Quasar light to trace the expansion of the universe

Quasar light to trace the expansion of the universe

a series of circles expanding from left to right

This drawing illustrates how astronomers of the third Sloan Digital Sky Survey (SDSS-III) used quasar light to trace the expansion of the universe. The expansion is shown by the circular disks of increasing area from left to right. From the Big Bang, the expansion occurs rapidly, then slows down, then speeds up again as dark energy pushes apart walls and filaments of galaxies at different distances (purple). As light travels to us from very distant quasars (white dots on the left), it passes through the expanding universe, carrying with it the story of its journey through this expanding cosmic web. Astronomers have measured the expansion of the universe by tracing how quasar light has passed through these structures.  

Image: Paul Hooper at Spirit Design, with Mat Pieri and Gongbo Zhao, ICG
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