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First Stars Fired Up 140 Million Years Later Than Previously Thought

A visualization of the polarization of the Cosmic Microwave Background, or CMB, as detected by ESA's Planck satellite over the entire sky.
ESA and the Planck Collaboration
A visualization of the polarization of the Cosmic Microwave Background, or CMB, as detected by ESA's Planck satellite over the entire sky.

It turns out that the "let there be light" moment in the early universe occurred much later than scientists previously thought, according to a newly published analysis of data collected from the European Space Agency's Planck telescope.

The time of the first stars, referred to by astronomers and cosmologists as the "reionization" epoch, is now thought to have occurred about 140 million years later than previously thought, or about 560 million years after the Big Bang, an event that formed our universe 13.8 billion years ago.

"This difference of 140 million years might not seem that significant in the context of the 13.8-billion-year history of the cosmos, but proportionately it's actually a very big change in our understanding of how certain key events progressed at the earliest epochs," said George Efstathiou, one of the leaders of the Planck Science Collaboration.

European Space Agency scientists sifted through four years of data collected by Planck, looking carefully at the Cosmic Microwave Background, or CMB, the faint afterglow of the Big Bang.

"Planck has measured this signal for the first time at high resolution over the entire sky, producing the unique maps released today," explains Jan Tauber, ESA's Planck project scientist.

New Scientist reports: "One of the major findings is that a period called the cosmic dark ages lasted longer than we thought. After the CMB was released, the universe was dominated by a fog of opaque hydrogen gas. It stayed dark for hundreds of millions of years until gravity clumped matter together into the first stars and galaxies, which produced enough radiation to ionise the hydrogen and make it transparent."

The Guardian quotes senior scientist Dr. Carlo Baccigalupi from the International School of Advanced Studies in Trieste, Italy, as saying that the findings could have consequences for the study of dark matter and dark energy.

According to the newspaper:

"The 'dark components' consist of invisible dark matter and dark energy, both of which are still unsolved mysteries whose natures are unknown.

"The scientists, who report their findings in the journal Astronomy and Astrophysics, said more Planck data was still to be analysed, which should provide a clearer picture of the evidence."

Meanwhile, a team of scientists who last year announced evidence for gravitational waves in the early universe after collecting data from the BICEP2experiment in Antarctica, have now withdrawn their claim, according to Nature, concluding that cosmic dust confounded their results. Doubts about the initial conclusion came soon after the March 2014 announcement. NPR's Geoff Brumfiel reported as early as June that the BICEP2 team thought they might be mistaken.

In withdrawing the findings, John Kovac, a principle investigator of BICEP2 at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., said initially the team had "relied on models for Galactic dust emission that were available at the time.

"These seemed to indicate that the region of the sky chosen for our observations had dust polarisation much lower than the detected signal," Kovac said.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Scott Neuman is a reporter and editor, working mainly on breaking news for NPR's digital and radio platforms.

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