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Spectra for Quasars Pinpoint the Birth of Light

Photonics Spectra
Nov 2001
Using the spectra from distant quasars taken by a 10-m telescope at W.M. Keck Observatory atop Mauna Kea, Hawaii, two teams of astronomers have suggested that the so-called cosmic Dark Ages came to an end approximately 900 million years after the big bang. The Dark Ages refer to a time in the history of the universe in which atomic hydrogen, formed from free electrons and protons approximately 300,000 years after the big bang, absorbed all light from the newly forming protogalaxies. Over time, ultraviolet light reionized the atomic hydrogen and allowed light to travel freely.

One team, representing 18 institutions from the US, Hungary and Japan, looked at changes in absorption in the spectra from four quasars at redshifts of up to 6.28. The other, which included researchers from California Institute of Technology and the Jet Propulsion Laboratory in Pasadena, examined absorption for a quasar at a redshift of 5.73. Both teams report that the spectra suggest that the reionization epoch began at a redshift of approximately 6.

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