Stars Star field taken with Hubble Space Telescope
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HertzsprungRussell diagram
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Pleiades
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Star Massive, luminous ball of plasmaplasma Held together by
gravity Shines due to thermonuclear fusion of hydrogen in its
corethermonuclear fusion
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Betelgeuse
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Spectra of stars Allow astronomers to determine a stars:
Composition Luminosity Velocity Mass
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Spectrum of the Sun
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3 types of spectra
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1.Continuous- produced by a glowing body 2. Absorption line
(dark line)- produced when a cooler gas lies between observer and
glowing body this is the type used to ID stars 3.Emission line
(bright line)- emission from a glowing gas, used to study
nebulae
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Star classification Stars are all made of the same material
Spectral differences are due to temperature
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Coolest stars are red, hottest stars are blue
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Classification system O B A F G K M O hottest M coolest
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H R (Hertzsprung Russell) Diagrams Stars plotted according to:
1.Luminosity (absolute magnitude) brightest stars at the top
2.Temperature (spectral class) hotter stars to the left
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H R Diagram (cont.) 1.Main sequence Band from hot (blue) to
cool (red) 90% of stars e.g. the Sun 2.Giants Luminous and cool
10-100x size of the Sun e.g. Aldebaran in Taurus
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3.Super Giants 1000x larger than the Sun e.g. Betelguese in
Orion Antares in Scorpius
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4.White Dwarfs Very hot, but low luminosity due to small size
e.g. Sirius B NO fusion in core, glow due to contraction?
Gravitational forces
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Binary star http://www.astronomy.ohio-
state.edu/~pogge/TeachRes/Movies162/#spbin
http://www.astronomy.ohio-
state.edu/~pogge/TeachRes/Movies162/#spbin
http://www.calvin.edu/~lmolnar/anim/algol.html
Stellar Evolution Stars do not live forever Eventually nuclear
fuel runs out and star dies
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Stages of Stellar Evolution 1.Pre-main sequence Stars form in a
dense, cool cloud of dust and gas Gravitational attraction causes
it to start to glow NO fusion yet Protostar
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Once fusion starts the star enters the main sequence
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Types of stars
http://cas.sdss.org/dr6/en/proj/basic/spectraltypes/
http://cas.sdss.org/dr6/en/proj/advanced/spectraltyp es/
Stages of Stellar Evolution (cont.) The Main Sequence Once
fusion starts the star enters the main sequence The more massive
the star the faster this process Our Sun took about 50 million
years to form
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Stages of Stellar Evolution (cont.) Main Sequence (cont.) When
the force of gravity balances the pressure force the star becomes a
stable main sequence star Hydrostatic equilibrium
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Stages of Stellar Evolution (cont.) Main sequence (cont.)
Higher temp greater luminosity shorter life span Our Sun will fuse
hydrogen (burn) for about 10 billion years
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Stages of Stellar Evolution (cont.) Post-Main sequence Hydrogen
core starts to run out contraction heats up outer shell hydrogen
fusion increases Red Giant Star
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Stages of Stellar Evolution (cont.) Low mass stars (e.g. the
Sun) Red Giant Stars High mass stars (e.g. Betelguese) Super Giant
stars
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Stages of Stellar Evolution (cont.) Death of a star 4 solar
masses or less Contraction of core heats up outer layer expands
ejected into space Planetary Nebula core becomes white dwarf
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Stages of Stellar Evolution (cont.) Death of a star More than 4
solar masses Core contraction causes fusion up to iron rapid
contraction of core rebound and tremendous expansion and shock wave
that blows apart star Supernova
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Stages of Stellar Evolution (cont.) Supernova Outshines all the
other stars in the galaxy combined Nucleosynthesis of elements
heavier than iron
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Stages of Stellar Evolution (cont.) 5-10 solar mass star
neutron star (a paper clip worth of a neutron star would weigh more
than Mt. Everest Emit strong radio waves Pulsar
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Stages of Stellar Evolution (cont.) Stars of 10 solar masses or
more may become a black hole Mass is squeezed into a singularity
Area that sparates a black hole from the surrounding space is the
event horizon