While radio galaxies were often visible on optical photographs, back in the 1960s another type of radio source was found that appeared to have no optical counterpart. At the very best, astronomers might have noticed what appeared to be a star at the location of the radio source, but normal stars do not produce strong radio emissions. If those were stars they had to be a special class of objects and the name radio “star” was adopted, at least for a while, until one of the most amazing breakthroughs in the history of astronomy.
KeywordsRadio Emission Radio Source Radio Galaxy Brightness Variation Radio Brightness
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