Telescope study sharpens estimate of helium made after the Big Bang

Astronomers have made the most precise estimate yet of the helium created in the universe’s first minutes, using observations of 15 small galaxies whose chemical makeup has changed little over time. The result cuts the uncertainty surrounding the measurement to 0.5%, about a third of the previous level, according to reporting by SciTechDaily.

The international team’s findings are based on 130 hours of observations with the Large Binocular Telescope. Scientists used the data to study helium and hydrogen in galaxies that preserve a relatively direct record of conditions in the young universe. Researchers at the University of Minnesota Twin Cities were among those involved.

The work appears across five papers in The Astrophysical Journal. It gives physicists a more demanding test of theories about the universe’s beginnings and about the particles and forces described by the Standard Model.

Looking for an early cosmic record

Helium is the second-lightest chemical element and one of the principal products expected from the universe’s earliest stages. The amount present today contains information about the period when the cosmos was only a few minutes old, shortly after its expansion began from an extremely hot, dense state.

For many years, astronomers have estimated the original helium level indirectly. They observed a broad collection of galaxies, compared their helium content with other indicators of chemical change, and projected the pattern back toward a point where few heavier elements were present. That process, known as extrapolation, depends on how reliably the trend can be extended beyond the observations.

The new study instead focused on some of the least chemically evolved galaxies known. Because these systems have accumulated fewer elements over their histories, their gas is closer to the composition left by the early universe. This allowed the researchers to rely less heavily on a calculated starting point and more on measurements from objects that retain a comparatively primitive chemical signature.

The approach does not eliminate the need for careful analysis. At the precision sought by the team, even small influences that systematically push a result away from the true value become important. Earlier studies had treated several such effects as too minor to affect the overall conclusion. Once the target uncertainty fell below 1%, the team had to model them explicitly.

Reading the galaxies’ light

The observations used spectrographs developed at Ohio State University. These instruments spread each galaxy’s light into wavelengths, exposing spectral lines associated with particular elements. The lines provide the information needed to determine the relative amounts of helium and hydrogen in the observed gas.

Rather than relying on a single feature, the researchers examined more than 10 helium lines and 15 hydrogen lines at the same time. Comparing the lines together helped them identify and correct for systematic effects that could otherwise distort the abundance estimate.

Richard Pogge, an Ohio State astronomy professor, said the MODS spectrographs took 12 years to develop before reaching the telescope. Their successful use in this project, he said, demonstrated the purpose of building instruments capable of making fundamental measurements.

Evan Skillman, a University of Minnesota physics and astronomy professor, said the team had set a goal of reaching half-percent uncertainty and achieved it. The result represents a substantial improvement in precision, rather than simply adding another estimate to an existing range.

A test of cosmic history and particle physics

The abundance of light elements is one of three major types of evidence for the Big Bang account of cosmic history. The other two highlighted in the report are the continuing expansion of the universe and the cosmic microwave background, the remnant radiation from its early period. Helium has been studied less extensively than those other two signals, making a more accurate abundance measurement especially useful.

Helium can also be compared with predictions from the Standard Model, the framework physicists use to describe elementary particles and their interactions. A disagreement between the measured abundance and the expected value could point toward missing ingredients in that framework, while agreement would place tighter limits on possible alternatives.

The team used its helium result to calculate how many families of neutrinos were present in the early universe. Neutrinos are extremely light subatomic particles, and their early population affects the conditions under which the first light elements formed. That calculation links observations of nearby galaxies with the particle content of the cosmos when it was only minutes old.

The project’s methodology paper was published on 9 September 2026. Its authors include scientists from the University of Minnesota, Ohio State University and other institutions. By combining unusually primitive galaxies, long telescope observations and detailed treatment of multiple spectral lines, the study turns a measurement of an element into a sharper probe of both the universe’s origin and the physics governing it.