• UnEarthed

How are stars created?

By: Lilianne Sutton

You might already know that the Sun is a star, but what is a star? How are they made?

Stars are superhot, large spheres of gas. They’re mostly composed of hydrogen and helium, which are the two lightest elements. Hydrogen and helium are also the most abundant elements in the universe! Most of the time they exist as large clouds of gas. These large gas clouds exist in the space between the billions of stars in the universe.

Sometimes, a large amount of dust will accumulate with these clouds of gas and form something called molecular clouds. You might think dust and gas are lightweight, but these molecular clouds can actually be extremely heavy. As in, they weigh up to hundreds of thousands of times more than the Sun, which is hundreds of thousands of times heavier than the Earth! The matter inside the clouds can drift and bounce around throughout the millions of years that they exist and will sometimes collect into large patches where the matter is very close together. These patches can then form their own gravitational pull, attracting even more gas and dust towards them. This gravitational pull will become so strong that the cloud collapses together to form the beginning of a star!

This beginning of the star is called a pre-stellar core (pre meaning before, stellar meaning star!). The core continues to contract and collapse on itself, becoming smaller and smaller over approximately 50,000 years. The pre-stellar core starts 10,000 AU wide. An AU, or astronomical unit, is the average distance between the Earth and the Sun. It shrinks to be a large disk of gas around a central core of denser gas and dust, approximately 1000 AU wide. At this stage, the system has an axis that the star spins around, like Earth! The pre-stellar core has now become a proto-star. Proto means first, or early; so, a proto-star means it’s an early-star.

In the next stage of star development, most matter in the disk either joins the central core of the star or is expelled away. This occurs over approximately 1000 years. There is enough matter packed into the central core that the star begins the nuclear reaction, where hydrogen reacts to form helium. The nuclear reactions in the star cause the star to shine, like the Sun. This stage of the star is called a T-tauri star!

The star and the star system continue to develop over the next several million years. The material that was expelled away from the star remains a disk, just further from the star. This matter later becomes planets that orbit the star. Once those planets are formed, the star system is considered a fully mature system! The nuclear reactions within the star will continue for up to 10 billion years. The sunlight we see is the radiation released by those nuclear reactions.

To conclude, stars are created from large clouds of dust and gas over a process that can span a few million years. There are multiple stages in the creation process that have different shapes and sizes. Sunlight is powered by nuclear reactions in which hydrogen becomes helium. Stars shine for up to 10 billion years after becoming full-fledged stars.

So, the next time you’re out on a walk, or looking through the window, look up at the night sky! Now you know how all those stars that shine and twinkle were made.


NASA. (n.d.). Stars. NASA. Retrieved October 18, 2022, from https://science.nasa.gov/astrophysics/focus-areas/how-do-stars-form-and-evolve

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