Planck has mapped the delicate polarisation of the CMB across the entire sky
Scientists working on Europe's Planck satellite say the first stars in the Universe lit up later than was previously thought.
The team has made the most precise map of the "oldest light" in the cosmos.
Earlier observations of this radiation had suggested that the first generation of stars burst into life about 420 million years after the Big Bang.
The new Planck data now indicates they fired up around 560 million years after the Universe got going.
"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 Prof George Efstathiou, one of the leaders of the Planck Science Collaboration.
The assessment is based on studies of the "afterglow" of the Big Bang, the ancient light called the Cosmic Microwave Background (CMB), which still washes over the Earth today.