Helium

Helium, the second most abundant element in the universe, possesses astronomical importance that spans various cosmic phenomena. Comprising approximately 24% of the elemental mass in the universe, helium, like hydrogen, emerged during the early stages of the universe, synthesized during the Big Bang nucleosynthesis. Although present in smaller quantities compared to hydrogen, its cosmic abundance remains significant, contributing substantially to the makeup of the cosmos.

Stars

Within the hearts of stars, helium's role in stellar nucleosynthesis is fundamental. Through nuclear fusion processes occurring in stellar cores, hydrogen transmutes into helium via mechanisms such as the proton-proton chain or the CNO cycle. This fusion reaction generates immense energy that fuels stars, sustaining their luminosity and powering their existence.

Stellar Fuel

As stars evolve, helium becomes increasingly integral to their life cycles. In more massive stars, once the hydrogen fuel in their cores is depleted, helium fusion becomes prevalent. The fusion of helium into heavier elements like carbon and oxygen marks a pivotal phase in stellar evolution, leading to the formation of heavier elements and influencing the fate of these celestial bodies.

Observations

Astronomers detect helium's presence in various celestial objects and regions through spectroscopy. Helium emits distinct spectral lines when excited, aiding astronomers in identifying its existence in stars, galaxies, and interstellar space. These spectral signatures provide critical insights into the chemical composition, temperature, and physical characteristics of cosmic entities.

ISM

Furthermore, helium contributes to the composition of the interstellar medium (ISM), existing in different states such as ionized helium (He II) and neutral helium (He I). Its presence within interstellar gas clouds influences the dynamics of star formation, playing a role in the birth and evolution of new stars and planetary systems.

CMB

In the context of the universe's early history, helium's presence during the formation of the cosmos influenced the density and expansion of the early universe. Its effects and interactions during this epoch left imprints on the Cosmic Microwave Background radiation—a critical source of evidence that aids scientists in understanding the origins and evolution of the universe.