More than 13 billion years after the birth of the universe, astronomers have been able to get closer than ever to answering a question that dates back to the very first minutes: How much helium did the universe create after the Big Bang?
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An international team used 130 hours of observations with the Large Binocular Telescope (LBT) at Mount Graham in Arizona, USA, to study 15 gaseous regions extremely poor in heavy elements, and arrived at a measurement of primordial helium with an accuracy of nearly 0.5%, which is about three times better than previous standard.
This result not only tests the history of the first elements, but also gives physicists a precise tool to examine the Standard Model of physics and the number of neutrino families in the early universe.
This type of measurement began decades ago, when scientists realized that the amount of helium left over after the nuclear fusion of the Big Bang bears a direct imprint of the conditions of the nascent universe.
However, the problem is that helium is also formed inside stars, so we must look for regions that haven't undergone significant chemical evolution and then extrapolate their values to approximate the early state of the universe. For this reason, the team chose galaxies and gaseous systems very poor in heavier elements, as they are the closest possible "preserved records" of the early universe.
Galaxies that remained close to the beginnings of the universe
The researchers relied on 15 regions that were extremely poor in heavy elements, within a broader sample of 54 ionized hydrogen regions that the project observed with the telescope, and used two multi-object spectrometers to analyze the emission lines of helium and hydrogen simultaneously.
This allowed for the determination of the gas's physical conditions and the manipulation of small effects that previously seemed insignificant but become crucial when scientists attempt to achieve accuracy below 1%. The team was able to analyze more than 10 helium lines and 15 hydrogen lines in this data.
Helium becomes a particle testing tool
The significance of this measurement goes beyond simply determining the ratio of a chemical element; primordial helium serves as a test case for fundamental physics. Combined with measurements of heavy hydrogen, the cosmic microwave background, and models of nucleosynthesis, researchers have been able to deduce the number of neutrino families that existed in the early universe.
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