Stars and Stellar Evolution Unit 6: Astronomy

What are stars? Stars = spheres of very hot gas Stars = spheres of very hot gas Nearest star to Earth is the sun Nearest star to Earth is the sun Constellations = group of stars named for a mythological characters Constellations = group of stars named for a mythological characters Stars = spheres of very hot gas Stars = spheres of very hot gas Nearest star to Earth is the sun Nearest star to Earth is the sun Constellations = group of stars named for a mythological characters Constellations = group of stars named for a mythological characters 88 88

Characteristics of Stars Star color and temperature Star color and temperature Color can give us a clue to star’s temperature Color can give us a clue to star’s temperature Very hot (above 30,000 K) = blue Very hot (above 30,000 K) = blue Cooler = red Cooler = red In-between ( K) = yellow In-between ( K) = yellow Star color and temperature Star color and temperature Color can give us a clue to star’s temperature Color can give us a clue to star’s temperature Very hot (above 30,000 K) = blue Very hot (above 30,000 K) = blue Cooler = red Cooler = red In-between ( K) = yellow In-between ( K) = yellow

Characteristics of Stars Binary stars and stellar mass Binary stars and stellar mass Binary star = stars that orbit each other (Pair) Binary star = stars that orbit each other (Pair) Because of gravity Because of gravity 50% of all stars 50% of all stars Can calculate mass of star Can calculate mass of star Equal mass --> center of mass halfway between stars Equal mass --> center of mass halfway between stars Size of orbits known --> masses can be calculated Size of orbits known --> masses can be calculated Binary stars and stellar mass Binary stars and stellar mass Binary star = stars that orbit each other (Pair) Binary star = stars that orbit each other (Pair) Because of gravity Because of gravity 50% of all stars 50% of all stars Can calculate mass of star Can calculate mass of star Equal mass --> center of mass halfway between stars Equal mass --> center of mass halfway between stars Size of orbits known --> masses can be calculated Size of orbits known --> masses can be calculated

Distances to Stars Light-year = distance light travels in a year (9.5 trillion kilometers) Light-year = distance light travels in a year (9.5 trillion kilometers) Parallax = slight shifting in the apparent position of a nearby star due to the orbital motion of the Earth Parallax = slight shifting in the apparent position of a nearby star due to the orbital motion of the Earth Photographs (comparisons) --> angle Photographs (comparisons) --> angle Nearest = largest angles; distant = too small to measure Nearest = largest angles; distant = too small to measure Only a few thousand stars are known Only a few thousand stars are known Light-year = distance light travels in a year (9.5 trillion kilometers) Light-year = distance light travels in a year (9.5 trillion kilometers) Parallax = slight shifting in the apparent position of a nearby star due to the orbital motion of the Earth Parallax = slight shifting in the apparent position of a nearby star due to the orbital motion of the Earth Photographs (comparisons) --> angle Photographs (comparisons) --> angle Nearest = largest angles; distant = too small to measure Nearest = largest angles; distant = too small to measure Only a few thousand stars are known Only a few thousand stars are known

How bright is that star? Brightness = magnitude Brightness = magnitude Apparent magnitude = a star’s brightness as it appears from Earth Apparent magnitude = a star’s brightness as it appears from Earth How big it is How big it is How hot it is How hot it is How far away it is How far away it is Larger number = dimmer Larger number = dimmer Brightness = magnitude Brightness = magnitude Apparent magnitude = a star’s brightness as it appears from Earth Apparent magnitude = a star’s brightness as it appears from Earth How big it is How big it is How hot it is How hot it is How far away it is How far away it is Larger number = dimmer Larger number = dimmer -1.4

How bright is that star? Absolute magnitude = how bright a star actually is Absolute magnitude = how bright a star actually is Magnitude of star if I was a distance of 32.6 light-years Magnitude of star if I was a distance of 32.6 light-years Ex: Sun = apparent magnitude: -26.7, absolute magnitude: 5 Ex: Sun = apparent magnitude: -26.7, absolute magnitude: 5 More negative = brighter, more positive = dimmer More negative = brighter, more positive = dimmer Absolute magnitude = how bright a star actually is Absolute magnitude = how bright a star actually is Magnitude of star if I was a distance of 32.6 light-years Magnitude of star if I was a distance of 32.6 light-years Ex: Sun = apparent magnitude: -26.7, absolute magnitude: 5 Ex: Sun = apparent magnitude: -26.7, absolute magnitude: 5 More negative = brighter, more positive = dimmer More negative = brighter, more positive = dimmer

Hertzsprung-Russell Diagram H-R diagram shows the relationship between the absolute magnitude and temperature of stars H-R diagram shows the relationship between the absolute magnitude and temperature of stars Can also help us infer distance, life span mass Can also help us infer distance, life span mass Stars are plotted according to their temperature and absolute magnitude Stars are plotted according to their temperature and absolute magnitude Interpret stellar evolution Interpret stellar evolution Birth, age, death Birth, age, death H-R diagram shows the relationship between the absolute magnitude and temperature of stars H-R diagram shows the relationship between the absolute magnitude and temperature of stars Can also help us infer distance, life span mass Can also help us infer distance, life span mass Stars are plotted according to their temperature and absolute magnitude Stars are plotted according to their temperature and absolute magnitude Interpret stellar evolution Interpret stellar evolution Birth, age, death Birth, age, death

H-R diagram Bright stars are near the top and dimmer stars are near the bottom Bright stars are near the top and dimmer stars are near the bottom About 90% are main-sequence stars About 90% are main-sequence stars Hottest = brightest Hottest = brightest Coolest = dimmest Coolest = dimmest Bright stars are near the top and dimmer stars are near the bottom Bright stars are near the top and dimmer stars are near the bottom About 90% are main-sequence stars About 90% are main-sequence stars Hottest = brightest Hottest = brightest Coolest = dimmest Coolest = dimmest

H-R diagram Brightness of main- sequence stars are related to mass Brightness of main- sequence stars are related to mass Hottest blue stars are 50 times more massive than the sun Hottest blue stars are 50 times more massive than the sun Coolest red stars and only 1/10 as massive Coolest red stars and only 1/10 as massive Main-sequence stars appear in decreasing order Main-sequence stars appear in decreasing order Hotter, more massive blue stars --> cooler, less massive red stars Hotter, more massive blue stars --> cooler, less massive red stars Brightness of main- sequence stars are related to mass Brightness of main- sequence stars are related to mass Hottest blue stars are 50 times more massive than the sun Hottest blue stars are 50 times more massive than the sun Coolest red stars and only 1/10 as massive Coolest red stars and only 1/10 as massive Main-sequence stars appear in decreasing order Main-sequence stars appear in decreasing order Hotter, more massive blue stars --> cooler, less massive red stars Hotter, more massive blue stars --> cooler, less massive red stars

H-R diagram Red giants Red giants Above and to right of main-sequence stars Above and to right of main-sequence stars Size --> compare them with stars of known size that have same temperature Size --> compare them with stars of known size that have same temperature Supergiants = bigger Supergiants = bigger Ex: Betelgeuse Ex: Betelgeuse Red giants Red giants Above and to right of main-sequence stars Above and to right of main-sequence stars Size --> compare them with stars of known size that have same temperature Size --> compare them with stars of known size that have same temperature Supergiants = bigger Supergiants = bigger Ex: Betelgeuse Ex: Betelgeuse Betelgeuse

H-R diagram White dwarfs White dwarfs Lower-central part Lower-central part Fainter than main- sequence stars of same temperature Fainter than main- sequence stars of same temperature White dwarfs White dwarfs Lower-central part Lower-central part Fainter than main- sequence stars of same temperature Fainter than main- sequence stars of same temperature

Variable Stars Stars might fluctuate in brightness Stars might fluctuate in brightness Cepheid variables = brighter and fainter in regular pattern Cepheid variables = brighter and fainter in regular pattern Nova = sudden brightening of a star Nova = sudden brightening of a star Outer layer ejected at high speed Outer layer ejected at high speed Returns to original brightness Returns to original brightness Binary systems Binary systems Stars might fluctuate in brightness Stars might fluctuate in brightness Cepheid variables = brighter and fainter in regular pattern Cepheid variables = brighter and fainter in regular pattern Nova = sudden brightening of a star Nova = sudden brightening of a star Outer layer ejected at high speed Outer layer ejected at high speed Returns to original brightness Returns to original brightness Binary systems Binary systems

How does the H-R diagram predict stellar evolution? Illustrate changes that take place in a star in its lifetime Illustrate changes that take place in a star in its lifetime Position on H-R diagram Position on H-R diagram Represents color and absolute magnitude at various stages of evolution Represents color and absolute magnitude at various stages of evolution Illustrate changes that take place in a star in its lifetime Illustrate changes that take place in a star in its lifetime Position on H-R diagram Position on H-R diagram Represents color and absolute magnitude at various stages of evolution Represents color and absolute magnitude at various stages of evolution

Stellar Evolution How stars are born, age and die How stars are born, age and die Study stars of different ages Study stars of different ages How stars are born, age and die How stars are born, age and die Study stars of different ages Study stars of different ages

Life of a Star

Star Birth Born in nebula = dark, cool, interstellar clouds of gas and dust Born in nebula = dark, cool, interstellar clouds of gas and dust Milky Way = 92% hydrogen, 7% helium Milky Way = 92% hydrogen, 7% helium Dense --> contracts - -> gravity squeezes particles toward center --> energy converted into heat energy Dense --> contracts - -> gravity squeezes particles toward center --> energy converted into heat energy Born in nebula = dark, cool, interstellar clouds of gas and dust Born in nebula = dark, cool, interstellar clouds of gas and dust Milky Way = 92% hydrogen, 7% helium Milky Way = 92% hydrogen, 7% helium Dense --> contracts - -> gravity squeezes particles toward center --> energy converted into heat energy Dense --> contracts - -> gravity squeezes particles toward center --> energy converted into heat energy

Protostar Stage Protostar = a developing star not yet hot enough to engage in nuclear fusion Protostar = a developing star not yet hot enough to engage in nuclear fusion Contraction continues --> collapse causes the core to heat much more intensely than the outer layer Contraction continues --> collapse causes the core to heat much more intensely than the outer layer When is a star born? When is a star born? Core of protostar reaches about 10 million K --> nuclear fusion of hydrogen starts Core of protostar reaches about 10 million K --> nuclear fusion of hydrogen starts Protostar = a developing star not yet hot enough to engage in nuclear fusion Protostar = a developing star not yet hot enough to engage in nuclear fusion Contraction continues --> collapse causes the core to heat much more intensely than the outer layer Contraction continues --> collapse causes the core to heat much more intensely than the outer layer When is a star born? When is a star born? Core of protostar reaches about 10 million K --> nuclear fusion of hydrogen starts Core of protostar reaches about 10 million K --> nuclear fusion of hydrogen starts

Balanced Forces Hydrogen fusion Hydrogen fusion Gases increase motion -- > increase in outward gas pressure Gases increase motion -- > increase in outward gas pressure Outward pressure from fusion balances inward force of gravity Outward pressure from fusion balances inward force of gravity Becomes main-sequence star (stable) Becomes main-sequence star (stable) Hydrogen fusion Hydrogen fusion Gases increase motion -- > increase in outward gas pressure Gases increase motion -- > increase in outward gas pressure Outward pressure from fusion balances inward force of gravity Outward pressure from fusion balances inward force of gravity Becomes main-sequence star (stable) Becomes main-sequence star (stable)

Main-sequence stage Balanced between forces of gravity (trying to squeeze into smaller space) and gas pressure (trying to expand it) Balanced between forces of gravity (trying to squeeze into smaller space) and gas pressure (trying to expand it) Hydrogen fusion for few billion years Hydrogen fusion for few billion years Hot, massive blue stars deplete fuel in only few million years Hot, massive blue stars deplete fuel in only few million years Least massive main sequence remain stable for hundreds of billions of years Least massive main sequence remain stable for hundreds of billions of years Yellow star (sun) = 10 billion years Yellow star (sun) = 10 billion years 90% of life as main-sequence star 90% of life as main-sequence star Runs out of hydrogen fuel in core --> dies Runs out of hydrogen fuel in core --> dies Balanced between forces of gravity (trying to squeeze into smaller space) and gas pressure (trying to expand it) Balanced between forces of gravity (trying to squeeze into smaller space) and gas pressure (trying to expand it) Hydrogen fusion for few billion years Hydrogen fusion for few billion years Hot, massive blue stars deplete fuel in only few million years Hot, massive blue stars deplete fuel in only few million years Least massive main sequence remain stable for hundreds of billions of years Least massive main sequence remain stable for hundreds of billions of years Yellow star (sun) = 10 billion years Yellow star (sun) = 10 billion years 90% of life as main-sequence star 90% of life as main-sequence star Runs out of hydrogen fuel in core --> dies Runs out of hydrogen fuel in core --> dies

Red Giant Stage Zone of hydrogen fusion moves outward --> helium core Zone of hydrogen fusion moves outward --> helium core All hydrogen in core is used up (no fusion in core) --> still taking place in outer shell All hydrogen in core is used up (no fusion in core) --> still taking place in outer shell Not enough pressure to support itself against force of gravity --> core contracts Not enough pressure to support itself against force of gravity --> core contracts Core gets hotter --> hydrogen fusion in outer shell increases --> expands outer layer --> giant body Core gets hotter --> hydrogen fusion in outer shell increases --> expands outer layer --> giant body Surface cools --> red Surface cools --> red Core keeps heating up and converts helium to carbon to produce energy Core keeps heating up and converts helium to carbon to produce energy Zone of hydrogen fusion moves outward --> helium core Zone of hydrogen fusion moves outward --> helium core All hydrogen in core is used up (no fusion in core) --> still taking place in outer shell All hydrogen in core is used up (no fusion in core) --> still taking place in outer shell Not enough pressure to support itself against force of gravity --> core contracts Not enough pressure to support itself against force of gravity --> core contracts Core gets hotter --> hydrogen fusion in outer shell increases --> expands outer layer --> giant body Core gets hotter --> hydrogen fusion in outer shell increases --> expands outer layer --> giant body Surface cools --> red Surface cools --> red Core keeps heating up and converts helium to carbon to produce energy Core keeps heating up and converts helium to carbon to produce energy

Burnout and Death of Stars Low-mass stars Low-mass stars 1/2 mass of sun 1/2 mass of sun Consume fuel slowly --> main sequence for up to 100 billion years Consume fuel slowly --> main sequence for up to 100 billion years Consume all their hydrogen --> collapse into white dwarfs Consume all their hydrogen --> collapse into white dwarfs Eventually ends up as a black dwarf Eventually ends up as a black dwarf Low-mass stars Low-mass stars 1/2 mass of sun 1/2 mass of sun Consume fuel slowly --> main sequence for up to 100 billion years Consume fuel slowly --> main sequence for up to 100 billion years Consume all their hydrogen --> collapse into white dwarfs Consume all their hydrogen --> collapse into white dwarfs Eventually ends up as a black dwarf Eventually ends up as a black dwarf

Burnout and Death of Stars Medium-mass stars Medium-mass stars Similar to sun Similar to sun Turn into red giants --> once fuel is gone, collapse as white dwarfs --> eventually black dwarf Turn into red giants --> once fuel is gone, collapse as white dwarfs --> eventually black dwarf Medium-mass stars Medium-mass stars Similar to sun Similar to sun Turn into red giants --> once fuel is gone, collapse as white dwarfs --> eventually black dwarf Turn into red giants --> once fuel is gone, collapse as white dwarfs --> eventually black dwarf

Burnout and Death of Stars

Massive stars Massive stars Shorter life spans Shorter life spans End lives in supernovas = becomes 1 million times brighter (rare) End lives in supernovas = becomes 1 million times brighter (rare) Consumes most of its fuel -> gas pressure does not balance gravitational pull --> collapses --> huge implosion --> shock wave moves out and destroys the star (outer shell blasted into space) Consumes most of its fuel -> gas pressure does not balance gravitational pull --> collapses --> huge implosion --> shock wave moves out and destroys the star (outer shell blasted into space) Massive stars Massive stars Shorter life spans Shorter life spans End lives in supernovas = becomes 1 million times brighter (rare) End lives in supernovas = becomes 1 million times brighter (rare) Consumes most of its fuel -> gas pressure does not balance gravitational pull --> collapses --> huge implosion --> shock wave moves out and destroys the star (outer shell blasted into space) Consumes most of its fuel -> gas pressure does not balance gravitational pull --> collapses --> huge implosion --> shock wave moves out and destroys the star (outer shell blasted into space)

Formation and Destruction of Stars

Stellar Remnants All stars collapse into one of the three: white dwarf, neutron star, or black hole All stars collapse into one of the three: white dwarf, neutron star, or black hole White dwarf = remains of low-mass and medium-mass stars White dwarf = remains of low-mass and medium-mass stars Extremely small with high densities Extremely small with high densities Surface becomes very hot Surface becomes very hot No energy --> becomes cooler and dimmer No energy --> becomes cooler and dimmer Last stage of white dwarf = black dwarf (small, cold body) Last stage of white dwarf = black dwarf (small, cold body) Smallest = most massive Smallest = most massive Collapse of larger stars Collapse of larger stars Largest = least massive Largest = least massive Collapse of less massive stars Collapse of less massive stars All stars collapse into one of the three: white dwarf, neutron star, or black hole All stars collapse into one of the three: white dwarf, neutron star, or black hole White dwarf = remains of low-mass and medium-mass stars White dwarf = remains of low-mass and medium-mass stars Extremely small with high densities Extremely small with high densities Surface becomes very hot Surface becomes very hot No energy --> becomes cooler and dimmer No energy --> becomes cooler and dimmer Last stage of white dwarf = black dwarf (small, cold body) Last stage of white dwarf = black dwarf (small, cold body) Smallest = most massive Smallest = most massive Collapse of larger stars Collapse of larger stars Largest = least massive Largest = least massive Collapse of less massive stars Collapse of less massive stars

Stellar Remnants Neutron star = smaller and more massive than white dwarfs Neutron star = smaller and more massive than white dwarfs Remnants of supernovas Remnants of supernovas Composed entirely of neutrons Composed entirely of neutrons Neutron star = smaller and more massive than white dwarfs Neutron star = smaller and more massive than white dwarfs Remnants of supernovas Remnants of supernovas Composed entirely of neutrons Composed entirely of neutrons

Stellar Remnants Supernovae = outer layer of star is ejected --> collapse into hot neutron star Supernovae = outer layer of star is ejected --> collapse into hot neutron star Pulsar = emits short bursts of radio energy Pulsar = emits short bursts of radio energy Remains of supernova Remains of supernova Supernovae = outer layer of star is ejected --> collapse into hot neutron star Supernovae = outer layer of star is ejected --> collapse into hot neutron star Pulsar = emits short bursts of radio energy Pulsar = emits short bursts of radio energy Remains of supernova Remains of supernova

Stellar Remnants Black hole = a massive star that has collapsed to such a small volume that its gravity prevents the escape of everything Black hole = a massive star that has collapsed to such a small volume that its gravity prevents the escape of everything Cannot be seen Cannot be seen Evidence of matter being rapidly swept into an area Evidence of matter being rapidly swept into an area Animation Animation Animation Black hole = a massive star that has collapsed to such a small volume that its gravity prevents the escape of everything Black hole = a massive star that has collapsed to such a small volume that its gravity prevents the escape of everything Cannot be seen Cannot be seen Evidence of matter being rapidly swept into an area Evidence of matter being rapidly swept into an area Animation Animation Animation

Where did the elements of the universe come from? After the universe became cool enough for atoms to form, they began to clump together into clouds of gas After the universe became cool enough for atoms to form, they began to clump together into clouds of gas First stars made up of mostly hydrogen with a small amount of helium First stars made up of mostly hydrogen with a small amount of helium Heavier elements like iron and silicon not yet made inside stars Heavier elements like iron and silicon not yet made inside stars More and more stars formed, became main- sequence, grew old, and died More and more stars formed, became main- sequence, grew old, and died More and more matter was fused into heavier elements and expelled back into interstellar space by supernovas and dying red giant stars More and more matter was fused into heavier elements and expelled back into interstellar space by supernovas and dying red giant stars Eventually our sun and its planets formed from this interstellar gas and dust Eventually our sun and its planets formed from this interstellar gas and dust After the universe became cool enough for atoms to form, they began to clump together into clouds of gas After the universe became cool enough for atoms to form, they began to clump together into clouds of gas First stars made up of mostly hydrogen with a small amount of helium First stars made up of mostly hydrogen with a small amount of helium Heavier elements like iron and silicon not yet made inside stars Heavier elements like iron and silicon not yet made inside stars More and more stars formed, became main- sequence, grew old, and died More and more stars formed, became main- sequence, grew old, and died More and more matter was fused into heavier elements and expelled back into interstellar space by supernovas and dying red giant stars More and more matter was fused into heavier elements and expelled back into interstellar space by supernovas and dying red giant stars Eventually our sun and its planets formed from this interstellar gas and dust Eventually our sun and its planets formed from this interstellar gas and dust

Citations TLC Elementary School: The Moon and Beyond. Discovery Channel School unitedstreaming. TLC Elementary School: The Moon and Beyond. Discovery Channel School unitedstreaming. Science Investigations: Earth Science: Investigating Astronomy. Discovery Channel School unitedstreaming. Science Investigations: Earth Science: Investigating Astronomy. Discovery Channel School unitedstreaming. TLC Elementary School: The Moon and Beyond. Discovery Channel School unitedstreaming. TLC Elementary School: The Moon and Beyond. Discovery Channel School unitedstreaming. Science Investigations: Earth Science: Investigating Astronomy. Discovery Channel School unitedstreaming. Science Investigations: Earth Science: Investigating Astronomy. Discovery Channel School unitedstreaming.