Download Chapter 15 Section 3

Chapter 15 Section 3
Lives of Stars
The Lives of Stars
• All stars begin their lives as part of nebula.
Nebula is a large dust and gas spread out
in an immense volume. Protostar is the
earliest stage of a star’s life, before
nuclear fusion has begun.
• A star is born when the contracting gas
and dust from a nebula become so dense
and hot that nuclear fusion starts.
• How long a star lives depends on its mass.
Death of Stars
• After a star runs out of fuel, it becomes a
white dwarf, a neutron star, or a black
hole.
• Low-mass or Medium-mass stars when
they run out of fuel, their outer layer
expands and they become red giants, their
outer layer starts glowing and they
become planetary nebula.
• When the core of the original star
gradually cools it becomes a white dwarf,
white dwarfs are about the size of the
Earth with one million times as dense as
the sun.
• High mass stars become supergiants,
when supergiants run out of fuel they may
explode suddenly this explosion is called
supernova.
• Neutron Stars are the remains of high
mass stars, they may contain three times
the mass of the sun in about 25 kilometer
diameter.
• Pulsars are spinning neutron star.
• Black Holes are the remains of the most
massive stars, those that have 40 times
the mass of the sun. The gravity of the
black hole is so great that no light or any
form of radiation can get out of a black
hole.