What Is a Star? — For Kids
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What Is a Star? — Elementary
The short answer
A star is a big ball of gas.
It gives off heat.
It gives off light, too.
How is a star born?
Stars are born in clouds.
The clouds are made of dust and gas.
The clouds are inside a galaxy.
Gravity pulls the gas together.
Most of the gas is hydrogen.
The cloud starts to spin.
The gas atoms bump into each other.
They bump faster and faster.
That makes heat.
The cloud gets hotter and hotter.
At last, it gets so hot that nuclear fusion happens.
Then the cloud begins to glow.
The glowing cloud is called a protostar.
A star that shines
The protostar keeps growing.
When it stops growing, it has a new name.
It is a main sequence star.
A main sequence star can shine for millions of years.
It can shine for even more than that.
How long it lives depends on how big it is.
Stars change over time.
A star may take millions of years to live out its life.
It may take billions of years.
That is a very, very long time!
How a medium star ends
Some stars are medium size.
In time, nuclear fusion uses up all the fuel.
Then gravity pulls what is left closer together.
The star shrinks.
It may get to be only a few hundred kilometers wide.
Now it is called a white dwarf.
It can stay like this for a long time.
At last, it stops making light at all.
Then it is called a black dwarf.
It will stay that way forever.
Words to know
- Star
- A big ball of gas. It gives off both heat and light.
- Gravity
- The pull that brings gas together into a cloud, and that pulls what is left of a star closer together at the end.
- Nuclear fusion
- What happens when the cloud gets so hot inside that the cloud begins to glow.
- Protostar
- The glowing cloud of gas. It keeps growing.
- Main sequence
- The name for a star when it stops growing. A main sequence star can shine for millions of years or more.
- White dwarf
- What a medium star is called after it shrinks. It may be only a few hundred kilometers wide.
What Is a Star? — Middle
The short answer
A star is a big ball of gas which gives off both heat and light. Stars change over time. It may take millions to billions of years for a star to live out its life. That is a very, very long time!
How stars are born
A galaxy contains clouds of dust and gas, as well as stars. It is in the clouds of dust and gas that stars are born.
As more and more of the gas (which is mostly hydrogen) is pulled together by gravity into a cloud, the cloud starts to spin. The gas atoms start to bump into each other faster and faster. This creates heat energy. The cloud gets hotter and hotter.
Finally, it gets so hot within the cloud that something called “nuclear fusion” happens. The cloud begins to glow.
The glowing cloud of gas is now known as a protostar. The protostar continues to grow. Once it stops growing, it is known as a main sequence star. A main sequence star can shine for millions of years or more. The amount of time it lives is determined by how big it is.
Medium stars
In medium size stars, after the nuclear fusion has used up all the fuel it has, gravity will pull the remaining material closer together. The star will shrink. In fact, it may get to be only a few hundred kilometers wide! The star is then called a “white dwarf”. It can stay like this for a long time.
Eventually, it will stop producing any light at all. It is then called a “black dwarf” and it will stay that way forever.
Massive stars
In large size stars, nuclear fusion will continue until iron is formed. In stars, iron acts like an energy sponge. It soaks up the star's energy. This energy is eventually released in a big explosion called a supernova.
The little bit of matter that used to be at the center of the star before the supernova will then be either a neutron star or a black hole. Which object it becomes depends on the size of the original star.
A star that is 1.5 to 4 times larger than our Sun will become a neutron star. Stars that are even bigger than that will become black holes.
Words to know
- Star
- A big ball of gas which gives off both heat and light.
- Gravity
- The pull that brings gas together into a cloud, and that pulls the remaining material closer together when fusion has used up all the fuel.
- Nuclear fusion
- What happens when it gets so hot within the cloud that the cloud begins to glow. In large stars, fusion continues until iron is formed.
- Protostar
- The glowing cloud of gas. It continues to grow until it stops growing.
- Main sequence
- The stage after a protostar stops growing. A main sequence star can shine for millions of years or more, and how long it lives is determined by how big it is.
- White dwarf
- What a medium star becomes after it shrinks to only a few hundred kilometers wide. In time it stops producing any light at all and becomes a black dwarf.
- Supernova
- A big explosion. It happens in a large star when energy soaked up by iron is eventually released.
- Neutron star
- What the matter at the center of the star can become after a supernova, if the original star was 1.5 to 4 times larger than our Sun.
- Black hole
- What the matter at the center of the star can become after a supernova, if the original star was even bigger than that.
Sources
This page was built only from this source, read in full:
NASA StarChild — “Stars” Level 1 — https://starchild.gsfc.nasa.gov/docs/StarChild/universe_level1/stars.html
Checked November 2, 2026.