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Studying the Lives of Stars Stars don’t last forever Each star is born, goes through its life cycle,
and eventually die
Life Cycle of a Star
A Star is Born
A star is made up of a large amount of gas in a relatively small volume
A nebula, is a large amount of gas and dust spread out in in an immense volume
All stars begin their lives as parts of nebulas
Gravity can pull some of the gas and dust in a nebula together and it begins to spin – this is called a stellar nebulla
The contracting cloud is then called a protostar
Protostar – The Earliest Stage A protostar is the earliest stage of a star’s life
A protostar is born when the contracting gas and dust become so hot that nuclear fusion starts
Main Sequence
Once nuclear fusion occurs in the cloud, it will begin to glow brightly
It contracts a little and becomes stable
It is now a main sequence star and shines as nuclear fusion produces heat and light
The star may remain in this stage for millions or billions of years
Red Giant As the main sequence star
glows, hydrogen is converted to helium
When the hydrogen supply begins to run out, the core becomes unstable and contracts
The outer shell starts to expands and glows red as it cools
It is now a red giant Red Giant – expands and glows red as it cools
The outer shell begins to expand, cools, and glows red
Red Super Giant
Medium vs. Massive Stars The amount of mass a star has determines
the path it will take after the red giant phase
Medium Stars – Planetary Nebula At 200,000,000 °C the helium atoms in the core fuse to
form carbon atoms
The last of the hydrogen gas in the outer shell is blown away to form a ring around the core
The ring is a planetary nebula
White Dwarf When all the helium atoms are fused,
the star begins to die In white dwarfs, gravity causes the last of the star’s matter
to collapse inward and compact
It is now a white dwarf
The star’s matter is extremely dense
White dwarfs are the size of Earth, but have the mass of the Sun
Once all the energy is gone, it becomes a black dwarf , which is a star that is dead and no longer emits light
Massive Stars - Supernova
Stephen Hawking - Supernova
Once massive stars reach the red giant phase, the core temperature continues to increase
The energy is eventually released in a powerful explosion called a supernova
Supernova – super giant explodes
The temperature of a supernova can reach 1,000,000,000 °C
Neutron Stars A star that is 1.5 – 4 times as
massive as our sun becomes a neutron star after a supernova
Neutron stars spin rapidly giving off radio waves
Neutron star – core collapses and becomes very dense
If the radio waves are emitted in pulses, they are called pulsars
Black Holes
The most massive stars become black holes when they die
In a black hole, no nuclear fusion is taking place, so it is swallowed by its own gravity making it a black hole
Black holes are not visible
They must be detected by the x-rays which are given off
The Largest Black Holes in the Universe
Naked Science
Spaghettification
Lifetime of Stars
A star’s life cycle is determined by its mass!
The larger the mass, the shorter the life cycle
Small stars use up their fuel more slowly than large stars, so they have much longer lives
Small stars can live up to 200 billion years
Medium stars (like the sun) can live for about 10 billion years
Giant stars usually live for about 10 million years
Checkpoint
If a star is twice as massive as the sun, will it have a longer or shorter life than the sun?
Shorter!
Deaths of Stars
When a star begins to run out of fuel, the center of the star shrinks and the outer part of the star expands
The star becomes a red giant or supergiant
When a star runs out of fuel, it becomes a white dwarf, a neutron star, or a black hole
Life Cycle Animation - classzone
BBC - Describe StarsStars: Life and Death
