What are stars really made of?

For thousands of years, humanity has gazed up at the stars in fascination, using them to navigate vast oceans, mark the passage of seasons, and inspire myths, art, and poetry. These celestial lights, scattered across the night sky, seemed mysterious yet constant, their true nature beyond comprehension. Many scientists and astronomers spent much time theorizing about the nature of these far-flung objects, and the early 1900s saw many of these theories debunked by a brilliant young graduate student.

What beliefs did scientists have about the stars a century ago? What are these celestial objects truly made of? And how did a 24-year-old would-be astronomer reveal the secrets of starlight? Click through this gallery to find out.

A new chapter

For thousands of years, stars have served as tools for navigation, inspiration for myths, and sources of wonder. But in 1925, a groundbreaking discovery by a graduate student named Cecilia Payne revealed the true nature of the shimmering points of light in the sky.

A pioneer in astronomy

Payne was a prodigious young scientist whose innovative thinking at the age of 24 reshaped how the universe was understood. Her work challenged long-established ideas and became a crucial step in astrophysical research.

A difference of opinion

While many scientists of the era believed that stars (including our very own Sun) were made of heavy metals similar to the Earth, Payne believed that they had a different chemical makeup altogether. She posited that hydrogen and helium were the primary elements found in stars. But how did she go about proving this?

Overcoming barriers in science

Like any scientific hypothesis that went against the dogma of the time, Payne’s research faced significant skepticism. But as a young woman in the male-dominated field of astronomy, she felt those tensions even more.

Humanity’s first steps

In the 1600s, humanity began constructing telescopes that allowed humans to observe stars more closely. As a result, many observations were made about these points of light, including that they tended to cluster together into cloudlike “nebulas.”

Opening new doors

The 19th-century invention of spectroscopy enabled scientists to break starlight into distinct colors that would then interact with a photographic glass plate coated in an emulsion. When photons of light touched the emulsion, dark marks would appear. These would basically be the signatures of far-away stars.

Early misconceptions

In the 1800s, scientists assumed that stars contained the same materials as Earth because of similarities in spectral patterns on emulsion plates. This belief remained unchallenged until Payne’s work demonstrated the overwhelming abundance of hydrogen and helium in stars.

Mentorship and education

Initially, Payne studied botany, but quickly switched over to physics in her first year. Her education in atomic physics was brought about by Ernest Rutherford (who discovered that every atom has a positively charged nucleus) and Niels Bohr (who explored the behavior of electrons orbiting that nucleus).

Finding opportunity in America

After being denied full academic opportunities in England, Payne moved to the United States in 1923. She began her graduate studies at Harvard College Observatory, one of the few institutions that welcomed women in astronomy, where she made her revolutionary discovery.

Pioneering spectroscopy analysis

Payne rejected her mentor’s suggestions to replicate earlier work and instead analyzed decades of untouched spectroscopic data. At the time, no other institute in the world had as many emulsion plates as Harvard, all of which preserved star signatures.

Light and its behavior

Interestingly, the color of light always corresponds to a specific atom. For example, carbon atoms would always emit or absorb the same amount of light as each other, while it would differ to the atoms of other elements.

Collaborating with Meghnad Saha

Payne integrated the insights of Indian physicist Meghnad Saha (pictured) into the behavior of gases under extreme conditions, enabling her to calculate how temperatures and pressures in stars can affect spectral patterns.

Hydrogen and helium

Payne’s research demonstrated that hydrogen and helium are far more abundant in stars than any heavier element. This finding challenged previous beliefs and reshaped scientists’ understanding of the chemical makeup of the universe.

Resistance from leading astronomers

During Payne’s time, there were many challenges that scientists (especially women) faced whenever they disputed scientific dogma. Despite the brilliance of her thesis, Payne faced strong criticism, particularly from Henry Norris Russell, a prominent astronomer who doubted her findings.

A thesis of enduring relevance

Payne’s 200-page thesis is still regarded as a masterpiece of astronomical research. Its precision, attention to detail, and transformative conclusions have inspired generations of scientists to explore the stars with greater understanding.

A dedicated academic

After earning her doctorate in 1925, Cecilia Payne dedicated her entire academic career to Harvard. As a woman, she was barred from becoming a professor, and so she spent many years in low-paid research jobs despite her overwhelmingly successful thesis.