In partnership with The Conversation, #Trending brings you Curious Kids, a series where we ask experts to answer questions from kids.
How are stars made? – Zali, age 8, Karkoo, South Australia
Orsola de Marco, astrophysicist, Macquarie University:
"How are stars made? Well, they come into existence because of a powerful force of nature called gravity.
Galaxies are where new stars are born. In galaxies there are very large and fluffy clouds of gas and dust called nebulae.
Gravity makes clumps inside these fluffy clouds – like raisins in a cake. When one of these clumps starts to get tightly compacted and squished together, we say its density goes up. Density means how tightly something is compacted or squished together.
These dense clumps of gas also get hotter and hotter in the centre. When the gas in the centre of a clump reaches a certain temperature (millions of degrees), something quite special starts happening inside the clump: hydrogen atoms come together to form helium.
When hydrogen atoms come together to form helium, it’s called nuclear fusion. This process releases a lot of energy. And this is how a star begins its life.
Just like us, stars are born, they live and then they die. Curiously, the length of a star’s life depends on its birth weight. Light, low-mass stars live very, very long lives.
Our sun is actually a star. It is about 4.5 billion years old and is in the middle of its life. In another five billion years it will get much bigger but then it will start to shrivel.
After that, it will die. Its nuclear power source will switch off and it will just sit there, cooling, like a burnt-out piece of charcoal on a braai.
Stars that are many times heavier than our sun live much shorter lives. The most massive stars live for only a million years or so. Their deaths are much more spectacular than the quiet shrivelling of sun-type stars. They go out in a bang. Scientists call them “supernovae”.
Have you ever heard the saying: “We are all made of stardust?” It’s true. Inside a star, helium atoms combine to make carbon, which is at the root of chemicals that you and all living things are made of.
- To read more of Orsola’s answer, go to the conversation.com
TALK TO US
Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send it to africa-curiouskids@theconversation.com. Please tell us your name, age and which city you live in.