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The eBOSS 3D map of the Universe (360)

“We know both the ancient history of the universe and its recent expansion history fairly well, but there’s a troublesome gap in the middle 11 billion years,” Kyle Dawson, a cosmologist at the University of Utah and lead researcher of the project,  said in a statement. “For five years, we have worked to fill in that gap.”

The gap begins a few billion years after the Big Bang. Scientists are able to measure the rate of the universe’s expansion before this thanks to the cosmic microwave background — ancient radiation left over from the infancy of the universe that researchers can still detect; and they can calculate recent expansion by measuring how the distance between Earth and nearby galaxies increases over time. But expansion in the middle period has been little studied because the light of galaxies more than a few hundred million light-years away can be incredibly faint. To fill in the gap, a team of more than 100 scientists from around the world looked at not just distant galaxies, but also bright-burning quasars (extremely luminous objects powered by the hungriest black holes in the cosmos).

Key to this survey is a phenomenon called redshift — a process by which light from the most ancient, distant galaxies is literally stretched by the expansion of the universe, increasing its wavelength and shifting it toward the redder end of the spectrum. As a result of this cosmic color-change, distant light sources appear redder, while those nearer to Earth look bluer…

 

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