Ask A Scientist

What are stars made of?

Asked by: Kelsey Feeko
School: West Middle School, Binghamton School District
Grade: 6
Teacher: Jo Ann Summerlee
Hobbies/Interests: Playing "Just Dance 4", walking my dog and hanging with my best friend, Sasha. 
Career Interest: Veterinarian, help kids or take care of premature babies

Answer from Kyle Reeser

Biomedical Engineering Graduate Student, Binghamton University

Research Area: Tissue Engineering
Interests/hobbies: Traveling, language studies, cooking and music

I believe that everyone, at some point in their life, may ask themselves this same question.

The basic units of matter, that which we call elements, comprise everything we see around us. In the wake of the Big Bang, tiny particles were bound together to form the two simplest elements on the periodic table, hydrogen and helium. The first stars after the birth of the universe 13.7 billion years ago were formed from gas clouds containing these elements, collecting and condensing under their own gravity. 

Stars are enormous reactors powered by a process called nuclear fusion – which occurs within their core. Under intense heat and pressure, small atoms are cooked into larger atoms. The result of this process, the forming of heavier elements from lighter elements, is the release of a massive amount of energy. It is the release of this energy that sustains the star, opposing the strong inward force of gravity. 

We experience the products of nuclear fusion within our own star every day, in the form of heat and light. Generally speaking, a small star will only convert hydrogen into helium during its lifespan. A medium-sized star, such as the Earth’s Sun, will then convert helium into carbon and oxygen once its supply of hydrogen has been depleted. And, a massive star will continue to produce heavier elements late in life. The mass of our Sun is approximately 71% hydrogen, 27% helium. The remaining materials are heavier elements that were created in stars that existed long ago.  

When a star’s supply of fuel has been depleted they collapse and then explode, scattering their contents far and wide. These clouds of elements eventually collect and condense, forming the next generation of solar systems.

Let’s not let the beauty of this topic escape us. In life, and in death, stars have produced all of the naturally occurring elements in existence that are heavier than hydrogen. The atoms that make up everything we have ever touched and every person we have ever known are traceable to those little specks of light we see in the nighttime sky. 

So when you look skyward on a clear evening, don’t let the vastness make you feel small; your atoms have a direct connection to the stars! To quote the famous astrophysicist Dr. Neil deGrasse Tyson, "We are part of this universe, we are in this universe, but perhaps more important than both of those facts, is that the universe is within us."

Last Updated: 3/1/17