Download Life Cycle of a Star

Star Light, Star Bright
3 Factors that determine the brightness
of a star
Temperature
Hotter the star
the brighter the star
Blue…..white……..yellow…….orange…….….red
HOTTEST----------------------------------------------COOLEST
Size
• Larger the star
Brighter the Star
• Smaller the star
Dimmer the Star
Distance
• Closer the star
Brighter the star
• Further the star
Dimmer the star
Brightness Key Terms
• Luminosity
– How much light energy is coming from the surface
• Apparent Magnitude
– How bright it appears to be due to distance
• Absolute Magnitude
– How bright it is if its distance was a parsec or 33 light years
• Parallax
– The shift of closer stars against a background of farther stars as
the Earth goes around the Sun
Luminosity
• Definition- actual or true brightness of a star
• Total amount of energy given off
• Dependent on 2 things:
Temperature
Size
6000K
6000K
6000K
10,000K
More luminous since more
energy
More luminous since
more surface area
Apparent Magnitude
• Definition- how bright a star appears when seen from
earth
• System developed where a number is assigned to a star
based on brightness
– Scale is basically based on powers of 10 difference
– A +2 is 10 times as bright as a 3, +100 times as bright as a +4
• Smaller #
Bigger #
Brighter the star
Dimmer the star
• Sun -28 , Full Moon -11, Polaris 7
• Hubble can see +28
Absolute Magnitude
• Definition- brightness of a star as if all
stars were seen from the same distance
Earth
Earth
Sun- average star, Abs. Mag of +4.8 (less luminous, looks brighter because closer)
Rigel- orion, Abs, Mag. of -6.4 (more luminous, further away)
To Determine: apparent magnitude and distance to earth
Moving Stars?
• Parallax- the apparent change in position
of a star due to the movement of observer
Finger: left/right
Life Cycle of a Star
Life Cycle of Stars
Red giant
1
Planetary
White
Nebula
Dwarf
Main
Nebula
Protostar
Sequence
Star
2
Red
supergiant
Supernova
Black Hole
Neutron
Star
Life Cycle Introduction
• http://www.youtube.com/watch?v=f_KLOF
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• http://www.youtube.com/watch?v=YU6X3
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Step 1: Initiation
• Stars are born in
nebulae (huge clouds
of gas and dust)
• Nebula begin to
condense when an
outside force, such as
shock wave, acts
upon it
Step 2: Pre-star
• A protostar forms
when a part of the
nebula contracts,
shrinks, and
pressure and internal
temperature
increases
• Protostar begins to
glow where nebula is
contracting
Step 2 contd: A star is born
• As contraction,
temperature, density, and
pressure increase
protostar gets larger and
brighter
• Center becomes so hot
fusion begins
• Once fusion begins,
a star is born
• TRUE STAR
Step 3: Teenager star
• Internal temperature
hot enough to start
fusion at center said to
be a main sequence
star
• Sun is an example
• Each protostar will turn
into one main
sequence star
• 90% of stars are main
sequence stars
• Vary in surface
temperature and
absolute magnitude
Fate determined by Size
• If a normal size star (Sun) follows path 1
• If star is a GIANT follows path 2
Path 1
Step 4: Middle-aged star
• Red giant- very bright,
once an average star, but
is now close to end of life
- Has expanded to many
times its original size
(heat causes it to expand)
- Hydrogen core has
turned to helium and
eventually to carbon
- Our sun will become a
red giant star in about 5
billion years
Star like our sun begins to die
• Star begins to die when its
core temperature rises to a
point where fuel is used up
• A carbon-oxygen core forms
• Eventually the gases at a
star’s surface begin to blow
away in abrupt bursts
• Resulting glowing halo is
called a planetary nebula
Death of a star like our sun
• atoms no longer fuse, fuel is used up
- Outer gases escape
leaving the core which
collapses and shrinks
- Heat still present but
will continue to escape
for about a billion of
years
White Dwarf- small, very
dense, hot star at the end of
its life, mostly carbon with
nuclear cores depleted
(about the size of earth but
heavier)
Path 2
Step 4: Middle-aged massive star
• Supergiant- largest
known type of star
- can be as large as our
solar system
- rare but exists
- In a massive star,
hydrogen is fused more
quickly and fusion
continues until a iron
nuclei is formed
Death of a Supergiant
• Elements are used up
very quickly and
eventually runs out of
fuel
• Collapse of the core
produces a shock
wave that blasts the
star’s outer layers into
space producing a
supernova
• Supernova- exploding
star
Option A after a supernova
•
After a massive star
“goes supernova” it
leaves behind its
core (called a
neutron star)
-Neutron Star- small,
dense star made of
neutrons
• When neutron star is
first formed, it spins
very rapidly and gives
off radio waves
Option B after a supernova
• Black Hole- a star that
collapses
• How do we know they
exist? Pulls gases off
nearby stars, as gas
is pulled into this
“nothing space” xrays are emitted from
the gas as molecules
are pulled in
Cycle continues
• Star is born from great clouds of gas
and dust
• Stars mature, grow old, and die
• As a star dies, it makes new clouds
of dust gas and dust where new
stars can begin to form
• More massive a star, the shorter its
life
• http://www.youtube.com/watch?v=HfqcZd
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• http://www.youtube.com/watch?v=hoLvOv
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Hertzsprung-Russell Diagram
• Graph that compares temperature and
absolute magnitude (brightness)
The Hertzsprung-Russell Diagram
(H-R diagram)
Cool and
bright
Bright
Hot and
bright
Hot and
dim
Sun
Cool and
dim
Dim
Hot
Cool
Hot and
bright
Supergiants
Cool
and
bright
Giants
Main sequence
White
Hot and Dwarfs
dim
Cool
and
dim