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Copyright © 2010 Pearson Education, Inc. Copyright © 2010 Pearson Education, Inc. Chapter 11 The Interstellar Medium

Chapter 11 The Interstellar Medium

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Chapter 11 The Interstellar Medium. Units of Chapter 11. Interstellar Matter Star-Forming Regions Dark Dust Clouds The Formation of Stars Like the Sun Stars of Other Masses Star Clusters. Question 1. a) there are no stars there. - PowerPoint PPT Presentation

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Chapter 11The Interstellar MediumCopyright 2010 Pearson Education, Inc.

Copyright 2010 Pearson Education, Inc.

Copyright 2010 Pearson Education, Inc.Units of Chapter 11Interstellar MatterStar-Forming RegionsDark Dust CloudsThe Formation of Stars Like the SunStars of Other MassesStar ClustersCopyright 2010 Pearson Education, Inc.3Question 1Some regions of the Milky Ways disk appear dark because a) there are no stars there.b) stars in that direction are obscured by interstellar gas.c) stars in that direction are obscured by interstellar dust.d) numerous black holes capture all the starlight behind them.

Copyright 2010 Pearson Education, Inc.4Answer: cQuestion 1Some regions of the Milky Ways disk appear dark because a) there are no stars there.b) stars in that direction are obscured by interstellar gas.c) stars in that direction are obscured by interstellar dust.d) numerous black holes capture all the starlight behind them.Dust grains are about the same size as visible light, and they can scatter or block the shorter wavelengths.

Copyright 2010 Pearson Education, Inc.5Interstellar MatterThe interstellar medium consists of gas and dust.Gas is atoms and small molecules, mostly hydrogen and helium.Dust is more like soot or smoke; larger clumps of particles.Dust absorbs light, and reddens light that gets through. This image shows distinct reddening of stars near the edge of the dust cloud.

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Interstellar MatterDust clouds absorb blue light preferentially; spectral lines do not shift.Copyright 2010 Pearson Education, Inc.7Question 2When a starsvisible light passes through interstellar dust, the light we see a) is dimmed and reddened.b) appears to twinkle. c) is Doppler shifted. d) turns bluish in color.e) ionizes the dust and creates emission lines.

Copyright 2010 Pearson Education, Inc.8Answer: aQuestion 2When a starsvisible light passes through interstellar dust, the light we see a) is dimmed and reddened.b) appears to twinkle. c) is Doppler shifted. d) turns bluish in color.e) ionizes the dust and creates emission lines.The same process results in wonderful sunsets, as dust in the air scatters the Suns blue light, leaving dimmer, redder light.

Copyright 2010 Pearson Education, Inc.9Question 3Astronomers use the term nebula to refer toa) outer envelopes of dying stars that drift gently into space.b) remnants of stars that die by supernova.c) clouds of gas and dust in interstellar space.d) distant galaxies seen beyond our Milky Way.e) All of the above are correct.

Copyright 2010 Pearson Education, Inc.10Answer: eQuestion 3Astronomers use the term nebula to refer toa) outer envelopes of dying stars that drift gently into space.b) remnants of stars that die by supernova.c) clouds of gas and dust in interstellar space.d) distant galaxies seen beyond our Milky Way.e) All of the above are correct.Nebula refers to any fuzzy patch bright or dark in the sky.

Copyright 2010 Pearson Education, Inc.11Star-Forming RegionsNebula is a general term used for fuzzy objects in the sky.Dark nebula: dust cloudEmission nebula: glows, due to hot stars

Copyright 2010 Pearson Education, Inc.12Question 4Interstellar gas is composed primarily ofa) 90% hydrogen, 9% helium, and 1% heavier elements.b) molecules including water and CO2.c) 50% hydrogen, 50% helium.d) hydrogen, oxygen, and nitrogen.e) 99% hydrogen, and 1% heavier elements.

Copyright 2010 Pearson Education, Inc.13Answer: aQuestion 4Interstellar gas is composed primarily ofa) 90% hydrogen, 9% helium, and 1% heavier elements.b) molecules including water and CO2.c) 50% hydrogen, 50% helium.d) hydrogen, oxygen, and nitrogen.e) 99% hydrogen, and 1% heavier elements.The composition of interstellar gas mirrors that of the Sun, stars, and the jovian planets.

Copyright 2010 Pearson Education, Inc.14Star-Forming RegionsThese nebulae are very large and have very low density; their size means that their masses are large despite the low density.

Copyright 2010 Pearson Education, Inc.15Star-Forming RegionsThis is the central section of the Milky Way Galaxy, showing several nebulae, areas of star formation.

Copyright 2010 Pearson Education, Inc.16Question 5a) gas and dust is moving away from Earth.b) hydrogen gas is present.c) dying stars have recently exploded.d) cool red stars are hidden inside.e) dust is present.The reddish color of emission nebulae indicates that

Copyright 2010 Pearson Education, Inc.17Answer: bQuestion 5a) gas and dust is moving away from Earth.b) hydrogen gas is present.c) dying stars have recently exploded.d) cool red stars are hidden inside.e) dust is present.The reddish color of emission nebulae indicates thatGlowing hydrogen gas emits red light around the Horsehead nebula.

Copyright 2010 Pearson Education, Inc.18Star-Forming RegionsEmission nebulae generally glow red this is the H line of hydrogen.The dust lanes visible in the previous image are part of the nebula, and are not due to intervening clouds.

Copyright 2010 Pearson Education, Inc.19Star-Forming RegionsHow nebulae work

Copyright 2010 Pearson Education, Inc.20Star-Forming RegionsThere is a strong interaction between the nebula and the stars within it; the fuzzy areas near the pillars are due to photoevaporation.

Copyright 2010 Pearson Education, Inc.21Star-Forming RegionsEmission nebulae are made of hot, thin gas, which exhibits distinct emission lines.

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Tarantula NebulaCopyright 2010 Pearson Education, Inc.Dark Dust CloudsAverage temperature of dark dust clouds is a few tens of kelvins.These clouds absorb visible light (left), and emit radio wavelengths (right).

Copyright 2010 Pearson Education, Inc.24Dark Dust CloudsThis cloud is very dark, and can be seen only because of the background stars.

Copyright 2010 Pearson Education, Inc.25Dark Dust CloudsThe Horsehead Nebula is a particularly distinctive dark dust cloud.

Copyright 2010 Pearson Education, Inc.26Dark Dust CloudsInterstellar gas emits low-energy radiation, due to a transition in the hydrogen atom.

Copyright 2010 Pearson Education, Inc.27Question 621-centimeter radiation is important becausea) its radio waves pass unaffected through clouds of interstellar dust.b) it arises from cool helium gas present throughout space.c) it can be detected with optical telescopes.d) it is produced by protostars. e) it reveals the structure of new stars.

Copyright 2010 Pearson Education, Inc.28Answer: aQuestion 621-centimeter radiation is important becauseCool atomic hydrogen gas produces 21-cm radio radiation as its electron flips its direction of spin.a) its radio waves pass unaffected through clouds of interstellar dust.b) it arises from cool helium gas present throughout space.c) it can be detected with optical telescopes.d) it is produced by protostars. e) it reveals the structure of new stars.

Copyright 2010 Pearson Education, Inc.29Dark Dust CloudsThis is a contour map of H2CO near the M20 Nebula. Other molecules that can be useful for mapping out these clouds are carbon dioxide and water.Here, the red and green lines correspond to different rotational transitions. (frequencies)

Copyright 2010 Pearson Education, Inc.30Dark Dust CloudsThese are CO (carbon monoxide) emitting clouds in the outer Milky Way, probably corresponding to regions of star formation.

Copyright 2010 Pearson Education, Inc.31Question 7Complex molecules in space are founda) in the photospheres of red giant stars.b) primarily inside dense dust clouds.c) in the coronas of stars like our Sun.d) scattered evenly throughout interstellar space.e) surrounding energetic young stars.

Copyright 2010 Pearson Education, Inc.32Answer: bQuestion 7Complex molecules in space are founda) in the photospheres of red giant stars.b) primarily inside dense dust clouds.c) in the coronas of stars like our Sun.d) scattered evenly throughout interstellar space.e) surrounding energetic young stars.A radio telescope image of the outer portion of the Milky Way, revealing molecular cloud complexes.

Copyright 2010 Pearson Education, Inc.33Star formation happens when part of a dust cloud begins to contract under its own gravitational force; as it collapses, the center becomes hotter and hotter until nuclear fusion begins in the core.The Formation of Stars Like the Sun

Copyright 2010 Pearson Education, Inc.34When looking at just a few atoms, the gravitational force is nowhere near strong enough to overcome the random thermal motion.

The Formation of Stars Like the Sun1057Copyright 2010 Pearson Education, Inc.35The Formation of Stars Like the SunStars go through a number of stages in the process of forming from an interstellar cloud.

Copyright 2010 Pearson Education, Inc.36Question 8How do single stars form within huge clouds of interstellar gas and dust?a) Clouds fragment into smaller objects, forming many stars at one time.

b) One star forms; other matter goes into planets, moons, asteroids, & comets.

c) Clouds rotate & throw off mass until only enough is left to form one star.

Copyright 2010 Pearson Education, Inc.37Answer: aQuestion 8How do single stars form within huge clouds of interstellar gas and dust?a) Clouds fragment into smaller objects, forming many stars at one time.

b) One star forms; other matter goes into planets, moons, asteroids, & comets.

c) Clouds rotate & throw off mass until only enough is left to form one star.The theory of star formation predicts stars in a cluster would form about the same time.

Copyright 2010 Pearson Education, Inc.38The Formation of Stars Like the SunStage 1:Interstellar cloud starts to contract, probably triggered by shock or pressure wave from nearby star. As it contracts, the cloud fragments into smaller pieces.

Copyright 2010 Pearson Education, Inc.39The Formation of Stars Like the SunStage 2:Individual cloud fragments begin to collapse. Once the density is high enough, there is no further fragmentation.Stage 3: The interior of the fragment has begun heating, and is about 10,000 K.Copyright 2010 Pearson Education, Inc.40

The Formation of Stars Like the SunThe Orion Nebula is thought to contain interstellar clouds in the process of condensing, as well as protostars.Orion Nebula MosaicCopyright 2010 Pearson Education, Inc.41The Formation of Stars Like the SunStage 4:The core of the cloud is now a protostar, and makes its first appearance on the HR diagram.

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The Formation of Stars Like the SunThese jets are being emitted as material condenses onto a protostar.Copyright 2010 Pearson Education, Inc.43The Formation of Stars Like the SunThese protostars are in Orion.

Copyright 2010 Pearson Education, Inc.44The Formation of Stars Like the SunPlanetary formation has begun, but the protostar is still not in equilibrium all heating comes from the gravitational collapse.

Copyright 2010 Pearson Education, Inc.45The Formation of Stars Like the SunThe last stages can be followed on the HR diagram:The protostars luminosity decreases even as its temperature rises because it is becoming more compact.

Copyright 2010 Pearson Education, Inc.46The Formation of Stars Like the SunAt stage 6, the core reaches 10 million K, and nuclear fusion begins. The protostar has become a star.The star continues to contract and increase in temperature, until it is in equilibrium. This is stage 7: the star has reached the main sequence and will remain there as long as it has hydrogen to fuse in its core.Copyright 2010 Pearson Education, Inc.47Stars of Other MassesThis HR diagram shows the evolution of stars somewhat more and somewhat less massive than the Sun. The shape of the paths is similar, but they wind up in different places on the main sequence.

Copyright 2010 Pearson Education, Inc.48Stars of Other MassesIf the mass of the original nebular fragment is too small, nuclear fusion will never begin. These failed stars are called brown dwarfs.

Copyright 2010 Pearson Education, Inc.49Star ClustersBecause a single interstellar cloud can produce many stars of the same age and composition, star clusters are an excellent way to study the effect of mass on stellar evolution.

Copyright 2010 Pearson Education, Inc.50Star ClustersThis is a young star cluster called the Pleiades. The HR diagram of its stars is on the right. This is an example of an open cluster.

Copyright 2010 Pearson Education, Inc.51Star ClustersThis is a globular cluster note the absence of massive main-sequence stars, and the heavily populated red giant region.

Copyright 2010 Pearson Education, Inc.52Cluster Location

Copyright 2010 Pearson Education, Inc.Question 9a) OB associations.b) molecular cloud complexes.c) aggregates.d) globular clusters.e) hives.Very young stars in small clusters of 10-100 members are known as

Copyright 2010 Pearson Education, Inc.54Answer: aQuestion 9Very young stars in small clusters of 10-100 members are known asNGC 3603 is a newborn cluster of hot young blue Type O and B stars a perfect OB association. a) OB associations.b) molecular cloud complexes.c) aggregates.d) globular clusters.e) hives.

Copyright 2010 Pearson Education, Inc.55Star ClustersThese images are believed to show a star cluster in the process of formation within the Orion Nebula.

Copyright 2010 Pearson Education, Inc.56Question 10All stars in a stellar cluster have roughly the samea) temperature.b) color.c) distance.d) mass.e) luminosity.

Copyright 2010 Pearson Education, Inc.57Answer: cQuestion 10All stars in a stellar cluster have roughly the samea) temperature.b) color.c) distance.d) mass.e) luminosity.Stars in the Pleiades cluster vary in temperature, color, mass, and luminosity, but all lie about 440 light-years away.

Copyright 2010 Pearson Education, Inc.58Star ClustersThe presence of massive, short-lived O and B stars can profoundly affect their star cluster, as they can blow away dust and gas before it has time to collapse.This is a simulation of such a cluster.

Carina NebulaCopyright 2010 Pearson Education, Inc.59Question 11Stars are often born within groups known asa) clans.b) spiral waves.c) aggregates.d) clusters.e) swarms.

Copyright 2010 Pearson Education, Inc.60Answer: dQuestion 11The Pleiades a nearby open cluster is a group of relatively young stars about 400 light-years from the Sun.Stars are often born within groups known asa) clans.b) spiral waves.c) aggregates.d) clusters.e) swarms.

Copyright 2010 Pearson Education, Inc.61Question 12Globular clusters are typically observeda) in the plane of our Galaxy.b) above or below the plane of our Galaxy.c) near to our Sun.d) in the hearts of other galaxies.

Copyright 2010 Pearson Education, Inc.62Answer: bQuestion 12Globular clusters are typically observedGlobular clusters orbit the center of the Milky Way, and are usually seen above or below the galactic plane far from our Sun.a) in the plane of our Galaxy.b) above or below the plane of our Galaxy.c) near to our Sun.d) in the hearts of other galaxies.

Copyright 2010 Pearson Education, Inc.63Summary of Chapter 11 Interstellar medium is made of gas and dust. Emission nebulae are hot, glowing gas associated with the formation of large stars. Dark dust clouds, especially molecular clouds, are very cold. They may seed the beginnings of star formation. Dark clouds can be studied using the 21-cm emission line of molecular hydrogen. Star formation begins with fragmenting, collapsing cloud of dust and gas.Copyright 2010 Pearson Education, Inc.64Summary of Chapter 11, cont. The cloud fragment collapses due to its own gravity, and its temperature and luminosity increase. When the core is sufficiently hot, fusion begins. Collapsing cloud fragments and protostars have been observed. Mass determines where a star falls on the main sequence. One cloud typically forms many stars, as a star cluster.Copyright 2010 Pearson Education, Inc.65