Quasars And Pulsars
Some of the most interesting objects in the sky have been discovered by using the techniques of radio astronomy. Included among these are the quasars and pulsars. When quasars were first discovered in 1960, they startled astronomers because they appeared to be stars that emitted both visible and radio radiation in very large amounts. Yet there was no way to explain how stars could produce radio waves in such significant amounts.
Eventually, astronomers came to the conclusion that these objects were actually star-like objects they named Quasi-Stellar Objects (QSOs), or quasars, rather than actual stars. An important breakthrough in the study of quasars occurred when astronomers measured the red-shift of the light they produced. That red-shift was very great indeed, placing some at distances of about 12 billion light-years from Earth. At that distance, quasars may well be among the oldest objects in the sky. It is possible, therefore, that they may be able to provide information about the earliest stages of the universe's history. It is now thought that quasars are the very bright centers of some distant galaxies, and so energetic probably because there is a supermassive black hole at the galaxy's center.
Another valuable discovery made with radio telescopes was that of pulsars. In 1967, British astronomer Jocelyn Bell noticed a twinkling-like set of radio signals that reappeared every evening in exactly the same location of the sky. Bell finally concluded that the twinkling effect was actually caused by an object in the sky that was giving off pulses of energy in the radio portion of the electromagnetic spectrum at very precise intervals, with a period of 1.3373011 seconds. She later found three more such objects with periods of 0.253065, 1.187911, and 1.2737635 seconds. Those objects were soon given the name of pulsars (for pulsating stars). Evidence appears to suggest that pulsars are rotating with very precise periods, and they are now believed to be rotating neutron stars that emit a narrow beam of radio waves. Because the star is rotating, the beam sweeps across our sky with a precise period.
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David E. Newton
Science EncyclopediaScience & Philosophy: Quantum electronics to ReasoningRadio Astronomy - Origins Of Radio Astronomy, Radio Vs. Optical Astronomy, Radio Telescopes, Increasing Resolution In A Radio Telescope