Life Cycle of Stars
Understand the basics of a star's life cycle: stars are born in clouds of gas and dust (nebulae), shine for millions or billions of years by fusing hydrogen, and eventually die. Massive stars explode as supernovae while smaller stars fade into white dwarfs
What a learner can do afterwards
- Describe that stars form from clouds of gas and dust called nebulae
- State that stars produce energy by fusing hydrogen into helium in their cores
- Explain that massive stars end in a supernova explosion while smaller stars shrink to become white dwarfs
1 · Read
You already know the Sun is a star. Every star has a life story, just like the Sun does: it is born, it shines for a very long time, and one day it changes into something else.
Stars are born inside huge clouds of gas and dust floating in space. We call these clouds nebulae. Gravity slowly pulls the gas and dust into a tighter ball. When the center gets hot enough, a new star switches on.
Deep inside a young star, hydrogen atoms are packed together so tightly and so hot that they fuse into helium. This fusion releases huge amounts of energy, and that is what makes the star shine. It is happening inside the Sun right now.
Not every star ends the same way. A star much bigger than the Sun ends in a huge explosion called a supernova. A smaller star, like the Sun, shrinks down into a small, dim leftover called a white dwarf.
Stars are born in nebulae, shine for a very long time by fusing hydrogen into helium, and end either as a supernova or as a white dwarf.
More to read
Lives of Stars
Stars are born in cold, dark clouds of gas and dust called nebulae. Gravity pulls the material together until the center gets hot enough for fusion. A star spends most of its life steadily burning hydrogen into helium. This is the main sequence. Our Sun is in this phase right now. When the hydrogen runs out, the core shrinks and heats up. The outer layers swell and cool. The star becomes a red giant. What happens next depends on mass. Small stars like the Sun gently shed their outer layers and leave behind a white dwarf. Massive stars end in a violent supernova explosion, leaving a neutron star or black hole.
How Was Our Solar System Formed?
Our Sun and planets formed together from a giant molecular cloud about 4.6 billion years ago. A nearby supernova may have triggered the collapse. As the cloud spun and flattened, the Sun formed in the center. The remaining disk of gas and dust built the planets. The Sun is a typical main-sequence star. It will shine steadily for about 10 billion years total. In about 5 billion more years, it will swell into a red giant, possibly swallowing Mercury and Venus. Then it will shed its layers and become a white dwarf.
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Where it sits
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Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.