The latest data from the European Space Agency's Planck space telescope revealed that the earliest known stars in the universe likely appeared 150 million years later than previously believed. The Planck space telescope launched in May 2009. Though the spacecraft’s science mission ended in the fall of 2013, scientists are still sifting through the enormous amount of data collected during those four and a half years about the cosmic microwave background (CMB), which is leftover radiation from the Big Bang that first appeared when the universe was 380,000 years old.
The CMB also provides clues about when the first light visible in the universe appeared, following an event called reionization. The universe was initially completely dark due to heavy, opaque hydrogen that dominated a period suitably known as the cosmic “dark ages.” Reionization effectively cleared this blanket of hydrogen up, allowing photons to move freely. As the earliest stars and galaxies formed and filled the universe with light, the photons helped the hydrogen gas dissipate and revert to free protons and electrons. These particles then began to interact with the CMB, polarizing it. In 2006, data from the Wilkinson Microwave Anisotropy Probe (WMAP) indicated that reionization began 420 million years after the Big Bang. However, the newly released Planck observations don’t corroborate that figure. Instead, it is much more likely that this process occurred when the universe was about 550 million years old.
"After the CMB was released, the universe was still very different from the one we live in today, and it took a long time until the first stars were able to form," astrophysicist Marco Bersanelli of Università degli Studi di Milano, Italy, said in a press release. "Planck's observations of the CMB polarisation now tell us that these 'Dark Ages' ended some 550 million years after the Big Bang—more than 100 million years later than previously thought. While these 100 million years may seem negligible compared to the universe's age of almost 14 billion years, they make a significant difference when it comes to the formation of the first stars."
In addition to correcting the age of the earliest stars in the universe, the Planck data also supported previous results on other topics, including respective amounts of dark energy, dark matter, and ordinary matter throughout the universe.
"These are only a few highlights from the scrutiny of Planck's observations of the CMB polarisation, which is revealing the sky and the Universe in a brand new way,” explained Planck scientist Jan Tauber. "This is an incredibly rich data set and the harvest of discoveries has just begun."