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Stellar Evolution
Chapter 30.2
Classifying Stars
-H-R diagram- Used to plot surface
temperature and absolute
magnitude (brightness).
-Main-sequence stars- stars that fall
within a band running through the middle of diagram.
(Fig. 1 page 781)
– Cool, red, dim stars – lower right
– Hot, blue, bright stars – upper left
– Cool, red, bright stars – upper right
– Hot, blue, dim stars – lower left
Star Formation
1. Star’s begin as a nebula…cloud of gas
& dust.
-Gas consists mainly of Hydrogen
and Helium.
2. Nebula forms into a Protostar…nebula
begins to flatten into a disk of matter.
Star Formation continued…
3. Nuclear fusion- A star begins to form when
H + H → He; occurs in the core.
-As gravity increases – the rate of fusion
increases.
-As long as fusion is occurring, the star
becomes what we call a main sequence
star.
“Our Sun!”
Star Formation continued…
4. Main Sequence…longest stage in a
star’s life.
-Energy continues to generate in the core
(Fusion of H into He).
-A star in this stage can stay there about 10
billion years.
-When fusion stops, the star will move into
another stage – no longer a main sequence star.
Star Formation continued…
5. Giant and Supergiants- Almost all H
atoms have fused into He atoms.
-a star’s shell of gases grows cooler as it
expands – begins to glow a reddish color.
-they look bright because of their size.
Star Formation continued…the
Final Stages!
6. Energy is exhausted!
-Planetary Nebulas form… a cloud of gas that forms
around a sun-like star that is dying.
-White dwarfs – As the planetary nebula disperses,
gravity causes the remaining matter to collapse inward…what
is left is hot & dense…it is called a white dwarf.
-When a white dwarf no longer gives off light, it forms a
black dwarf.
Star Formation continued…the
Final Stages!
7. Nova - from white dwarfs; large explosions which releases energy &
stellar material into space.
Supernova - from white dwarfs as well; (after super giant stage); a
star that has such a tremendous explosion that it blows itself apart.
-After a supernova the core may contract into a very small but
dense ball of neutrons called a neutron star.
-A neutron star may turn into a Pulsars - a very fast spinning
star that emits pulses of radio & optical energy.
-A supernova may lead to a Black Hole – a star so massive &
dense that even light cannot escape its gravity.