How Are Stars Formed? Formation, Cycles & Lifespan

Last Updated on Mar 14 2024

According to NASA,¹ stars are born within dense clouds of dust and scattered throughout galaxies. The accumulation of gas and dust collapses because of gravity, forming stars. These dense clouds are known as “stellar nurseries” or “star-forming regions.”

Star formation is more complex than that, taking millions of years from start to finish. Though we can’t observe the entire process, the lifecycle of the star is integral to astronomy.

Star Formation

Stars form in nebulae,² or huge clouds of gas and dust. A familiar nebula is the Orion Nebula. Turbulence in the nebula creates sufficient mass, and the gas and dust collapse under their own gravity, creating a buildup of heat in the center. This hot core is the start of the star or a protostar.

Not all of the material in the cloud becomes a star. Some material spreads out and can become planets, asteroids, or comets. Or it could simply remain as dust in the universe.

Computer models of star formation show that the nebulae may divide into multiple sections, which is why stars tend to form in clusters instead of individually.

Star Lifespan and Death

In general, the larger a star is, the shorter its lifespan. Most stars live for billions of years, however.

Once a star uses all the hydrogen at its core, nuclear reactions stop. Without the energy production necessary to support it, the core collapses onto itself and heats up. Hydrogen is still present around the star, so the hydrogen fusion process continues in the surroundings. The hot core pushes the outer layers of the star further outward, leading to an expanding and cooling process that transforms it into a red giant.

Massive stars have comparably massive cores. When they collapse, they could create enough heat to produce nuclear reactions that consume helium and produce heavier elements. This process is temporary and the star’s core will become unstable, either burning stronger or fading. The star then pushes its outer layers and surrounds itself in gas and dust.

The Cycle Begins Anew

The dust and debris left behind by novae and supernovae blend with the surrounding interstellar gas and dust, adding elements produced during stellar death. The materials are recycled, leading to the formation of new stars and planetary systems.

Final Thoughts

Despite all we know about star nurseries, star birth, and their eventual death, there are many unanswered questions. We do know that stars form in nebulae, and they shine for thousands—or even millions of years—but they do die eventually. When that happens, their remains enrich the area and lay the groundwork for a new generation of stars.

Featured Image Credit: Whitelion61, Shutterstock