Download - Classifying Stars
Classifying StarsClassifying Stars
The Hertzsprung-Russell Diagram (H-R Diagram)– Graph plotting the surface temperatures of stars
against their luminosity (total energy given off each second)
– Diagonal band that goes from upper left to lower right is the MAIN-SEQUENCE STARS
– The Sun is a main sequence star
Classifying Stars continued…Classifying Stars continued…
Supergiants: very luminous, large stars; red supergiants are the largest stars
Giants: highly luminous, large starsDwarfs: small, dim stars
– White dwarfs: very faint, very dense, very small stars
Classifying Stars continued…Classifying Stars continued… Variable stars: vary in brightness over regular cycles
– Pulsating stars: change in brightness as they expand (cool, dim) and contract (hot, bright)
– Cepheid variables: the longer their cycle is the larger their absolute magnitude is
– Eclipsing binary: 2 stars of unequal brightness that revolve around each other and appear to change brightness
Pulsars: emits bursts of radio waves and light– They are neutron stars formed in supernovas– They produce radio pulses because they rotate very rapidly
LT 9: LT 9: I can describe how a protostar becomes a I can describe how a protostar becomes a star.star.
Begins as a nebula (a cloud of dust and gas) Diffuse nebula: lit up by bright light from nearby
star (ex: Great Nebula in Orion) Dark nebula: show up as dark patch (ex: Horsehead
Nebula in Orion
Birthplace of StarsBirthplace of Stars
Making a StarMaking a Star Cloud starts compressing and particles are pulled
closer to each other by gravity and temperature rises
Hot areas start to glow (protostars) and continue contracting
Eventually they contract enough to trigger fusion and hydrogen into helium which gives off huge amounts of energy (star)
When the energy released counterbalances gravity, the star stops contracting (main-sequence star)
LT 10: LT 10: I can explain how a main-sequence star I can explain how a main-sequence star generates energy.generates energy.
Stable StateStable StateNuclear fusion is what fuels a star’s energy
– Hydrogen fuses to Hydrogen to form HeliumWhen Hydrogen in core is used up, gravity
causes the core to collapseTemperature rises making the outer shell of
the star super expandThe surface temperature drops and it is now
a huge, bright, red aging star
LT 11: LT 11: I can describe the evolution of a star after I can describe the evolution of a star after is main-sequence stage.is main-sequence stage.
Red Giant (Red Supergiant)Red Giant (Red Supergiant) When all the fuel for fusion is used up the giant star
collapses into a small, dense, dying star of low luminosity and high temperature
Red Supergiants have a mass 7 times the Sun’s mass– When a red supergiant starts to collapse, there is a huge
explosion (supernova); everything except the star’s core is blown out into space
– What is left of the core becomes a very dense, invisible pulsar
– This pulsar eventually stops and becomes a neutron star
Red SupergiantsRed Supergiants
Supernova ExplosionSupernova Explosion
White DwarfWhite Dwarf
Cools, turns dull red and shines its leftover heat energy into space
May be hit by another star causing it to flare up temporarily (Nova)
White DwarfWhite Dwarf
Nova Image
Black DwarfBlack Dwarf
Final Stage in a star’s lifeNeutrons collapse into a very small volume
with huge gravitational forcesCold, dark dead starNothing can escapeEx: Cygnus X-1
Black DwarfBlack Dwarf
The SunThe Sun An average medium-
sized star Stable main-sequence
star for approximately 5 billion years
Should continue to shine steadily for another 5 billion years before its hydrogen supply is used up