must be the black hole and that these objects must either already be black holes or will become such in a very short time.
It is also interesting to note that if quasars are indeed very remote objects, we see in them the universe, as it was a very long, long time ago, not long after the so-called beginning.
Copyright (c) 1997-99 Michael Erlewine