Chapter 30 Section 2 Chapter 30 Section 2 HandoutHandout

Stellar EvolutionStellar Evolution

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Why are astronomers not able to observe Why are astronomers not able to observe the entire life of any star?the entire life of any star? Because a star typically exists for billions of Because a star typically exists for billions of

years.years.

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What is luminosity?What is luminosity? The total amount of energy a star gives off The total amount of energy a star gives off

each second.each second.

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What is the Hertzsprung-Russell diagram?What is the Hertzsprung-Russell diagram? The graph that illustrates the pattern revealed The graph that illustrates the pattern revealed

when the surface temperatures of stars are when the surface temperatures of stars are plotted against their luminosity.plotted against their luminosity.

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What is plotted on the What is plotted on the horizontal axis and horizontal axis and the vertical axis of the the vertical axis of the Hertzsprung-Russell Hertzsprung-Russell (H-R) diagram?(H-R) diagram? Horizontal axis: The Horizontal axis: The

temperature of a star’s temperature of a star’s surface.surface.

Vertical axis: The Vertical axis: The luminosity of a star.luminosity of a star.

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What is the main sequence?What is the main sequence? The band that runs diagonally through the The band that runs diagonally through the

Hertzsprung-Russell diagram and extends Hertzsprung-Russell diagram and extends from cool, dim, red stars at the lower right to from cool, dim, red stars at the lower right to hot, bright, blue stars at the upper left.hot, bright, blue stars at the upper left.

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What is a nebula?What is a nebula? A: A cloud of gas and dust where a star A: A cloud of gas and dust where a star

begins.begins.

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What is Newton’s law What is Newton’s law of universal of universal gravitation?gravitation? D: All objects in the D: All objects in the

universe attract each universe attract each other through other through gravitational force.gravitational force.

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Gravitational force increases as the mass Gravitational force increases as the mass of an object:of an object: C: Increases or as the distance between two C: Increases or as the distance between two

objects decreases.objects decreases.

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What is a protostar?What is a protostar? A shrinking, spinning region that begins to A shrinking, spinning region that begins to

flatten into a disk with a central concentration flatten into a disk with a central concentration of matter.of matter.

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What happens as more matter is pulled What happens as more matter is pulled into a protostar?into a protostar? Gravitational energy is converted into heat Gravitational energy is converted into heat

energy, and the temperature of the protostar energy, and the temperature of the protostar increases.increases.

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What is important about the onset of What is important about the onset of fusion?fusion? It marks the birth of a star.It marks the birth of a star.

Life Cycles of StarsLife Cycles of Stars

Stars are born (nebular theory)Stars are born (nebular theory)

They all start like our sun converting They all start like our sun converting hydrogen into helium by high temperature hydrogen into helium by high temperature and nuclear fusionand nuclear fusion

Life Cycle of Stars by MASSLife Cycle of Stars by MASS

Nebula-gas and dust

Protostars

Star like our sun

Massive star

Red giant

Red supergiant

Planetary nebula

White dwarf then black dwarf?

supernovaNeutron star and/or black hole

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What happens as gravity increases the What happens as gravity increases the pressure on the matter within a star?pressure on the matter within a star? The rate of fusion increases.The rate of fusion increases.

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What does the equilibrium between the What does the equilibrium between the outward pressures of radiation and the outward pressures of radiation and the force of gravity do?force of gravity do? It makes the star stable in size.It makes the star stable in size.

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How long does a main sequence star How long does a main sequence star maintain a stable size?maintain a stable size? As long as it has an ample supply of hydrogen As long as it has an ample supply of hydrogen

to fuse into helium.to fuse into helium.

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What is the second and longest stage in What is the second and longest stage in the life of a star?the life of a star? C: The main-sequence stage.C: The main-sequence stage.

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A star that has the same mass as the A star that has the same mass as the sun’s mass:sun’s mass: B: Stays on the main sequence for about 10 B: Stays on the main sequence for about 10

billion years.billion years.

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When does a star enter its third stage?When does a star enter its third stage? When almost all of the hydrogen atoms in its When almost all of the hydrogen atoms in its

core have fused into helium atoms.core have fused into helium atoms.

Nucleosynthesis and Fusion Nucleosynthesis and Fusion Reactions Reactions

The main process responsible for the energy produced in most main sequence stars is the proton-proton (pp) chain.

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What does increased temperature from What does increased temperature from contraction in the core cause the helium contraction in the core cause the helium core to do?core to do? As the helium core becomes hotter, it As the helium core becomes hotter, it

transfers energy into a thin shell of hydrogen transfers energy into a thin shell of hydrogen surrounding the core. As it gets hotter the surrounding the core. As it gets hotter the outer hydrogen shell will emit more energy outer hydrogen shell will emit more energy causing the star to expand to be a giant.causing the star to expand to be a giant.

Red Giant StarsRed Giant Stars

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Describe the stars Describe the stars known as giants and known as giants and their place on the H-R their place on the H-R diagram.diagram. They are large, red They are large, red

stars whose hot core stars whose hot core has used most of its has used most of its hydrogen.hydrogen.

They are above the They are above the main sequence.main sequence.

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What are supergiants?What are supergiants? Main-sequence stars that are more massive Main-sequence stars that are more massive

than the sun and become larger than regular than the sun and become larger than regular giant stars.giant stars.

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What is a planetary nebula?What is a planetary nebula? A: A cloud of gas that forms around a sun like A: A cloud of gas that forms around a sun like

star that is dying.star that is dying.

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What is a white dwarf?What is a white dwarf? C: A hot, extremely dense core of matter C: A hot, extremely dense core of matter

leftover from an old star.leftover from an old star.

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What is a black dwarf?What is a black dwarf? A: A white dwarf that no longer gives off light.A: A white dwarf that no longer gives off light.

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An explosion on a white dwarf caused by a An explosion on a white dwarf caused by a pressure build-up is a:pressure build-up is a: D: NovaD: Nova

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What effect may a nova have on a star?What effect may a nova have on a star? A: It may cause it to become many thousands A: It may cause it to become many thousands

of times brighter.of times brighter.

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Describe a supernova and how it differs Describe a supernova and how it differs from a nova.from a nova. A supernova is a star that has such a A supernova is a star that has such a

tremendous explosion that it blows itself tremendous explosion that it blows itself apart.apart.

Unlike a nova, a white dwarf can sometimes Unlike a nova, a white dwarf can sometimes accumulate so much mass on its surface that accumulate so much mass on its surface that gravity overwhelms the outward pressure.gravity overwhelms the outward pressure.

The star collapses and is so dense that the The star collapses and is so dense that the outer layers rebound and explode.outer layers rebound and explode.

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Stars that have masses of more than 8 Stars that have masses of more than 8 times the sun’s mass produce supernovas:times the sun’s mass produce supernovas: C: Without needing a secondary star to fuel C: Without needing a secondary star to fuel

them.them.

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What is a neutron star?What is a neutron star? A star that has collapsed under gravity to the A star that has collapsed under gravity to the

point that the electrons and protons have point that the electrons and protons have smashed together to form neutrons.smashed together to form neutrons.

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Describe how a black hole forms.Describe how a black hole forms. the remaining core of a star has more than 3 the remaining core of a star has more than 3

times the mass of the suntimes the mass of the sun the star may contract further under its greater the star may contract further under its greater

gravity.gravity. The force of the contraction crushes the The force of the contraction crushes the

dense core of the star and leaves a black dense core of the star and leaves a black hole.hole.

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Why is locating black holes difficult?Why is locating black holes difficult? Because black holes do not give off light.Because black holes do not give off light. light cannot escape its gravity.light cannot escape its gravity.

Picture of a black hole

The End?The End?