Quasars discovered
Quasars, or quasi-stellar objects, are extremely luminous astronomical entities that were first identified in the 1960s. Initially mistaken for stars due to their appearance in optical telescopes, their true nature was uncovered through the study of their light spectra, which revealed unusual emission lines. Notably, astronomer Maarten Schmidt discovered that these emission lines were redshifted, indicating that the quasars were moving away from Earth at incredible speeds—up to 45,000 kilometers per second. This redshift suggested that quasars are located at vast distances, often billions of light-years away, and they can emit light up to a hundred times brighter than the largest known galaxies.
The discovery of quasars posed significant challenges for astronomers, particularly regarding the apparent discrepancy between their small size and immense luminosity, leading to ongoing debates about their nature and the validity of redshift interpretations. This intrigue has continued for decades, with various theories proposed to explain quasars, though consensus remains elusive. The exploration of quasars highlights the complexities of our universe and the evolving understanding of cosmic phenomena.
Quasars discovered
Date: 1963
One of the most puzzling discoveries in the history of astronomy. The evidence that quasars were the strongest, though smallest, sources of energy yet detected in the universe implied that there might be great defects in the understanding of astronomy and physics.
Origins and History
In the 1940’s, astronomers found that radio telescopes could be constructed to detect distant sources of radio waves that were beyond the reach of visible light. During the 1950’s and 1960’s, astronomers used radio interferometers, which combined the resources of several radio telescopes, to determine the precise positions of the strongest radio sources.
The Discovery
When viewing the locations of radio sources with optical telescopes, astronomers occasionally saw what they thought to be a star within the same galaxy as Earth. Because the spectrum of a star’s light can reveal much about its composition, Allan Sandage, at the Hale Observatory in 1960, photographed the spectrum of one such “star.” He was surprised to discover that the spectrum contained emission lines that no one could identify.
In 1963, Maarten Schmidt at the California Institute of Technology discovered that the emission lines of one of these starlike objects were identical to hydrogen lines, except they were situated farther toward the red end of the spectrum. Schmidt used the same logic employed by Edwin Hubble, who in the 1920’s noted that because the emission lines of spectrum light from other galaxies were redshifted, the wavelengths of such light must be longer, meaning the galaxies were moving away from Earth. Schmidt decided that his “star” was rapidly moving away from Earth, at the enormous speed of about forty-five thousand kilometers per second, or about 15 percent of the speed of light. Using Hubble’s law for determining distance, Schmidt found that this “star” was far outside the galaxy, nearly three billion light years away.
Many more of these starlike objects were discovered during the 1960’s. They acquired the name “quasi-stellar object,” later shortened to “quasar,” because they resemble stars when viewed with an optical telescope. Astronomers decided that if the distance determined by redshift was accurate, quasars could typically emit light about a hundred times as bright as the largest galaxy then known. However, because the intensity of light from a quasar could fluctuate from one night to the next, the size of a quasar could be very small, comparable to that of the solar system containing Earth.
Impact
The discovery of quasars created a powerful dilemma among astronomers. They could not come to a consensus that reconciled the conflict between the apparent size of a quasar and its luminosity. Any denial of Hubble’s interpretation of redshift would compromise many widely accepted beliefs based on his conclusions, such as the expanding universe. Throughout the 1960’s, the nature of quasars remained unclear. To account for theoretical contradictions, astronomers in later years attempted both to analyze quasars without using redshift and to offer multiple interpretations of redshift, such as the presence of an intense gravitational field. Even decades after the discovery of quasars, however, none of the diverse solutions to the problem received universal acceptance.
Additional Information
A description of the quasars discovered in the 1960’s and a discussion of various theories about them can be found in William J. Kaufmann III’s Galaxies and Quasars (1979).