Astronomy A BEGINNER’S GUIDE TO THE UNIVERSE EIGHTH EDITION CHAPTER 11 The Interstellar Medium Clickers © 2017 Pearson Education, Inc Question Some regions of the Milky Way’s disk appear dark because a) b) c) there are no stars there stars in that direction are obscured by interstellar gas stars in that direction are obscured by interstellar dust d) © 2017 Pearson Education, Inc numerous black holes capture all the starlight behind them Question Some regions of the Milky Way’s disk appear dark because a) b) c) d) there are no stars there stars in that direction are obscured by interstellar gas stars in that direction are obscured by interstellar dust numerous black holes capture all the starlight behind them Explanation: Dust grains are about the same size as visible light, and they can scatter or block the shorter wavelengths © 2017 Pearson Education, Inc Question When a star’s visible light passes through interstellar dust, the light we see a) b) c) d) e) © 2017 Pearson Education, Inc is dimmed and reddened appears to twinkle is Doppler shifted turns bluish in color ionizes the dust and creates emission lines Question When a star’s visible light passes through interstellar dust, the light we see a) b) c) d) e) is dimmed and reddened appears to twinkle is Doppler shifted turns bluish in color ionizes the dust and creates emission lines Explanation: The same process results in wonderful sunsets, as dust in the air scatters the Sun’s blue light, leaving dimmer, redder light © 2017 Pearson Education, Inc Question Astronomers use the term nebula to refer to a) b) c) d) e) © 2017 Pearson Education, Inc outer envelopes of dying stars that drift gently into space remnants of stars that die by supernova clouds of gas and dust in interstellar space distant galaxies seen beyond our Milky Way All of the above are correct Question Astronomers use the term nebula to refer to a) b) c) d) e) outer envelopes of dying stars that drift gently into space remnants of stars that die by supernova clouds of gas and dust in interstellar space distant galaxies seen beyond our Milky Way All of the above are correct Explanation: Nebula refers to any fuzzy patch—bright or dark—in the sky © 2017 Pearson Education, Inc Question Interstellar gas is composed primarily of a) b) c) d) e) © 2017 Pearson Education, Inc 90% hydrogen, 9% helium, and 1% heavier elements molecules including water and CO2 50% hydrogen and 50% helium hydrogen, oxygen, and nitrogen 99% hydrogen and 1% heavier elements Question Interstellar gas is composed primarily of a) b) c) d) e) 90% hydrogen, 9% helium, and 1% heavier elements molecules including water and CO2 50% hydrogen and 50% helium hydrogen, oxygen, and nitrogen 99% hydrogen and 1% heavier elements Explanation: The composition of interstellar gas mirrors that of the Sun, stars, and the jovian planets © 2017 Pearson Education, Inc Question The reddish color of emission nebulae indicates that a) b) c) d) e) © 2017 Pearson Education, Inc gas and dust are moving away from Earth hydrogen gas is present dying stars have recently exploded cool red stars are hidden inside dust is present Question Very young stars in small clusters of 10–100 members are known as a) b) c) d) e) OB associations molecular cloud complexes aggregates globular clusters hives Explanation: NGC 3603 is a newborn cluster of hot young blue type O and B stars—a perfect OB association © 2017 Pearson Education, Inc Question 10 All stars in a stellar cluster have roughly the same a) b) c) d) e) © 2017 Pearson Education, Inc temperature color distance mass luminosity Question 10 All stars in a stellar cluster have roughly the same a) b) c) d) e) temperature color distance mass luminosity Explanation: Stars in the Pleiades cluster vary in temperature, color, mass, and luminosity, but all lie about 440 light-years away © 2017 Pearson Education, Inc Question 11 Globular clusters are typically observed a) b) c) d) in the plane of our Galaxy above or below the plane of our Galaxy near our Sun in the hearts of other galaxies © 2017 Pearson Education, Inc Question 11 Globular clusters are typically observed a) b) c) d) in the plane of our Galaxy above or below the plane of our Galaxy near our Sun in the hearts of other galaxies Explanation: Globular clusters orbit the center of the Milky Way and are usually seen above or below the galactic plane far from our Sun © 2017 Pearson Education, Inc Question 12 Stars in clusters and associations have about the same a) b) c) d) e) © 2017 Pearson Education, Inc age temperature mass color luminosity Question 12 Stars in clusters and associations have about the same a) b) c) d) e) age temperature mass color luminosity Explanation: Most of the stars in a cluster form about the same time Stars in the Omega Centauri globular cluster are estimated to be about 14 billion years old © 2017 Pearson Education, Inc Question 13 Objects more massive than our Sun form into stars a) b) c) d) © 2017 Pearson Education, Inc much slower, over billions of years in about the same time much faster, over tens of thousands of years not at all—they are unstable Question 13 Objects more massive than our Sun form into stars a) b) c) much slower, over billions of years in about the same time much faster, over tens of thousands of years d) not at all—they are unstable Explanation: More mass → faster collapse More mass → faster start of fusion reactions More mass → a hotter, more luminous main-sequence star © 2017 Pearson Education, Inc Question 14 How single stars form within huge clouds of interstellar gas and dust? a) Clouds fragment into smaller objects, forming many stars at one time b) c) © 2017 Pearson Education, Inc One star forms; other matter goes into planets, moons, asteroids, and comets Clouds rotate and throw off mass until only enough is left to form one star Question 14 How single stars form within huge clouds of interstellar gas and dust? a) b) c) Clouds fragment into smaller objects, forming many stars at one time One star forms; other matter goes into planets, moons, asteroids, and comets Clouds rotate and throw off mass until only enough is left to form one star Explanation: The theory of star formation predicts stars in a cluster would form about the same time © 2017 Pearson Education, Inc Question 15 What is a T-Tauri star? a) b) c) d) e) © 2017 Pearson Education, Inc A collapsing cloud of gas about to become a protostar A dying star A cool main-sequence star A star releasing a planetary nebula A protostar about to become a star Question 15 What is a T-Tauri star? a) b) c) d) e) A collapsing cloud of gas about to become a protostar A dying star A cool main-sequence star A star releasing a planetary nebula A protostar about to become a star Explanation: T-Tauri stars often show jets of gas emitted in two directions— bipolar flow—suggesting they are not yet stable © 2017 Pearson Education, Inc Question 16 A key feature of globular clusters is that they have a) b) c) d) e) © 2017 Pearson Education, Inc very few cool stars the oldest stars in our Galaxy lots of massive main-sequence stars stars with very different ages high concentrations of metals Question 16 A key feature of globular clusters is that they have a) b) c) d) e) very few cool stars the oldest stars in our Galaxy lots of massive main-sequence stars stars with very different ages high concentrations of metals Explanation: The H–R diagram of a globular cluster has a low “turnoff point,” indicating its extreme age © 2017 Pearson Education, Inc ... 15 What is a T-Tauri star? a) b) c) d) e) A collapsing cloud of gas about to become a protostar A dying star A cool main-sequence star A star releasing a planetary nebula A protostar about to become... 2017 Pearson Education, Inc A collapsing cloud of gas about to become a protostar A dying star A cool main-sequence star A star releasing a planetary nebula A protostar about to become a star Question... plane of our Galaxy above or below the plane of our Galaxy near our Sun in the hearts of other galaxies Explanation: Globular clusters orbit the center of the Milky Way and are usually seen above