New measurements of helium in some of the universe’s most metal-poor galaxies have reduced the uncertainty in estimates of primordial helium from about 2% to nearly 0.5%, giving researchers a more precise test of conditions that existed shortly after the Big Bang and supporting the standard model of particle physics.
The measurement comes from observations made with the Large Binocular Telescope. Researchers examined helium signals in optical and infrared light from metal-poor nebulae, clouds of gas and dust where stars can form.
By using those signals to determine the temperature and density of the gas, the team assembled 48 high-quality galactic samples. The resulting dataset was designed to improve estimates of how much helium existed in the universe before stars began producing additional amounts through nuclear fusion.
About 90% of the universe’s helium formed during the Big Bang, according to the study. The remaining 10% came from stars over the last 13.5 billion years.
The work is part of the LBT Yp project, which aims to determine the amount of primordial helium with enough precision to test ideas about the universe’s earliest conditions.
Helium can test early-universe physics
The amount of primordial helium is linked to the types of neutrinos, tiny subatomic particles, that were likely present when the universe was about one second old.
That makes helium abundance useful for testing models of the early universe. A substantially different helium measurement could have challenged existing ideas about those conditions and potentially pointed toward new physics.
Astronomers cannot directly observe the universe all the way back to its beginning. The earliest light they can see comes from roughly 400,000 years after the Big Bang, when the universe became transparent enough for the cosmic microwave background to form.
The researchers therefore compare measurements from galaxies with archival observations of the cosmic microwave background. This provides a way to test whether current models remain consistent with observations from different stages of cosmic history.
The new measurement agrees with the standard model
Getting a precise result required observations of extremely metal-poor galaxies, including the small galaxy Leo P. The researchers also had to account for effects from Earth’s atmosphere that could influence their measurements.
With the improved helium abundance measurement, the team concluded that the number of neutrino species present at the Big Bang is consistent with the standard model of particle physics.
The researchers say the improved precision also provides stronger constraints on the physics associated with the universe only seconds after its beginning.
The LBT Yp project is continuing its work, with plans to study additional metal-poor galaxies and use large astronomical archives from collaborative projects such as DESI. The researchers expect that exploring more galaxies and applying the techniques developed for this work will take many years.
The study was published in The Astrophysical Journal.
