Stars and Stellar Evolution Unit 6: Astronomy. What are stars? Stars = spheres of very hot gas Stars...
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Transcript of Stars and Stellar Evolution Unit 6: Astronomy. What are stars? Stars = spheres of very hot gas Stars...
Stars and Stellar EvolutionStars and Stellar Evolution
Unit 6: AstronomyUnit 6: AstronomyUnit 6: AstronomyUnit 6: Astronomy
What are stars?What are stars?
Stars = spheres of very hot gasStars = spheres of very hot gasNearest star to Earth is the sunNearest star to Earth is the sunConstellations = group of stars named Constellations = group of stars named
for a mythological charactersfor a mythological characters 8888
Stars = spheres of very hot gasStars = spheres of very hot gasNearest star to Earth is the sunNearest star to Earth is the sunConstellations = group of stars named Constellations = group of stars named
for a mythological charactersfor a mythological characters 8888
Characteristics of StarsCharacteristics of Stars
Star color and Star color and temperaturetemperature Color can give us a Color can give us a
clue to star’s clue to star’s temperaturetemperature
Very hot (above Very hot (above 30,000 K) = blue30,000 K) = blue
Cooler = redCooler = red In-between (5000-In-between (5000-
6000 K) = yellow6000 K) = yellow
Star color and Star color and temperaturetemperature Color can give us a Color can give us a
clue to star’s clue to star’s temperaturetemperature
Very hot (above Very hot (above 30,000 K) = blue30,000 K) = blue
Cooler = redCooler = red In-between (5000-In-between (5000-
6000 K) = yellow6000 K) = yellow
Characteristics of StarsCharacteristics of Stars
Binary stars and stellar Binary stars and stellar massmass Binary star = stars that Binary star = stars that
orbit each other (Pair)orbit each other (Pair) Because of gravityBecause of gravity 50% of all stars50% of all stars
Can calculate mass of Can calculate mass of starstar
Equal mass --> center Equal mass --> center of mass halfway of mass halfway between starsbetween stars
Size of orbits known --> Size of orbits known --> masses can be masses can be calculatedcalculated
Binary stars and stellar Binary stars and stellar massmass Binary star = stars that Binary star = stars that
orbit each other (Pair)orbit each other (Pair) Because of gravityBecause of gravity 50% of all stars50% of all stars
Can calculate mass of Can calculate mass of starstar
Equal mass --> center Equal mass --> center of mass halfway of mass halfway between starsbetween stars
Size of orbits known --> Size of orbits known --> masses can be masses can be calculatedcalculated
Distances to StarsDistances to Stars
Light-year = distance Light-year = distance light travels in a year light travels in a year (9.5 trillion kilometers)(9.5 trillion kilometers)
Parallax = slight shifting Parallax = slight shifting in the apparent position in the apparent position of a nearby star due to of a nearby star due to the orbital motion of the the orbital motion of the EarthEarth Photographs Photographs
(comparisons) --> angle(comparisons) --> angle Nearest = largest angles; Nearest = largest angles;
distant = too small to distant = too small to measuremeasure
Only a few thousand stars Only a few thousand stars are knownare known
Light-year = distance Light-year = distance light travels in a year light travels in a year (9.5 trillion kilometers)(9.5 trillion kilometers)
Parallax = slight shifting Parallax = slight shifting in the apparent position in the apparent position of a nearby star due to of a nearby star due to the orbital motion of the the orbital motion of the EarthEarth Photographs Photographs
(comparisons) --> angle(comparisons) --> angle Nearest = largest angles; Nearest = largest angles;
distant = too small to distant = too small to measuremeasure
Only a few thousand stars Only a few thousand stars are knownare known
How bright is that star?How bright is that star?
Brightness = Brightness = magnitudemagnitude
Apparent magnitude Apparent magnitude = a star’s brightness = a star’s brightness as it appears from as it appears from EarthEarth How big it isHow big it is How hot it isHow hot it is How far away it isHow far away it is Larger number = Larger number =
dimmerdimmer
Brightness = Brightness = magnitudemagnitude
Apparent magnitude Apparent magnitude = a star’s brightness = a star’s brightness as it appears from as it appears from EarthEarth How big it isHow big it is How hot it isHow hot it is How far away it isHow far away it is Larger number = Larger number =
dimmerdimmer
-1.4
How bright is that star?How bright is that star?
Absolute magnitude = how bright a star Absolute magnitude = how bright a star actually isactually is Magnitude of star if I was a distance of Magnitude of star if I was a distance of
32.6 light-years32.6 light-years Ex: Sun = apparent magnitude: -26.7, Ex: Sun = apparent magnitude: -26.7,
absolute magnitude: 5absolute magnitude: 5 More negative = brighter, more positive = More negative = brighter, more positive =
dimmerdimmer
Absolute magnitude = how bright a star Absolute magnitude = how bright a star actually isactually is Magnitude of star if I was a distance of Magnitude of star if I was a distance of
32.6 light-years32.6 light-years Ex: Sun = apparent magnitude: -26.7, Ex: Sun = apparent magnitude: -26.7,
absolute magnitude: 5absolute magnitude: 5 More negative = brighter, more positive = More negative = brighter, more positive =
dimmerdimmer
Hertzsprung-Russell DiagramHertzsprung-Russell Diagram
H-R diagram shows the H-R diagram shows the relationship between the relationship between the absolute magnitude and absolute magnitude and temperature of starstemperature of stars Can also help us infer Can also help us infer
distance, life span massdistance, life span mass Stars are plotted Stars are plotted
according to their according to their temperature and temperature and absolute magnitudeabsolute magnitude
Interpret stellar evolutionInterpret stellar evolution Birth, age, deathBirth, age, death
H-R diagram shows the H-R diagram shows the relationship between the relationship between the absolute magnitude and absolute magnitude and temperature of starstemperature of stars Can also help us infer Can also help us infer
distance, life span massdistance, life span mass Stars are plotted Stars are plotted
according to their according to their temperature and temperature and absolute magnitudeabsolute magnitude
Interpret stellar evolutionInterpret stellar evolution Birth, age, deathBirth, age, death
H-R diagramH-R diagram
Bright stars are near Bright stars are near the top and dimmer the top and dimmer stars are near the stars are near the bottombottom
About 90% are About 90% are main-sequence main-sequence starsstars Hottest = brightestHottest = brightest Coolest = dimmestCoolest = dimmest
Bright stars are near Bright stars are near the top and dimmer the top and dimmer stars are near the stars are near the bottombottom
About 90% are About 90% are main-sequence main-sequence starsstars Hottest = brightestHottest = brightest Coolest = dimmestCoolest = dimmest
H-R diagramH-R diagram
Brightness of main-Brightness of main-sequence stars are sequence stars are related to massrelated to mass Hottest blue stars are 50 Hottest blue stars are 50
times more massive than times more massive than the sunthe sun
Coolest red stars and Coolest red stars and only 1/10 as massiveonly 1/10 as massive
Main-sequence stars Main-sequence stars appear in decreasing appear in decreasing orderorder
Hotter, more massive Hotter, more massive blue stars --> cooler, blue stars --> cooler, less massive red starsless massive red stars
Brightness of main-Brightness of main-sequence stars are sequence stars are related to massrelated to mass Hottest blue stars are 50 Hottest blue stars are 50
times more massive than times more massive than the sunthe sun
Coolest red stars and Coolest red stars and only 1/10 as massiveonly 1/10 as massive
Main-sequence stars Main-sequence stars appear in decreasing appear in decreasing orderorder
Hotter, more massive Hotter, more massive blue stars --> cooler, blue stars --> cooler, less massive red starsless massive red stars
H-R diagramH-R diagram
Red giantsRed giants Above and to right of Above and to right of
main-sequence starsmain-sequence stars Size --> compare Size --> compare
them with stars of them with stars of known size that have known size that have same temperaturesame temperature
Supergiants = Supergiants = biggerbigger Ex: BetelgeuseEx: Betelgeuse
Red giantsRed giants Above and to right of Above and to right of
main-sequence starsmain-sequence stars Size --> compare Size --> compare
them with stars of them with stars of known size that have known size that have same temperaturesame temperature
Supergiants = Supergiants = biggerbigger Ex: BetelgeuseEx: Betelgeuse
Betelgeuse
H-R diagramH-R diagram
White dwarfsWhite dwarfs Lower-central partLower-central part Fainter than main-Fainter than main-
sequence stars of sequence stars of same temperaturesame temperature
White dwarfsWhite dwarfs Lower-central partLower-central part Fainter than main-Fainter than main-
sequence stars of sequence stars of same temperaturesame temperature
Variable StarsVariable Stars
Stars might fluctuate Stars might fluctuate in brightnessin brightness Cepheid variables = Cepheid variables =
brighter and fainter in brighter and fainter in regular patternregular pattern
Nova = sudden Nova = sudden brightening of a starbrightening of a star
Outer layer ejected at Outer layer ejected at high speedhigh speed
Returns to original Returns to original brightnessbrightness
Binary systemsBinary systems
Stars might fluctuate Stars might fluctuate in brightnessin brightness Cepheid variables = Cepheid variables =
brighter and fainter in brighter and fainter in regular patternregular pattern
Nova = sudden Nova = sudden brightening of a starbrightening of a star
Outer layer ejected at Outer layer ejected at high speedhigh speed
Returns to original Returns to original brightnessbrightness
Binary systemsBinary systems
How does the H-R diagram predict stellar evolution?How does the H-R diagram predict stellar evolution?
Illustrate changes Illustrate changes that take place in a that take place in a star in its lifetimestar in its lifetime
Position on H-R Position on H-R diagramdiagram Represents color Represents color
and absolute and absolute magnitude at various magnitude at various stages of evolutionstages of evolution
Illustrate changes Illustrate changes that take place in a that take place in a star in its lifetimestar in its lifetime
Position on H-R Position on H-R diagramdiagram Represents color Represents color
and absolute and absolute magnitude at various magnitude at various stages of evolutionstages of evolution
Stellar EvolutionStellar Evolution
How stars are born, age and dieHow stars are born, age and dieStudy stars of different agesStudy stars of different ages
How stars are born, age and dieHow stars are born, age and dieStudy stars of different agesStudy stars of different ages
Life of a StarLife of a Star
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
Star BirthStar Birth
Born in nebula = Born in nebula = dark, cool, dark, cool, interstellar clouds of interstellar clouds of gas and dustgas and dust Milky Way = 92% Milky Way = 92%
hydrogen, 7% heliumhydrogen, 7% helium Dense --> contracts Dense --> contracts
--> gravity squeezes --> gravity squeezes particles toward particles toward center --> energy center --> energy converted into heat converted into heat energyenergy
Born in nebula = Born in nebula = dark, cool, dark, cool, interstellar clouds of interstellar clouds of gas and dustgas and dust Milky Way = 92% Milky Way = 92%
hydrogen, 7% heliumhydrogen, 7% helium Dense --> contracts Dense --> contracts
--> gravity squeezes --> gravity squeezes particles toward particles toward center --> energy center --> energy converted into heat converted into heat energyenergy
Protostar StageProtostar Stage
Protostar = a developing star not yet hot Protostar = a developing star not yet hot enough to engage in nuclear fusionenough to engage in nuclear fusion Contraction continues --> collapse causes Contraction continues --> collapse causes
the core to heat much more intensely than the core to heat much more intensely than the outer layerthe outer layer
When is a star born?When is a star born? Core of protostar reaches about 10 million Core of protostar reaches about 10 million
K --> nuclear fusion of hydrogen startsK --> nuclear fusion of hydrogen starts
Protostar = a developing star not yet hot Protostar = a developing star not yet hot enough to engage in nuclear fusionenough to engage in nuclear fusion Contraction continues --> collapse causes Contraction continues --> collapse causes
the core to heat much more intensely than the core to heat much more intensely than the outer layerthe outer layer
When is a star born?When is a star born? Core of protostar reaches about 10 million Core of protostar reaches about 10 million
K --> nuclear fusion of hydrogen startsK --> nuclear fusion of hydrogen starts
Balanced ForcesBalanced Forces
Hydrogen fusionHydrogen fusion Gases increase motion --Gases increase motion --
> increase in outward > increase in outward gas pressuregas pressure
Outward pressure from Outward pressure from fusion balances inward fusion balances inward force of gravityforce of gravity
Becomes main-sequence Becomes main-sequence star (stable)star (stable)
Hydrogen fusionHydrogen fusion Gases increase motion --Gases increase motion --
> increase in outward > increase in outward gas pressuregas pressure
Outward pressure from Outward pressure from fusion balances inward fusion balances inward force of gravityforce of gravity
Becomes main-sequence Becomes main-sequence star (stable)star (stable)
Main-sequence stageMain-sequence stage
Balanced between forces of gravity (trying to Balanced between forces of gravity (trying to squeeze into smaller space) and gas squeeze into smaller space) and gas pressure (trying to expand it)pressure (trying to expand it)
Hydrogen fusion for few billion yearsHydrogen fusion for few billion years Hot, massive blue stars deplete fuel in only few Hot, massive blue stars deplete fuel in only few
million yearsmillion years Least massive main sequence remain stable for Least massive main sequence remain stable for
hundreds of billions of yearshundreds of billions of years Yellow star (sun) = 10 billion yearsYellow star (sun) = 10 billion years
90% of life as main-sequence star90% of life as main-sequence star Runs out of hydrogen fuel in core --> diesRuns out of hydrogen fuel in core --> dies
Balanced between forces of gravity (trying to Balanced between forces of gravity (trying to squeeze into smaller space) and gas squeeze into smaller space) and gas pressure (trying to expand it)pressure (trying to expand it)
Hydrogen fusion for few billion yearsHydrogen fusion for few billion years Hot, massive blue stars deplete fuel in only few Hot, massive blue stars deplete fuel in only few
million yearsmillion years Least massive main sequence remain stable for Least massive main sequence remain stable for
hundreds of billions of yearshundreds of billions of years Yellow star (sun) = 10 billion yearsYellow star (sun) = 10 billion years
90% of life as main-sequence star90% of life as main-sequence star Runs out of hydrogen fuel in core --> diesRuns out of hydrogen fuel in core --> dies
Red Giant StageRed Giant Stage
Zone of hydrogen fusion moves outward --> Zone of hydrogen fusion moves outward --> helium corehelium core All hydrogen in core is used up (no fusion in core) All hydrogen in core is used up (no fusion in core)
--> still taking place in outer shell--> still taking place in outer shell Not enough pressure to support itself against force of Not enough pressure to support itself against force of
gravity --> core contractsgravity --> core contracts Core gets hotter --> hydrogen fusion in outer shell Core gets hotter --> hydrogen fusion in outer shell
increases --> expands outer layer --> giant bodyincreases --> expands outer layer --> giant body Surface cools --> redSurface cools --> red Core keeps heating up and converts helium to carbon to Core keeps heating up and converts helium to carbon to
produce energyproduce energy
Zone of hydrogen fusion moves outward --> Zone of hydrogen fusion moves outward --> helium corehelium core All hydrogen in core is used up (no fusion in core) All hydrogen in core is used up (no fusion in core)
--> still taking place in outer shell--> still taking place in outer shell Not enough pressure to support itself against force of Not enough pressure to support itself against force of
gravity --> core contractsgravity --> core contracts Core gets hotter --> hydrogen fusion in outer shell Core gets hotter --> hydrogen fusion in outer shell
increases --> expands outer layer --> giant bodyincreases --> expands outer layer --> giant body Surface cools --> redSurface cools --> red Core keeps heating up and converts helium to carbon to Core keeps heating up and converts helium to carbon to
produce energyproduce energy
Burnout and Death of StarsBurnout and Death of Stars
Low-mass starsLow-mass stars 1/2 mass of sun1/2 mass of sun Consume fuel slowly --> main sequence for Consume fuel slowly --> main sequence for
up to 100 billion yearsup to 100 billion years Consume all their hydrogen --> collapse Consume all their hydrogen --> collapse
into white dwarfsinto white dwarfs Eventually ends up as a black dwarfEventually ends up as a black dwarf
Low-mass starsLow-mass stars 1/2 mass of sun1/2 mass of sun Consume fuel slowly --> main sequence for Consume fuel slowly --> main sequence for
up to 100 billion yearsup to 100 billion years Consume all their hydrogen --> collapse Consume all their hydrogen --> collapse
into white dwarfsinto white dwarfs Eventually ends up as a black dwarfEventually ends up as a black dwarf
Burnout and Death of StarsBurnout and Death of Stars
Medium-mass starsMedium-mass stars Similar to sunSimilar to sun Turn into red giants --> once fuel is gone, Turn into red giants --> once fuel is gone,
collapse as white dwarfs --> eventually collapse as white dwarfs --> eventually black dwarfblack dwarf
Medium-mass starsMedium-mass stars Similar to sunSimilar to sun Turn into red giants --> once fuel is gone, Turn into red giants --> once fuel is gone,
collapse as white dwarfs --> eventually collapse as white dwarfs --> eventually black dwarfblack dwarf
Burnout and Death of StarsBurnout and Death of Stars
Burnout and Death of StarsBurnout and Death of Stars
Massive starsMassive stars Shorter life spansShorter life spans End lives in supernovas End lives in supernovas
= becomes 1 million = becomes 1 million times brighter (rare)times brighter (rare)
Consumes most of its Consumes most of its fuel -> gas pressure does fuel -> gas pressure does not balance gravitational not balance gravitational pull --> collapses --> pull --> collapses --> huge implosion --> shock huge implosion --> shock wave moves out and wave moves out and destroys the star (outer destroys the star (outer shell blasted into space)shell blasted into space)
Massive starsMassive stars Shorter life spansShorter life spans End lives in supernovas End lives in supernovas
= becomes 1 million = becomes 1 million times brighter (rare)times brighter (rare)
Consumes most of its Consumes most of its fuel -> gas pressure does fuel -> gas pressure does not balance gravitational not balance gravitational pull --> collapses --> pull --> collapses --> huge implosion --> shock huge implosion --> shock wave moves out and wave moves out and destroys the star (outer destroys the star (outer shell blasted into space)shell blasted into space)
Formation and Destruction of StarsFormation and Destruction of Stars
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
Stellar RemnantsStellar Remnants
All stars collapse into one of the three: white All stars collapse into one of the three: white dwarf, neutron star, or black holedwarf, neutron star, or black hole
White dwarf = remains of low-mass and medium-White dwarf = remains of low-mass and medium-mass starsmass stars Extremely small with high densities Extremely small with high densities Surface becomes very hotSurface becomes very hot
No energy --> becomes cooler and dimmerNo energy --> becomes cooler and dimmer Last stage of white dwarf = black dwarf (small, cold Last stage of white dwarf = black dwarf (small, cold
body)body) Smallest = most massiveSmallest = most massive
Collapse of larger starsCollapse of larger stars Largest = least massiveLargest = least massive
Collapse of less massive starsCollapse of less massive stars
All stars collapse into one of the three: white All stars collapse into one of the three: white dwarf, neutron star, or black holedwarf, neutron star, or black hole
White dwarf = remains of low-mass and medium-White dwarf = remains of low-mass and medium-mass starsmass stars Extremely small with high densities Extremely small with high densities Surface becomes very hotSurface becomes very hot
No energy --> becomes cooler and dimmerNo energy --> becomes cooler and dimmer Last stage of white dwarf = black dwarf (small, cold Last stage of white dwarf = black dwarf (small, cold
body)body) Smallest = most massiveSmallest = most massive
Collapse of larger starsCollapse of larger stars Largest = least massiveLargest = least massive
Collapse of less massive starsCollapse of less massive stars
Stellar RemnantsStellar Remnants
Neutron star = Neutron star = smaller and more smaller and more massive than white massive than white dwarfsdwarfs Remnants of Remnants of
supernovassupernovas Composed entirely of Composed entirely of
neutronsneutrons
Neutron star = Neutron star = smaller and more smaller and more massive than white massive than white dwarfsdwarfs Remnants of Remnants of
supernovassupernovas Composed entirely of Composed entirely of
neutronsneutrons
Stellar RemnantsStellar Remnants
Supernovae = outer Supernovae = outer layer of star is layer of star is ejected --> collapse ejected --> collapse into hot neutron starinto hot neutron star
Pulsar = emits short Pulsar = emits short bursts of radio bursts of radio energyenergy Remains of Remains of
supernovasupernova
Supernovae = outer Supernovae = outer layer of star is layer of star is ejected --> collapse ejected --> collapse into hot neutron starinto hot neutron star
Pulsar = emits short Pulsar = emits short bursts of radio bursts of radio energyenergy Remains of Remains of
supernovasupernova
Stellar RemnantsStellar Remnants
Black hole = a massive Black hole = a massive star that has collapsed star that has collapsed to such a small volume to such a small volume that its gravity prevents that its gravity prevents the escape of the escape of everythingeverything Cannot be seenCannot be seen Evidence of matter being Evidence of matter being
rapidly swept into an rapidly swept into an areaarea
AnimationAnimation
Black hole = a massive Black hole = a massive star that has collapsed star that has collapsed to such a small volume to such a small volume that its gravity prevents that its gravity prevents the escape of the escape of everythingeverything Cannot be seenCannot be seen Evidence of matter being Evidence of matter being
rapidly swept into an rapidly swept into an areaarea
AnimationAnimation
Where did the elements of the universe come from?Where did the elements of the universe come from? After the universe became cool enough for After the universe became cool enough for
atoms to form, they began to clump together atoms to form, they began to clump together into clouds of gasinto clouds of gas First stars made up of mostly hydrogen with a First stars made up of mostly hydrogen with a
small amount of heliumsmall amount of helium Heavier elements like iron and silicon not yet made Heavier elements like iron and silicon not yet made
inside starsinside stars More and more stars formed, became main-More and more stars formed, became main-
sequence, grew old, and diedsequence, grew old, and died More and more matter was fused into heavier elements More and more matter was fused into heavier elements
and expelled back into interstellar space by supernovas and expelled back into interstellar space by supernovas and dying red giant starsand dying red giant stars
Eventually our sun and its planets formed from this Eventually our sun and its planets formed from this interstellar gas and dustinterstellar gas and dust
After the universe became cool enough for After the universe became cool enough for atoms to form, they began to clump together atoms to form, they began to clump together into clouds of gasinto clouds of gas First stars made up of mostly hydrogen with a First stars made up of mostly hydrogen with a
small amount of heliumsmall amount of helium Heavier elements like iron and silicon not yet made Heavier elements like iron and silicon not yet made
inside starsinside stars More and more stars formed, became main-More and more stars formed, became main-
sequence, grew old, and diedsequence, grew old, and died More and more matter was fused into heavier elements More and more matter was fused into heavier elements
and expelled back into interstellar space by supernovas and expelled back into interstellar space by supernovas and dying red giant starsand dying red giant stars
Eventually our sun and its planets formed from this Eventually our sun and its planets formed from this interstellar gas and dustinterstellar gas and dust
CitationsCitations
TLC Elementary School: The Moon and TLC Elementary School: The Moon and Beyond. Discovery Channel School. Beyond. Discovery Channel School. 2004.unitedstreaming.2004.unitedstreaming.
Science Investigations: Earth Science: Science Investigations: Earth Science: Investigating Astronomy. Discovery Investigating Astronomy. Discovery Channel School. 2004. unitedstreaming. Channel School. 2004. unitedstreaming.
TLC Elementary School: The Moon and TLC Elementary School: The Moon and Beyond. Discovery Channel School. Beyond. Discovery Channel School. 2004.unitedstreaming.2004.unitedstreaming.
Science Investigations: Earth Science: Science Investigations: Earth Science: Investigating Astronomy. Discovery Investigating Astronomy. Discovery Channel School. 2004. unitedstreaming. Channel School. 2004. unitedstreaming.