In Simple Terms
In 1925, a young scientist named Cecilia Payne discovered that stars, including our sun, are mostly made of hydrogen and helium. This was a big surprise because people used to think stars were made of the same materials as Earth. Her work changed how we understand the universe, even though it took a while for others to believe her.
Revolutionary Discovery
In 1925, Cecilia Payne, a 24-year-old working at Harvard College Observatory, made groundbreaking calculations showing that stars are primarily composed of hydrogen and helium. This contradicted the then-popular belief that stars had a similar composition to Earth.
Spectral Lines and Misinterpretation
In the early 20th century, scientists relied on spectral lines to identify elements in stars. These lines appear when atoms in a star’s outer layers absorb certain wavelengths of light, leaving unique marks for each element. However, they mistakenly assumed that stronger lines indicated more of an element, which wasn’t always true.
Previous estimates were influenced by the clarity of these lines rather than the actual amount of an element. Scientists thought the sun and Earth were similar because elements common in Earth’s crust showed strong lines in the sun’s spectrum.
The Role of Atomic Physics
Payne used the theory of Indian physicist Meghnad Saha, which links atom ionization with temperature and pressure. Modifications by physicists Ralph Fowler and Edward Milne helped explain why atoms might not appear in spectral lines due to ionization or electron transitions to other energy levels.
Using this theory, Payne demonstrated that the Balmer absorption lines of hydrogen, which appear when an electron is in the first excited state, could indicate a vast amount of hydrogen even if only a small fraction of atoms were in that state.
Challenges and Delayed Recognition
Payne faced significant challenges in getting her results accepted. Prominent astronomer Henry Norris Russell advised her to retract her findings, calling them impossible. However, four years later, Russell’s own results confirmed Payne’s discoveries, proving hydrogen to be the most abundant element in stars.
In his 1929 publication, Russell acknowledged Payne’s correctness and praised her work. Despite this, it took a long time for the scientific community to recognize her fundamental contributions.
Conclusion
Cecilia Payne’s discovery radically changed our understanding of the composition of stars and the universe. She proved that hydrogen and helium are the primary elements in stars, which helped develop models of stellar and cosmic evolution. Despite the challenges she faced, her work remains a pioneering achievement in astronomy.