Quiz
TB16
Crie uma conta grátis para terminar este quiz
Salve seu progresso e veja sua nota final.
Já tem uma conta? Inicie sessão
Perguntas do quiz (40)
11) Astronomers estimate that new stars form in our galaxy at the rate of about
- AA) one per year.
- BB) a few (2-3) per year.
- CC) ten per year.
- DD) 20-30 per year.
- EE) 100 per year.
22) By mass, the interstellar medium in our region of the Milky Way consists of
- AA) 70% Hydrogen, 30% Helium.
- BB) 70% Hydrogen, 28% Helium, 2% heavier elements.
- CC) 70% Hydrogen, 20% Helium, 10% heavier elements.
- DD) 50% Hydrogen, 50% Helium.
- EE) 50% Hydrogen, 30% Helium, 20% heavier elements.
33) What percentage of a molecular cloud's mass is interstellar dust?
- AA) 1%
- BB) 2%
- CC) 28%
- DD) 50%
- EE) 1-50%, depending on the mass of the molecular cloud
44) The typical density and temperature of molecular clouds are
- AA) 100 molecules per cubic centimeter, 10-30 Kelvin.
- BB) 300 molecules per cubic centimeter, 10-30 Kelvin.
- CC) 1000 molecules per cubic centimeter, 10-30 Kelvin.
- DD) 100 molecules per cubic centimeter, 100-300 Kelvin.
- EE) 300 molecules per cubic centimeter, 100-300 Kelvin.
55) The most abundant molecule in molecular clouds is
- AA) H2.
- BB) He2.
- CC) CO.
- DD) H2O.
- EE) HHe.
66) The typical size of an interstellar dust grain is
- AA) 1 angstrom.
- BB) 1 nanometer.
- CC) 1 micrometer.
- DD) 1 millimeter.
- EE) 1 centimeter.
77) What is interstellar reddening?
- AA) Interstellar dust absorbs more red light than blue light, making stars appear redder than their true color.
- BB) Interstellar dust absorbs more red light than blue light, making stars appear bluer than their true color.
- CC) Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.
- DD) Interstellar dust absorbs more blue light than red light, making stars appear bluer than their true color.
- EE) The spectral line shift due to a star's motion through the interstellar medium.
88) If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe?
- AA) ultraviolet
- BB) visible
- CC) infrared
- DD) X-ray
- EE) gamma-ray
99) What happens to the visible radiation produced by new stars within a molecular cloud?
- AA) It escapes the cloud completely.
- BB) It is absorbed by dust grains and heats up the cloud.
- CC) It is reflected back onto the protostar, heating it up further.
- DD) The blue light is absorbed and the red light transmitted.
- EE) It shoots out in bright jets.
1010) The thermal pressure of a gas depends on
- AA) density only.
- BB) temperature only.
- CC) density and temperature.
- DD) composition.
- EE) gravity.
1111) The gravitational force in a molecular cloud depends on
- AA) density only.
- BB) temperature only.
- CC) density and temperature.
- DD) composition.
- EE) thermal pressure.
1212) What prevents the pressure from increasing as a cloud contracts due to its gravity?
- AA) As the cloud becomes denser, gravity becomes stronger and overcomes the pressure buildup.
- BB) The pressure is transferred from the center of the cloud to its outer edges where it can dissipate.
- CC) Thermal energy is converted to radiative energy via molecular collisions and released as photons.
- DD) Excess pressure is released in jets of material from the young stars.
- EE) Once the cloud reaches a critical density, the pressure becomes degenerate and independent of temperature.
1313) Calculations show that gravity begins to overcome thermal pressure in clouds that are
- AA) less massive than the Sun.
- BB) more massive than the Sun.
- CC) more massive than ten times the Sun.
- DD) more massive than a hundred times the Sun.
- EE) more massive than a thousand times the Sun.
1414) What property of a molecular cloud does not counteract gravitational contraction?
- AA) thermal pressure
- BB) turbulent motions
- CC) magnetic fields
- DD) fragmentation
1515) How do astronomers infer the presence of magnetic fields in molecular clouds?
- AA) by measuring the amount of interstellar reddening
- BB) by measuring the Doppler shifts of emission lines from gas clumps in the cloud
- CC) by measuring the infrared light emitted by the cloud
- DD) by measuring the polarization of starlight passing through the cloud
- EE) by measuring the amount by which gravity is reduced
16
16) What is the likely reason that we cannot find any examples of the first generation stars?- AA) The first generation stars are too faint to be visible now.
- BB) The first generation stars formed such a long time ago that the light from them has not yet had time to reach us.
- CC) The first generation stars were all very massive and exploded as supernova.
- DD) The first generation stars formed with only H and He and therefore have no spectral features.
- EE) We do not know how the first generation stars were formed.
1717) Why do we think the first generation of stars would be different from stars born today?
- AA) Without heavy elements, the clouds could not reach as low a temperature as today and had to be more massive to collapse.
- BB) Without heavy elements, the nuclear reactions at the center of the stars would be very different.
- CC) Without heavy elements, there was no dust in the clouds and they collapsed faster.
- DD) The Universe was much denser when the first stars were born.
- EE) There were no galaxies when the first stars were born.
1818) What is the minimum temperature for a cloud to excite emission lines from H2?
- AA) 10 K
- BB) 30 K
- CC) 100 K
- DD) 300 K
- EE) 1000 K
1919) When is thermal energy trapped in the dense center of a cloud?
- AA) when the gravity becomes so strong that photons cannot escape
- BB) when excited molecules collide with other molecules before they can release a photon
- CC) when the cloud becomes so hot and dense that nuclear fusion begins
- DD) when magnetic fields trap the radiation
- EE) when the cloud cools down so much that less light escapes than is produced by contraction
2020) What happens to the rotation of a molecular cloud as it collapses to form a star?
- AA) The rotation rate remains the same and results in stellar rotation.
- BB) The rotation dissipates and any residual is left in small overall rotation of the star.
- CC) The rotation rate increases and results in fast rotation of the star.
- DD) The rotation rate increases and results in a disk of material around a protostar.
- EE) The rotation increases the speed of collapse and produces more massive stars.
2121) Which of the following may be caused by a protostellar disk?
- AA) protostellar jets
- BB) protostellar winds
- CC) accretion of material onto the star
- DD) relatively slow protostellar rotation
- EE) all of the above
2222) When does a protostar become a true star?
- AA) when the star is 1 million years old
- BB) when the central temperature reaches 1 million Kelvin
- CC) when nuclear fusion begins in the core
- DD) when the thermal energy becomes trapped in the center
- EE) when the stellar winds and jets blow away the surrounding material
2323) How long does the protostellar stage last for a star like our Sun?
- AA) 1 million years
- BB) 3 million years
- CC) 10 million years
- DD) 30 million years
- EE) 100 million years
2424) What is the range of timescales for star formation?
- AA) from 1 million years for the most massive stars up to 10 million years for the least massive stars
- BB) from 1 million years for the most massive stars up to 100 million years for the least massive stars
- CC) from 1 million years for the least massive stars up to 10 million years for the most massive stars
- DD) from 1 million years for the least massive stars up to 100 million years for the most massive stars
- EE) about 30 million years for all stars, whatever mass
2525) What species absorbs photons in a protostar's outer layers?
- AA) H
- BB) H2
- CC) H+
- DD) H-
- EE) dust
2626) When does a star become a main-sequence star?
- AA) when the protostar assembles from a molecular cloud
- BB) the instant when hydrogen fusion first begins in the star's core
- CC) when the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium
- DD) when a star becomes luminous enough to emit thermal radiation
- EE) when hydrogen fusion is occurring throughout a star's interior
2727) What happens to the surface temperature and luminosity when gravity first assembles a protostar from a collapsing cloud?
- AA) Its surface temperature and luminosity increase.
- BB) Its surface temperature remains the same and its luminosity decreases.
- CC) Its surface temperature and luminosity decrease.
- DD) Its surface temperature decreases and its luminosity increases.
- EE) Its surface temperature and luminosity remain the same.
2828) What happens to the surface temperature and luminosity when a protostar undergoes convective contraction?
- AA) Its surface temperature and luminosity increase.
- BB) Its surface temperature remains the same and its luminosity decreases.
- CC) Its surface temperature and luminosity decrease.
- DD) Its surface temperature decreases and its luminosity increases.
- EE) Its surface temperature and luminosity remain the same.
2929) What happens to the surface temperature and luminosity when a protostar radiatively contracts?
- AA) Its surface temperature and luminosity increase.
- BB) Its surface temperature remains the same and its luminosity decreases.
- CC) Its surface temperature and luminosity decrease.
- DD) Its surface temperature decreases and its luminosity increases.
- EE) Its surface temperature and luminosity remain the same.
3030) When does hydrogen first begin to fuse into helium in the star formation process?
- AA) when the cloud first begins to contract
- BB) when the thermal pressure is trapped at the center of the cloud
- CC) when the protostars undergoes convective contraction
- DD) when the protostar undergoes radiative contraction
- EE) only when the star reaches the main-sequence
3131) About how many times more luminous than our Sun is a young solar mass protostar just beginning convective contraction?
- AA) 2-5
- BB) 5-10
- CC) 10-100
- DD) 100-1000
- EE) a million
3232) What is the smallest mass a newborn star can have?
- AA) 8 times the mass of Jupiter
- BB) 80 times the mass of Jupiter
- CC) 800 times the mass of Jupiter
- DD) about 1/80 the mass of our Sun
- EE) about 1/800 the mass of our Sun
3333) What are the letters that follow the spectral sequence OBAFGKM?
- AA) NP
- BB) YZ
- CC) LT
- DD) CD
- EE) UV
3434) What is the greatest mass a newborn star can have
- AA) 10 solar masses.
- BB) 20 solar masses.
- CC) 50 solar masses.
- DD) 150 solar masses.
- EE) 300 solar masses.
3535) No stars have been found with masses greater than 300 times our Sun because
- AA) molecular clouds do not have enough material to form such massive stars.
- BB) they would fragment into binary stars because of their rapid rotation.
- CC) they would generate so much power that they would blow themselves apart.
- DD) they shine exclusively at X-ray wavelengths and become difficult to detect.
- EE) they are not bright enough to be seen nearby.
3636) For every star with a mass greater than 10 solar masses, about how many stars are there with masses less than a solar mass?
- AA) 1
- BB) 3
- CC) 10
- DD) 30
- EE) 200
3737) Which of the following discoveries, if they existed, would necessitate a reevaluation of our ideas of stellar formation?
- AA) a cluster of stars that appeared to be 13 billion years old
- BB) a 100-solar-mass star
- CC) a 0.01-solar-mass star
- DD) a molecular cloud without any stars
- EE) planetary systems around other stars than our own
3838) What prevents a brown dwarf from undergoing nuclear fusion?
- AA) Degeneracy pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.
- BB) There is not enough mass to maintain nuclear reactions in a self-sustaining way.
- CC) The surface temperature never rises high enough for the radiation to be trapped and heat their interior to the temperatures required for nuclear fusion.
- DD) Radiation pressure halts the contraction of a protostar so the core never becomes hot or dense enough for nuclear fusion.
- EE) There are too many heavy elements and not enough hydrogen for fusion to occur in a self-sustaining way.
3939) What is the eventual fate of a brown dwarf?
- AA) It remains the same forever.
- BB) It gradually cools down and becomes ever dimmer.
- CC) It gradually contracts and heats up until nuclear fusion ignites in its interior and it becomes a faint star.
- DD) It becomes ever denser and hotter until it becomes a white dwarf.
- EE) Gravity ultimately "wins" and it becomes a small black hole.
4040) Where would a brown dwarf be located on an H-R diagram?
- AA) upper right
- BB) on the lower part of the main sequence
- CC) below and to the right of the lowest part of the main sequence
- DD) lower left
- EE) above and to the left of the main sequence
Informações
- Descrição
- 1 astro (Astro Testbank 16) Quiz sobre TB16, criado por Jianxiong Ng em 23-03-2016.
- Autor
- Jianxiong Ng
- Idioma
- English
- Visualizações
- 0
- Histórico
- Criado em 23 mar 2016 · atualizado em 31 mar 2016
- Etiquetas
- Avaliação
- Ainda sem avaliações Avalie este quiz