Download Neutron star - SharpSchool

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
Red Super Giant

The outer shell
begins to
expand, cools,
and glows red
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

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
Stephen Hawking - Supernova
Supernova
Famous Supernova Remnant Crab Nebula
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
Naked Science

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
Spaghettification
 They must be detected by the x-rays which are given off
 The Largest Black Holes in the Universe
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
Stars: Life and Death
BBC - Describe Stars
Life Cycle Animation -