The helium in a party balloon is the very gas that makes it float. But long before balloons, helium appeared in the first minutes after the Big Bang. Its exact abundance in the universe is like a fingerprint: it tells you how many kinds of neutrinos (ghostly particles that pass through walls) exist.
Astronomers have found a way to measure this fingerprint more accurately. They look at distant clouds of hot hydrogen that contain almost no heavy elements, such clouds preserve the composition of the early universe. A new method for analyzing spectra obtained with the Large Binocular Telescope in Arizona allows them to determine the helium fraction with an uncertainty of about 2% for each cloud. And by selecting the best clouds, the scientists hope to achieve an overall precision of 0.5%.
Why such precision? The number of neutrino types in the Standard Model of particle physics is three. But if helium measurements point to a different value, that would hint at new physics — for instance, the existence of sterile neutrinos that do not interact with matter. So a precise helium count in ancient gas is a test of the very foundations of our understanding of the world.
as written by the authors arXiv:2601.22232
Extremely low metallicity HII regions have been observed with the goal of determining the primordial helium abundance ($$Y_{\rm p}$$). $$Y_{\rm p}$$, combined with standard big bang nucleosynthesis and the half-life of the neutron, provides a direct measurement of the number of neutrino families, but $$Y_{\rm p}$$ must be measured very precisely to provide meaningful constraints on physics beyond the Standard Model. Here we describe a program to combine new Large Binocular Telescope (LBT) observations with a new analysis methodology to significantly improve the determination of $$Y_{\rm p}$$. The LBT, with its MODS and LUCI instruments, produces spectra, which, when combined with our new analysis methodology, are capable of delivering He abundances in individual HII regions with uncertainties of approximately 2% or less. Archival LBT/MODS spectra of standard stars over a four-year period enable the determination of a wavelength-dependent uncertainty in the MODS spectral response, resulting in improved relative emission line uncertainties. An optimized sample of low-metallicity galaxies has been selected with the goal of producing a determination of $$Y_{\rm p}$$ with a precision of $$\sim$$ 0.5%, sufficient to provide an independent constraint on the effective number of neutrino families of $$\sim$$ 3%.
Helium was first found on the Sun, not on Earth: in 1868, astronomers spotted an unknown line in the solar spectrum and named the element after Helios, the Greek god of the Sun.
In Stanislaw Lem's novel Solaris, the planet's ocean is made of an unknown form of matter; precise measurements of cosmic composition could help distinguish ordinary matter from exotic matter.