![]() Elaborate tables had been published showing the lines that each element would produce under a wide range of conditions. By the 1960s, astronomers had a century of experience in identifying elements and compounds in the spectra of stars. Spectra of these radio “stars” only deepened the mystery: they had emission lines, but astronomers at first could not identify them with any known substance. The answer came when astronomers obtained visible-light spectra of two of those faint “blue stars” that were strong sources of radio waves ( Figure 27.2). What then were these “quasi-stellar radio sources”? Redshifts: The Key to Quasars As they improved the images that their new radio telescopes could make, scientists discovered that some radio sources were in the same location as faint blue “stars.” No known type of star in our Galaxy emits such powerful radio radiation. Although few astronomers would have predicted it, the sky turned out to be full of strong sources of radio waves. The discovery of radio sources that appeared point-like, just like stars, came with the use of surplus World War II radar equipment in the 1950s. The name “ quasars” started out as short for “quasi-stellar radio sources” (here “quasi-stellar” means “sort of like stars”). Justify the statement that the enormous amount of energy produced by quasars is generated in a very small volume of space.Explain how astronomers determined that quasars are at the distances implied by their redshifts.By the end of this section, you will be able to:
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