Test Bank Docx The Formation of Stars and Planets Ch5

Chapter 5: The Formation of Stars and Planets

LEARNING OBJECTIVES

5.1 Molecular Clouds Are the Cradles of Star Formation

5.1a Describe how hydrostatic equilibrium supports a self-gravitating object.

5.1b Describe what constitutes a molecular cloud.

5.1c Describe the process of fragmentation during the collapse of a cloud.

5.1d Describe how a molecular cloud becomes a protostar.

5.2 The Protostar Becomes a Star

5.2a Explain why conversion of gravitational to thermal energy heats a collapsing gas.

5.2b Describe the conditions required for the protostar to become a star.

5.3 Planets Form in a Disk around the Protostar

5.3a Explain conservation of angular momentum.

5.3b Describe how accretion disks transfer angular momentum so that stars and planets can collapse.

5.3c Describe the formation sequence of planetesimals in an accretion disk.

5.4 The Inner and Outer Disk Have Different compositions

5.4a Distinguish between refractory and volatile materials.

5.4b Relate the temperature of an accretion disk to the presence of different types of materials (for example, refractory, volatile, organic, ice) within the disk.

5.4c Distinguish between primary and secondary atmospheres.

5.5 A Case study: the Solar system

5.5a Compare and contrast terrestrial and Jovian planets.

5.5b Describe how planetesimals become planets.

5.5c Show how temperature differences in our accretion disk led to the formation of terrestrial and Jovian planets.

5.6 Planetary systems are Common

5.6a Summarize the five methods that astronomers use to detect extrasolar planets.

5.6b Describe how planetary migration accounts for hot Jupiters being located very close to their host stars.

Working It Out 5.1

Working It Out 5.1a Use the Stefan Boltzmann law to relate temperature, flux, and luminosity of a blackbody.

Working It Out 5.1b Use Wien’s law to relate the temperature and peak wavelength of blackbody emission.

Working It Out 5.2

Working It Out 5.2a Use the Doppler equation to relate radial velocity to shifts in the wavelengths of spectral lines.

Chapter 5: The Formation of Stars and Planets

MULTIPLE CHOICE

1. Examine the following figure. What causes molecular clouds to collapse?

a. conservation of charge c. thermal energy

b. self-gravity d. radiation

2. Three stars are found to have been formed from a molecular cloud. How many high-density fragments must have existed in the cloud before star formation?

a. exactly three c. three or more

b. only one d. none

3. The core of a molecular cloud collapses to half its original size so that different parts of the cloud are, on average, only half as far apart as when the collapse started. How has the pull of gravity between these parts in the cloud changed?

a. no change c. twice as strong

b. half as strong d. four times as strong

4. What would a cloud of gas in hydrostatic equilibrium do?

a. collapse c. fragment

b. expand d. stay the same

5. What is the primary constituent of a molecular cloud?

a. water molecules c. dust

b. hydrogen molecules d. various gases

6. What happens when a molecular-cloud core gets very dense?

a. Nothing. It remains in hydrostatic equilibrium.

b. It collapses uniformly.

c. It collapses from the inside out.

d. It collapses from the outside in.

7. The increasing temperature of the core of a collapsing cloud of gas is due to

a. radiation. c. increased spin rate of the cloud.

b. collisions between gas molecules. d. fragmentation of the core.

8. What happens to the gravitational energy of gas as it falls toward and eventually hits the accretion disk surrounding a protostar?

a. It is converted into thermal energy, heating the disk.

b. It is converted into light energy, giving off a flash of light on impact.

c. It is converted into potential energy as the gas plows through the disk and comes out the other side.

d. It simply dissipates.

9. What object forms if a protostar mass is less than 0.08 solar masses?

a. Jupiter-type planet c. nebula

b. brown dwarf d. low-mass star

10. What must occur for a protostar to become a star?

a. fusion in its core c. formation of an accretion disk

b. hydrostatic equilibrium d. formation of planetesimals

11. According to the Stefan-Boltzmann law, by how much would the flux of a body increase if only its temperature doubled?

a. The flux would not change because it does not depend on temperature.

b. twice the flux

c. four times the flux

d. sixteen times the flux

12. What happens to the peak of a blackbody curve seen in an intensity versus wavelength plot if the temperature of a blackbody is increased?

a. The peak would not change because it does not depend on temperature.

b. The peak moves up in intensity only.

c. The peak moves to a shorter wavelength only.

d. The peak moves both up in intensity and over to a shorter wavelength.

13. A blackbody radiates at 6,000 kelvin (K). The peak of this blackbody curve in an intensity versus wavelength plot will occur at what wavelength?

a. 483 nanometers (nm) c. 0.00048 nm

b. 0.00207 nm d. 0.00017 nm

14. Examine the following figure. Select the letter that best illustrates a blackbody that would appear red and produce no ultraviolet light.

a.

b.

c.

d.

e.

15. According to the conservation of angular momentum, if an ice-skater starts spinning with her arms out wide, then slowly pulls them close to her body, this will cause her to

a. spin faster. c. maintain a constant rate of spin.

b. spin slower. d. fall over.

16. What conservation law explains why the skater spins faster when her arms are pulled in?

a. conservation of charge c. conservation of angular momentum

b. conservation of energy d. conservation of mass

17. What quantities are needed to compute angular momentum for an object orbiting a star?

a. mass and velocity of the object

b. mass and radial distance of rotation of the object

c. velocity and radial distance of rotation of the object

d. mass, velocity, and radial distance of the object

18. According to the law of conservation of angular momentum, how would the angular velocity of a particle change if it were moved inward to half of the original distance from the center? Assume the particle is part of an accretion disk.

a. no change c. two times faster

b. half as fast d. four times faster

19. How much material in an accretion disk goes into forming the planets, moons, and smaller objects?

a. all of it c. about half of it

b. most of it d. very little of it

20. What is directly responsible for the initial development of planetesimals in an accretion disk?

a. gravity from larger particles c. collisions between dust grains

b. gravity from the protostar d. conservation of angular momentum

21. What is primarily responsible for the continued growth of kilometer-sized planetesimals in an accretion disk?

a. gravity sweeps up more material c. continued collisions with dust grains

b. static electricity attracts particles d. conservation of angular momentum

22. Conservation of angular momentum slows a cloud’s collapse

a. equally in all directions.

b. only when the cloud is not rotating initially.

c. mostly along directions perpendicular to the cloud’s axis of rotation.

d. mostly at the poles that lie along the cloud’s axis of rotation.

23. The solid form of a volatile material is generally referred to as

a. a metal. c. rock.

b. a silicate. d. ice.

24. Volatile and refractory materials differ in their

a. melting temperatures. c. composition.

b. density at a given temperature. d. All of these are correct.

25. Which of the following is a volatile material?

a. water c. iron

b. silicates d. carbon

26. Which of the following is a refractory material?

a. water c. silicates

b. methane d. ammonia

27. Whether or not a planet is composed mostly of rock or gas is set by

a. its mass.

b. its surface temperature.

c. the distance from the star it orbits when it forms.

d. All of these are correct.

28. The primary atmospheres of the planets are made mostly of

a. carbon and oxygen. c. iron and nickel.

b. hydrogen and helium. d. nitrogen and argon.

29. Which of these planets still carries a primary atmosphere since its original formation?

a. Venus c. Saturn

b. Earth d. Mars

30. Comets and asteroids are

a. other names for moons of the planets.

b. primarily located within 1 astronomical unit (AU) of the Sun.

c. all more massive than Earth’s Moon.

d. material left over from the formation of the planets.

31. The Moon probably formed

a. when the accretion disk around Earth fragmented.

b. when the Earth’s gravity captured a planetesimal.

c. out of a collision between Earth and a Mars-sized object.

d. when planetesimals collided to form a more massive object.

32. The difference in composition between the giant planets and the terrestrial planets is most likely caused by the fact that

a. the giant planets are much larger.

b. only the terrestrial planets have iron cores.

c. the terrestrial planets are formed closer to the Sun.

d. the giant planets are made mostly of carbon.

33. Which of the following is considered evidence of cataclysmic impacts in the history of our Solar System?

a. Uranus is “tipped over” so that it rotates on its side.

b. Io’s lack of water

c. Mercury’s lack of an atmosphere

d. The Moon’s lack of an atmosphere

34. Two competing models of the formation of giant gaseous planets suggest they form either from gas accreting onto a rocky core or from

a. fragmentation of the accretion disk surrounding the protostar.

b. the merger of two large planetesimals.

c. an eruption of material from the protostar.

d. materials condensing out of the solar wind.

35. During the formation of the planets, __________ energy was converted into __________ energy.

a. nuclear; thermal c. thermal; gravitational

b. thermal; nuclear d. gravitational; thermal

36. Why are most of the planets composed of refractory materials found in the inner Solar System?

a. Refractory material existed only in the inner protoplanetary disk.

b. Planetary bodies can only be formed from refractory materials.

c. The temperature of the inner protostellar accretion disk was too high for volatile components to remain solid.

d. All the bodies composed of refractory materials in the outer disk migrated to the inner disk.

37. Examine the following figure. What method of looking for extrasolar planets requires the planet to pass in front of the star?

a. radial velocity method c. direct imaging

b. transit method d. astrometry

38. The Doppler shift can be used to determine the __________ of an object.

a. energy c. radial velocity

b. temperature d. radiation

39. Astronomers hypothesize that the “hot Jupiters” found orbiting other stars must have migrated inward over time by

a. transferring orbital angular momentum.

b. colliding with another planet.

c. slowly accreting large amounts of gas and increasing their gravitational pull.

d. losing their gas because of evaporation.

40. An observer outside our Solar System who monitors the velocity of our Sun over time will find that its velocity varies by 12 meters per second (m/s) over a period of 12 years because of

a. Jupiter’s gravitational pull. c. convection on the Sun’s surface.

b. Earth’s gravitational pull. d. the sunspot cycle.

41. Why have astronomers found more Jupiter-sized planets at a distance of 1 AU around other stars than Earth-sized planets using the radial velocity method?

a. A Jupiter-sized planet occults a larger area than an Earth-sized planet.

b. A Jupiter-sized planet exerts a larger gravitational force on the star than an Earth-sized planet, and the Doppler shift of the star is larger.

c. A Jupiter-sized planet shines brighter than an Earth-sized planet.

d. Earth-sized planets are much rarer than Jupiter-sized planets.

42. Detecting a planet around another star using the transit method is difficult because

a. the planet must pass directly in front of the star.

b. the planet must have a rocky composition.

c. the star must be very dim.

d. the star must be moving with respect to us.

43. Astronomers have used radial velocity monitoring to discover

a. extrasolar planetary systems that are similar to our own Solar System.

b. Earth-sized planets around other stars.

c. Earth-sized planets at distances of 10 AU from their parent stars.

d. extrasolar planetary systems with close giant planets.

44. Which method of detecting extrasolar planets involves measuring the changing position of its host star?

a. transit c. direct imaging

b. microlensing d. astrometry

45. Which method of detecting extrasolar planets involves measuring the slight brightening of its host star?

a. radial velocity c. gravitational lensing

b. transit d. astrometry

46. Which extrasolar planet was the first directly imaged in visible light?

a. 51 Pegasi b c. Fomalhaut b

b. HR8700 b d. TRAPPIST-1b

47. When astronomers began searching for extrasolar planets, they were surprised to discover Jupiter-sized planets much closer than 1 AU to their parent stars. Why is this surprising?

a. These planets must have formed at larger distances from their parent star where temperatures were cooler and then migrated inward.

b. Jupiter-sized, rocky planets were thought to be uncommon in other solar systems.

c. These planets must be the remnants of failed stars.

d. Earth-like planets must be rarer than Jupiter-sized planets in other solar systems.

48. What is the best method commonly used to detect Earth-sized extrasolar planets with the telescopes and instrumentation that exist today?

a. Doppler shift c. direct imaging

b. transit d. microlensing

49. You record the spectrum of a star and find that the calcium absorption line, whose rest wavelength is 393.3 nm, has an observed wavelength of 394.0 nm. What is the approximate radial velocity of this star?

a. 500 kilometers per second (km/s) c. 5 km/s

b. 50 km/s d. 0.5 km/s

50. You are driving on the freeway when a police officer records a shift of -7 nm for the reflected radar beam that emanates from your car with a rest wavelength of 0.1 m. How fast were you going?

a. 47 m/s c. 21 m/s

b. 83 m/s d. 65 m/s

1. Explain the process of protostar formation shown in the following figure.

2. How does gravitational energy get converted to thermal energy in a gas cloud?

3. What does conservation of angular momentum mean?

4. Explain why an ice-skater spins faster when she pulls her arms in compared with when her arms are stretched straight out.

5. Explain why an accretion disk forms around a protostar when an interstellar cloud collapses.

6. Examine the following figure. Describe the conservation laws at play during the formation of a protostar and the accretion disk.

7. What is the difference between refractory and volatile materials?

8. What processes contributed to the development of Earth’s secondary atmosphere?

9. Explain the two primary reasons why the inner solar nebula was hotter than the outer solar nebula.

10. Why might a newly discovered comet contain clues to the composition of the early solar nebula?

11. How do astronomers explain the basic difference in composition between the inner planets and the outer planets?

12. Explain why Jupiter’s moon Io has no water.

13. The primordial atmosphere of Earth consisted of what type of chemical elements, and from where did it originate? What chemical elements did the secondary atmosphere of Earth consist of, and from where did it originate?

14. What two terrestrial-like objects in the inner Solar System do not have atmospheres and why?

15. Describe the types of exoplanets that were found early on compared to those that are now being found in abundance, and how is this related to the way in which we detect them?

16. Explain how the extrasolar planets called hot Jupiters came to exist.

17. Consider the following figure and explain how astronomers use the Doppler effect to detect the presence of extrasolar planets.

18. Briefly explain the five different observational methods we use to detect extrasolar planets.

19. Consider the following image. Describe which discovery method is being used and explain the difficulties in confirming these objects as exoplanets.

20. For a star that lies in the plane of Earth’s orbit around the Sun, how does the observed wavelength of a hydrogen absorption line in its spectrum change in wavelength (if at all) with the time of year?

21. Suppose you observe a star emitting a certain emission line of helium at 584.8 nm. The rest wavelength of this line is 587.6 nm. How fast is the star moving? Is it moving toward you or away from you?