The concentration of helium hydride ions in the universe significantly impacted the process of early star formation.  During this early phase of the universe, simple molecules such as HeH⁺ and H₂ were essential to the formation of the first stars...star dust as described in the image above.

BUT NOT YET... In order for the contracting gas cloud of a protostar to collapse to the point where nuclear fusion can begin, heat must be dissipated. This occurred through collisions that excited atoms and molecules, which then emitted this energy in the form of photons. When the ambient temperature drops below 10,000 degrees Celsius, this is unstable environment for the dominant hydrogen atom. Further cooling can only take place via molecules that can emit additional energy through rotation and vibration. Due to its pronounced dipole moment, the HeH⁺ ion is particularly effective at these low temperatures and has long been considered a potentially important candidate for cooling that led to the formation of the first stars.  

This recombination was followed by the 'dark age' of cosmology: although the universe was now transparent due to the binding of free electrons, there were still no light-emitting objects, such as stars. Several hundred million years passed before the first stars formed.

Astronomers estimate that the universe could contain up to one septillion stars – that is the numeral one followed by 24 zeros. Our Milky Way alone contains more than 100 billion, including our most well-studied star, the Sun.  Stars are giant balls of hot gas – mostly hydrogen, with some helium and small amounts of other elements. Every star has its own life cycle, ranging from a few million to trillions of years, and its properties change as it ages.

Stars form in large clouds of gas and dust called molecular clouds (see image at top of this page). Molecular clouds range from 1,000 to 10 million times the mass of the Sun and can span as much as hundreds of light-years. Molecular clouds are cold which causes gas to clump, creating high-density pockets. Some of these clumps can collide with each other or collect more matter, strengthening their gravitational force as their mass grows. Eventually, gravity causes some of these clumps to collapse. When this happens, friction causes the material to heat up, which eventually leads to the development of a protostar – a baby star.

The first stars in the Universe are believed to have formed only a few hundred million years after the Big Bang. The heated and ionized pristine intergalactic medium, and their supernova explosions, enriched the primordial gas with the first heavy elements; the universe was born with only hydrogen and trace amounts of helium. These stars thus altered in a fundamental way the chemical and thermal state of the gas from which the first galaxies then formed, in turn triggering the first self-sustaining cycle of star formation, feedback, and chemical enrichment. Understanding the formation and properties of the first stars is thus an important step towards a comprehensive picture of structural formation in the early universe.

Stars support the fusion of hydrogen to create helium.  Other elements are formed in stars through nuclear fusion, a process where lighter atomic nuclei merge to form heavier ones under intense heat and pressure. Stellar nucleosynthesis is the process by which stars create heavier elements from lighter ones through nuclear fusion reactions in their cores. This process is responsible for the creation of all elements up to iron and also generates the energy that powers stars. Elements heavier than iron are primarily formed in more explosive events like supernovae and neutron star mergers, through processes known as neutron capture; massive stars create heavier elements which are then scattered into space by supernovae or neutron star mergers.