This artist's impression shows a portion of the universe's history.
This artist's impression shows a portion of the universe's history, centered on the "epoch of reionization," a process that ionized most of the material in the cosmos. From left to right: the most ancient light of the universe, the first stars, the reionization process and the first galaxies. Credit: ESA - C. Carreau
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ESA's Planck satellite, a mission with significant participation from NASA, has revealed that the first stars in the universe started forming later than previous observations of the cosmic microwave background indicated. The background is the most ancient light in the history of the cosmos, dating back to 380,000 years after the big bang.

This new analysis also shows that these stars were the only sources needed to clear the "opaque fog" that blocked ultraviolet light from traveling far. As these first stars came to life, their light split neutral atoms apart, making the universe transparent to ultraviolet light. Scientists refer to this as the "epoch of reionization." Planck data show this was a quick process, which was half-complete when the universe had reached an age of 700 million years.

"Thanks to better measurements with Planck, we're confident that reionization occurred later than previous, less precise measurements indicated. That's exciting for scientists because the stars we already know about fit that timeline," said Charles Lawrence, the U.S. project scientist for the mission at NASA's Jet Propulsion Laboratory in Pasadena, California.

Full details from the European Space Agency

News Media Contact

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.

Jan Tauber
ESA Planck Project Scientist
Scientific Support Office
Directorate of Science
European Space Agency
Phone: +31-71-565-5342

Jean-Loup Puget
Principal Investigator, High Frequency Instrument
Institut d'Astrophysique Spatiale
Orsay, France
Phone: +33-169858665

Matthieu Tristram
Laboratoire de l'Accélérateur Linéaire
Université Paris-Sud 11
Orsay, France
Phone : +33 (0)1 64 46 83 88

Written by Claudia Mignone, ESA Science Writer