Stars Star field taken with Hubble Space Telescope

Hertzsprung–Russell diagram

Pleiades

Star Massive, luminous ball of plasmaplasma Held together by gravity Shines due to thermonuclear fusion of hydrogen in its corethermonuclear fusion

Betelgeuse

Spectra of stars Allow astronomers to determine a star’s: Composition Luminosity Velocity Mass

Spectrum of the Sun

3 types of spectra

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

Star classification Stars are all made of the same material Spectral differences are due to temperature

Coolest stars are red, hottest stars are blue

Classification system O B A F G K M O hottest M coolest

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

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 – x size of the Sun – e.g. Aldebaran in Taurus

3.Super Giants – 1000x larger than the Sun – e.g. Betelguese in Orion Antares in Scorpius

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

Binary star state.edu/~pogge/TeachRes/Movies162/#spbin state.edu/~pogge/TeachRes/Movies162/#spbin

Albireo (the Cal star)

Stellar Evolution

Fusion

Carbon-carbon fusion

supernova

m-3114.html

Stellar Evolution Stars do not live forever Eventually nuclear fuel runs out and star dies

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

Once fusion starts the star enters the main sequence

Types of stars es/

ning_of_color/

Stars/magnitude_scale.html

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

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

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

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

Stages of Stellar Evolution (cont.) Low mass stars (e.g. the Sun)  Red Giant Stars High mass stars (e.g. Betelguese)  Super Giant stars

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

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

Stages of Stellar Evolution (cont.) Supernova Outshines all the other stars in the galaxy combined Nucleosynthesis of elements heavier than iron

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

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