Chuck Bednar for redOrbit.com – Your Universe Online
Polarized light from the earliest days of the universe has revealed that the first stars were formed far later than previously believed, the European Space Agency announced on Thursday.
That revelation comes after the ESA released new high-resolution maps of the sky captured by the Planck satellite between 2009 and 2013. Those new maps, the result of surveys designed to study the ancient light known as the Cosmic Microwave Background, revealed never-before-seen clues about out cosmic history that were encoded in the polarization, the agency explained.
The CMB, which is the light that resulted from a time when the universe was hot and dense (less than 400,000 years after the Big Bang), can currently be seen as microwave wavelengths all over the sky due to the expansion of the universe. Planck’s mission has been to study these emissions, finding the slight differences in density that represent future stars and galaxies.
For the first time, however, ESA Planck project scientist Jan Tauber confirmed that the satellite measured the signal at high resolution across the entire sky, and he and his colleagues found that the first stars formed over 100 million years later than astronomers had previously believed.
We hope the stars aren’t offended because we mistakenly aged them
When the CMB originated in the early universe, the light because polarized as its particles began to bounce off of other particles and vibrate in a specific direction. As the cosmos began to expand and grow cooler, photons and other particles grew farther apart and the collisions become less and less frequent, the ESA researchers explained.
This allowed electrons and proton to finally combine and form neutral atoms without being torn apart by an incoming photon, and also allowed photons to have more room to travel. This made it possible for the light to begin travelling throughout the universe – a journey that continued all the way until today, when it is detected by instruments such as Planck as the CMB.
That light also retains a record of its last encounter with the electrons as part of its polarization, and according to François Bouchet of the Institut d’Astrophysique de Paris, this record “shows minuscule fluctuations from one place to another across the sky” that “reflect the state of the cosmos at the time when light and matter parted company.”
He added that the new data “provides a powerful tool to estimate in a new and independent way parameters such as the age of the Universe, its rate of expansion, and its essential composition of normal matter, dark matter, and dark energy.”
While the polarization data collected by Planck confirms the details of the standard cosmological picture determined through previously obtained measurements of CMB temperature fluctuations, it also sheds led to the realization that stars formed later than experts had long believed.
“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,” explained Marco Bersanelli of Università degli Studi di Milano. “Planck’s observations of the CMB polarization 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,” he added.
Ending the Dark Ages of the night sky
Those “Dark Ages” that Bersanelli refers to, ended as the first stars started to shine. As their light began to interact with gas in the universe, an increasing number of atoms were changed back into electrons and protons. The period in which this occurred is known as the “epoch of reionization,” and during this time electrons were once again able to collide with the light from the CMB.
Although these collisions took place less frequently due to the expansion of the universe, they still left an imprint on the CMB’s polarization, and the new data indicates that the reionization process was complete by the time that the universe was approximately 900 million years old.
Previous studies had indicated that the first stars formed earlier, and that the reionization process would have started roughly 450 million years after the Big Bang. However, images captured by the Hubble Space Telescope provided a census of the earliest known galaxies, some which began to form an estimated 300 million to 400 million years after the Big Bang.
Those galaxies would not have been powerful enough to end the Dark Ages within 450 million years, said George Efstathiou of the University of Cambridge. “In that case, we would have needed additional, more exotic sources of energy to explain the history of reionization.”
The new data solves that problem by pushing back to the start time of the reionization process, in which case the earliest stars and galaxies alone may have been enough to drive it. Also, if the Dark Ages ended later, it means that it could be easier to use future, more powerful observatories (such as the forthcoming James Webb Space Telescope) to detect the very first generation of galaxies, the ESA noted.
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