First stars born later than thought

Planck pinpoints end of cosmological dark ages

Polarization of the cosmic microwave

FIRST LIGHT   Light from the cosmic microwave background (coloring shows temperature differences) becomes aligned along certain directions, shown as swirling patterns, as it scatters off electrons in the early universe.

Planck Collaboration/ESA

The first stars in the universe came on the scene a little later than previously thought.

New results from Planck, a satellite that mapped light from the early universe, pinpoint the start of reionization, an era when starlight became powerful enough to strip electrons from hydrogen atoms throughout the universe. Stars triggered the cosmological makeover about 13.25 billion years ago, a mere 550 million years after the Big Bang, researchers report online February 5 at  

Previous results from the WMAP satellite suggested that reionization began about 100 million years earlier, but galaxies from that epoch don’t seem to have enough stars to ionize hydrogen. The delayed start implied by Planck means galaxies had a little more time to build the stars that they needed to drive reionization.

From 2009 to 2013, Planck mapped the cosmic microwave background, or CMB, the first light released into the cosmos, 380,000 years after the Big Bang. The light traveled freely until stars flooded the cosmos with ultraviolet light and ionized hydrogen atoms. Newly liberated electrons left a mark in the alignment, or polarization, of the CMB, which mission scientists analyzed to figure out when the first stars began to shine.

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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