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Formation of Stars
What is a star?
1. A sphere of hot, glowing gas.
2. Created inside of Nebulae
1.
The Rosetta
Nebula
Nebulae – A cloud of gas and dust formed in space
3. Stars form when the dust starts to clump and have
gravity
4. When the clump gets large enough and the heat within
the mass reaches 10 million degrees K nuclear fusion
begins
1) Nuclear Fusion – Small atoms, under tremendous pressure and
temperature are able to form larger atoms and releases light
and heat.
How is a star different than a planet?
1. Planets form in a similar fashion to stars
2. Any object that has a mass that is less than 10% of our
sun’s mass will not create enough heat to start nuclear
fusion
3. Our sun is used to determine masses of stars
◦ 1.0 solar mass = mass of our sun
◦ If a stellar object is less than .01 solar mass it will not turn into a
star
Not all stars are created equal
There are 7 different classes of stars
1. O – Hottest stars (30 – 60,000 K), typically blue in color and
very large
2. B – Blue – white in color
3. A – White in color
4. F – Yellow-white color
5. G – Yellow in color, our sun is a G-class star (5-6000 K)
6. K – Yellow - Orange
7. M – Coolest stars (>3500 K) and are typically red and small
Star Life Cycle
1. The life cycle of a star will vary based on it’s class
2. In general the larger and hotter the star the shorter the
it’s life span
3. Our sun is a medium sized star and it will live for
approximately 6 billion MORE years (for a total of 13
billion years)
Stages of the Life Cycle
1. “Childhood of a Star”
1. Protostar – all stars go through this, and is the stage prior to nuclear fusion
starting
2. “Adult stage of a star”
1. Main Sequence Stage – All stars experience this stage.
1.
Longest stage for all stars
3. “Senior Citizen Stages of a Star” – These will vary depending on the size
of the star.
1. Large Mass stars (Classes O, B, A and F) have more violent later life stages
2. Medium Mass stars (Classes G and K) are less violent
3. Small Mass stars (Class M) burn out quietly
“Senior Citizen Stars”
1. Large Mass Stars
1. Super Red Giant Stage  First stage of old age for large stars
1.
Stars will more than double in size, will start to become cooler
2. Supernova Final stage of large stars
1.
After Supernova star either becomes a blackhole OR a neutron star
2. Medium Mass Stars
1. Red Giant Stage  Similar to Super Red Giants but not as extreme
2. White Dwarf  Final stage of stars life, no fuel left for nuclear fusion to
occur
3. Small Mass Stars
1. White Dwarf  Never had enough fuel to become a Red Giant, moves
directly to White Dwarf stage