Stellar astronomy

Star formation, fusion, stellar classification, and nucleosynthesis

What is stellar astronomy?

Stellar astronomy is the study of stars — how they form, how they shine, how they change over enormous spans of time, and how they eventually die. Our own Sun is a star, and everything learned about stars elsewhere in the universe helps us understand it too.

How stars shine

A star shines because nuclear fusion is continuously occurring in its core, fusing lighter elements (mostly hydrogen) into heavier ones and releasing enormous amounts of energy in the process (covered in more detail in the Nuclear Physics article). This energy works its way outward from the core and eventually escapes as the light and heat we observe.

Star formation

Stars form from enormous clouds of gas and dust, called nebulae, that slowly collapse under their own gravity. As the collapsing material becomes denser and hotter, it eventually reaches the extreme temperature and pressure needed to ignite nuclear fusion at its center, and a new star is born.

The life of a star

A star spends most of its life in a stable phase, steadily fusing hydrogen into helium. What happens once that hydrogen runs out depends heavily on the star's mass: smaller stars like the Sun swell into a red giant and eventually shed their outer layers, leaving behind a small, dense remnant; much more massive stars end their lives in a dramatic explosion called a supernova, sometimes leaving behind an extraordinarily dense neutron star or a black hole (covered further in the Astrophysics article).

Why stellar astronomy matters

Stellar astronomy explains where the chemical elements that make up planets, and our own bodies, actually came from — nearly every element heavier than hydrogen and helium was forged inside a star at some point in the universe's history. It also gives us the deepest understanding available of our own Sun, the star that makes life on Earth possible.