chapter 11 the interstellar medium
DESCRIPTION
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 PresentationTRANSCRIPT
Copyright © 2010 Pearson Education, Inc.Copyright © 2010 Pearson Education, Inc.
Chapter 11The Interstellar
Medium
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 Clusters
Copyright © 2010 Pearson Education, Inc.
Question 1
Some regions of the Milky Way’s 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.
Question 1
Some regions of the Milky Way’s 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.
Interstellar 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.
Copyright © 2010 Pearson Education, Inc.
Interstellar Matter
Dust clouds absorb blue light preferentially; spectral lines do not shift.
Copyright © 2010 Pearson Education, Inc.
Question 2
When a star’svisible 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.
Question 2
When a star’svisible 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 Sun’s blue light, leaving
dimmer, redder light.
Copyright © 2010 Pearson Education, Inc.
Question 3
Astronomers use the term nebula to refer to
a) 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.
Question 3
Astronomers use the term nebula to refer to
a) 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.
Star-Forming Regions“Nebula” 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.
Question 4
Interstellar gas is composed primarily of
a) 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.
Question 4
Interstellar gas is composed primarily of
a) 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.
Star-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.
Star-Forming RegionsThis is the central section of the Milky Way Galaxy, showing several nebulae, areas of star formation.
Copyright © 2010 Pearson Education, Inc.
Question 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.
Question 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
Glowing hydrogen gas emits red light
around the Horsehead
nebula.
Copyright © 2010 Pearson Education, Inc.
Star-Forming RegionsEmission nebulae generally glow red – this is the Hα 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.
Star-Forming RegionsHow nebulae work
Copyright © 2010 Pearson Education, Inc.
Star-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.
Star-Forming RegionsEmission nebulae are made of hot, thin gas, which exhibits distinct emission lines.
Copyright © 2010 Pearson Education, Inc.
Tarantula Nebula
Copyright © 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.
Dark Dust CloudsThis cloud is very dark, and can be seen only because of the background stars.
Copyright © 2010 Pearson Education, Inc.
Dark Dust CloudsThe Horsehead Nebula is a particularly distinctive dark dust cloud.
Copyright © 2010 Pearson Education, Inc.
Dark Dust CloudsInterstellar gas emits low-energy radiation, due to a transition in the hydrogen atom.
Copyright © 2010 Pearson Education, Inc.
Question 6
21-centimeter radiation is important because
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.
Question 6
21-centimeter radiation is important because
Cool 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.
Dark 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.
Dark 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.
Question 7
Complex molecules in space are found
a) 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.
Question 7
Complex molecules in space are found
a) 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.
Star 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.
When 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 Sun
1057
Copyright © 2010 Pearson Education, Inc.
The Formation of Stars Like the Sun
Stars go through a number of stages in the process of forming from an interstellar cloud.
Copyright © 2010 Pearson Education, Inc.
Question 8
How 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.
Question 8
How 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.
The Formation of Stars Like the Sun
Stage 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.
The Formation of Stars Like the Sun
Stage 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.
The Formation of Stars Like the Sun
The Orion Nebula is thought to contain interstellar clouds in the process of condensing, as well as protostars.
Orion Nebula Mosaic
Copyright © 2010 Pearson Education, Inc.
The Formation of Stars Like the Sun
Stage 4:The core of the cloud is now a protostar, and makes its first appearance on the H–R diagram.
Copyright © 2010 Pearson Education, Inc.
The Formation of Stars Like the Sun
These jets are being emitted as material condenses onto a protostar.
Copyright © 2010 Pearson Education, Inc.
The Formation of Stars Like the Sun
These protostars are in Orion.
Copyright © 2010 Pearson Education, Inc.
The Formation of Stars Like the Sun
Planetary formation has begun, but the protostar is still not in equilibrium – all heating comes from the gravitational collapse.
Copyright © 2010 Pearson Education, Inc.
The Formation of Stars Like the Sun
The last stages can be followed on the H–R diagram:The protostar’s luminosity decreases even as its temperature rises because it is becoming more compact.
Copyright © 2010 Pearson Education, Inc.
The Formation of Stars Like the Sun
At 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.
Stars of Other MassesThis H–R 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.
Stars 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.
Star 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.
Star ClustersThis is a young star cluster called the Pleiades. The H–R diagram of its stars is on the right. This is an example of an open cluster.
Copyright © 2010 Pearson Education, Inc.
Star 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.
Cluster Location
Copyright © 2010 Pearson Education, Inc.
Question 9
a) 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.
Question 9
Very young stars in small clusters of 10-100 members are known as
NGC 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.
Star ClustersThese images are believed to show a star cluster in the process of formation within the Orion Nebula.
Copyright © 2010 Pearson Education, Inc.
Question 10
All stars in a stellar cluster have roughly the same
a) temperature.b) color.c) distance.d) mass.e) luminosity.
Copyright © 2010 Pearson Education, Inc.
Question 10
All stars in a stellar cluster have roughly the same
a) 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.
Star 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 Nebula
Copyright © 2010 Pearson Education, Inc.
Question 11
Stars are often born within groups known as
a) clans.b) spiral waves.c) aggregates.d) clusters.e) swarms.
Copyright © 2010 Pearson Education, Inc.
Question 11
The 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 as
a) clans.b) spiral waves.c) aggregates.d) clusters.e) swarms.
Copyright © 2010 Pearson Education, Inc.
Question 12
Globular clusters are typically observed
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.
Question 12
Globular clusters are typically observed
Globular 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.