Transcript Stellar Life Stages

Stellar Life Stages
Star Birth and Death
Background info.
• Since early human history, people
have looked up at the night sky in
amazement.
• What is out there?
• What are stars?
• What are planets?
Background info.
• Ancient civilizations imagined that
groups of stars formed pictures
called constellations.
• Many constellations are named
after animals or mythological
characters.
Background info.
Orion, The Hunter
Background info...
Astronomers
recognize 88
constellations
Birth of a Star
•stars are born in a nebula
•a nebula is a dark, cool cloud of dust
and gas
•our galaxy has mostly hydrogen and a
little helium gas
Horsehead is a
dark nebula in
front of the pink
emission nebula.
Horsehead is
about 1,600
light years away.
•nebula becomes dense (thick and
heavy) and starts to contract
•gravity squeezes dust particles to the
center, gravitational energy changes
into heat energy
Contracting
Nebula
draw this
HOT
Protostar
(developing)
•gravity squeezes for millions of years
and temperature slowly rises
•when its hot enough it emits red light
•still too cool for nuclear fusion...
Protostar
•contraction continues and the core
reaches up to 10 million Kelvins
•pressure in the core is high enough
for nuclear fusion to start and a star is
born
•nuclear fusion: when atomic nuclei
join together to form a heavier
nucleus, energy is released, aka
nucleosynthesis
Nuclear Fusion
draw this
the sun
the atomic bomb
•heat from hydrogen fusion causes gas
pressure inside the star to increase
Gas molecules are always
moving in random directions.
What happens to them when
gravity pushes down?
What happens when the temp.
increases?
•when pressure inside balances with
pressure outside, it is called a mainsequence star
Main Sequence
Star
Gravity
draw
this
Gas
Pressure
Balance of
two forces
Main-Sequence Star
•hydrogen fusion continues for
billions of years until it runs out of
hydrogen
•stable stars like our sun will burn
hydrogen for about 10 billion years
•our sun is about 5 billion years old
Main Sequence Stars
Red Giants
•hydrogen fusion in the core ends and
the core contracts (gravity)
•hydrogen fusion still occurs in the
outer layers and they expand
•surface temp. cools and turns red but
the core stays hot and changes helium
into carbon (nucleosynthesis!!!)
Red Giant
Burnout and Death
•all stars eventually run out of fuel and
collapse
•low-mass stars and medium mass stars
use up their hydrogen and collapse
into a white dwarf
...the fate of a
star depends on
its mass
Massive Death
•massive stars explode in a supernova,
debris is ejected as
stardust...eventually gravity pushes it
in
•dying stars that use up hydrogen
produce helium (fusion), over time
helium fuses to become heavier
elements like lithium through iron
(nucleosynthesis)
•black holes are remains of massive
stars that have exploded, they are hot,
dense and have strong gravity
•when matter is pulled into it, the
matter disappears forever
Bend light around them
Not even light can escape
Stellar Evolution
(look at page 710)
60 second summary
Review #1 Where are
stars born?
• nova
• nebula
• nuclear fusion
• hollywood
๏nebula
Review #2 What
happens to a nebula?
• gravity pushes out and it gets cold
• gravity only pushes out
• gravity pushes in and it gets hot
• gravity only pushes in
๏gravity pushes in and it gets hot
Review #3 When a
nebula is hot and enough
pressure is present, what
happens next?
• nuclear combustion
• nuclear fission
• nuclear fusion
• nuclear expansion
๏nuclear fusion
Review #4 What type
of star is our sun?
• protostar
• main sequence star
• red giant
• white dwarf
๏main sequence star
Review #5What is the
next life stage for the
sun?
•nebula
•nova
•red giant
•black hole
๏red giant
Review #6 How do
massive stars die?
• in a nova or supernova
• in a nebula
• in a circle
• in a pulsar
๏in a nova