life cycle of a star

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

II. Size
Larger the star Brighter the Star
Smaller the star Dimmer the Star

III. Distance
Closer the star Brighter the star
Further the star Dimmer the star

Brightness Key Terms
1. Luminosity
2. Apparent Magnitude
3. Absolute Magnitude
4. Parallax

1. Luminosity
Definition- actual or true brightness of a star
Total amount of energy given off
Dependent on 2 things:
Temperature 6000K 10,000K More luminous Size 6000K 6000K More luminous

2. 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
Smaller number equals the brighter the star
Bigger number equals the dimmer the star
Examples are : Sun 28 , Full Moon 11, Polaris 7, Hubble can see +28

3. 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 Expectancy of a Star
Low Mass Star
200 B illion years
Medium Mass Star (our Sun)
10 B illion years
High Mass Star
10 M illion years
The Mass of a star determines the length of it’s life. More Mass = Higher energy used = shorter life.

Life Cycle of a Star
Nebula (low and high mass stars)
Protostar (low and high mass stars)
Main Sequence Star (low and high mass stars)
Red Giant (low mass stars) or Super Red Giant (High Mass stars)
White Dwarf (low mass stars) or Super Nova (high mass stars
Black Dwarf (low mass stars) or Neutron Star (high mass stars)
Black Hole (high mass stars)

All Stars
1. NEBULA 1 st Stage of Life
Ball of gas and dust that is pulled together by gravity.
Gravity pulls cloud INWARD = causes increase of temperature.
2. Protostar when the gases heat up enough to give off light. (still not a star yet )

3. Main Sequence
3 nd Stage of Life Nuclear fusion starts as gas cloud becomes denser and hotter.
The internal heat pressure OUTWARD balances the INWARD gravitational pressure.
Star STOPS collapsing and is STABLE.
Nuclear Fusion  hydrogen atoms fuse into helium
Creates the intense energy found in stars.
Longest stage of Life of Star

Our Sun is in the Main Sequence stage.

Hydrogen fuses into Helium in the Core. 4 H  1 He Creates great heat! E = mc 2

Fate determined by Size
If a normal size star (Sun) follows path 1
If star is a GIANT follows path 2

Path 1
Low/medium mass stars

Low/Medium Mass Star - Sun
4. Red Giant
4 th stage
Main Sequence star expands to become a Red Giant.
Due to shortage of fuel, hydrogen is fusing only in outer shell.
Outward pressure GREATER than Inward pressure = EXPANSION!
Red giant  star that expands and cools.
Due to NO hydrogen in the core.
Core shrinks and atmosphere grows large and cools = turns Red.

The Sun will EXPAND beyond Mars.
Swallowing up the Earth!

Low/Medium Mass Star
5. White Dwarf
Final stage: The Red Giant Collapsed!
Hot and Dim (hot due to collapse)
Inward pressure GREATER than Outward pressure = COLLAPSE
Outer shell escapes into space. (planetary nebula.
Can shine for billions of years before they extinguish.

Low/Medium Mass Star
6. Black Dwarf
The sun cools more and more
Eventually it will become a black mass emitting no light
It will then spend the rest of eternity drifting silently through space

Path 2
High Mass Stars

High Mass Star
Begins from Nebula , evolves into Protostar then into a Massive Mainsequence star.
4. Super Giant Stage :
Expands due to shortage of Hydrogen fuel but because of tremendous heat, fuses heavier elements.
Causes higher heat so expands to larger size = Super Giant
Then runs out of fuel and cools = RED SUPER GIANT

High Mass Star
5. SUPER NOVA
The end is near!
As the Super Giant runs out of fuel . . .
It’s core collapses which causes an EXPLOSION!

Supernova
All the atoms we are made from came originally from these giant supernova explosions.

Super Massive Stars
6. NEUTRON STAR
The core continues to collapse creating a Smaller than Earth
1 teaspoon = 1 billion tons

High Mass Star
7. BLACK HOLE
Final Stage for High Mass Stars
If massive enough, the Neutron star will continue to collapse on itself.

Black Hole  an object that is so massive that light cannot escape its gravity
Remnants of a supernova
Astronomers can detect black holes by using X-ray telescopes

Life Cycle of Star http:// www.youtube.com/watch?v =YU6X3SPZAJo

life cycle of a star

by Bob Smullen

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