Stars
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What powers a star?
A star is ‘powered’ by nuclear
fusion reactions in its core.
Nuclear fusion involves light
atomic nuclei joining together to
form heavier ones. Each fusion
reaction produces a small
amount of energy, but there are
billions of reactions per second.
Each second, the Sun produces 4 × 1026 joules of energy.
It would take 2,000 million nuclear power plants a whole year
to produce the same amount of energy on Earth.
In the Sun, and in most stars, hydrogen atoms fuse together
to form helium. This provides the energy for life on Earth.
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How are elements made?
Nuclear fusion in stars produces
new atoms.
In the early stages of a star’s
life, nuclear fusion mainly
produces light elements such as
helium.
When all the hydrogen has been
used up, other elements are fused
together to make the heavier
elements of the periodic table.
However, not all elements are made in the early stages of
a star’s life. Some of the heavier elements are only made
when a star explodes at the end of its life.
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Heavy elements on Earth
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The life cycle of a star
Every star goes through a life cycle.
A star’s life cycle is determined by its size.
red super
giant
super
nova
red giant
white
dwarf
neutron
star
black
hole
main
sequence
star
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black
dwarf
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How do stars begin and end?
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Life cycle of small stars
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What is a supernova?
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How are black holes formed?
The end of the life cycle of really massive stars is different
to that of massive stars.
After a really massive red giant collapses in a supernova
explosion, it leaves an object so dense that nothing, not
even light, can escape its gravitational pull.
This is called a black hole.
Some scientists believe
that there are black holes
at the centre of galaxies.
If light cannot escape from
a black hole, then how can
a black hole be observed?
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How can a black hole be ‘seen’?
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Life cycle of large stars
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Terms about the life cycle of stars
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Stars life cycle summary
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Glossary
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Anagrams
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Multiple-choice quiz
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