Astron.Exam#3 – Flashcards
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Why do we call dark matter "dark"?
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C. it emits no or very little radiation of any wavelength
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What Is meant by "dark energy"?
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C. the agent causing the universal expansion to accelerate
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Why do we believe 90 percent of the mass of the milky way is in the form of dark matter?
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A. the orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo
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The distribution of the dark matter in a spiral galaxy is
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B. approximately spherical and about ten times the size of the galaxy halo
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Gravitational lensing occurs when
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A. massive objects bend light beams that are passing nearby
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Which of the following is not evidence for dark matter?
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E. the expansion of the universe
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Why isn't space expanding within systems such as our solar system or the milky way?
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D. their gravity is strong enough to hold them together against the expansion of the universe
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What does the universe look like on very large scales?
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C. galaxies appear to be distributed in chains and sheets that surround great voids
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If all the "dark matter" in the universe were to be, somehow, instantaneously removed, which of the following would not happen?
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A. the solar system would fly apart
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Recent measurements of the expansion rate of the universe reveal that expansion rate of the universe...
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C. the measurements show that the expansion is accelerating, rather than slowing under the influence of gravity
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Compared to spiral galaxies, elliptical galaxies are
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A. redder and rounder
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The disk component of a spiral galaxy includes which of the following parts?
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C. spiral arms
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Which of the following types of galaxies are most commonly found in large clusters?
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B. ellipticals
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Which of the following is true about irregular galaxies?
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C. they were more common when the universe was younger
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Why are cepheid variables important?
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Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities. Hence...
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What is Hubble's Law?
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B. The recession velocity of a galaxy is a directly proportional to its distance from us
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What makes white dwarf supernovae good standard candles?
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E. both A and B
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What is the most accurate way to determine the distance to a nearby star?
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B. stellar parallax
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Based on current estimates of the value of Hubble's constant, how old is the universe?
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C. between 12 and 16 billion years old
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Why can't we see past the cosmological horizon?
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B. beyond the cosmological horizon, we are looking back to a time before the universe had formed
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How do observations of distant galaxies help us learn about galaxy evolution?
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A. observations at different distances show galaxies of different ages and therefore different stages of evolution
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I observe a galaxy that is 100 million light-years away: what do I see?
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D. the light from the galaxy as it was 100 million years ago and it is redshifted
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Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
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B. a dense cloud with very little angular momentum
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Why should galaxy collisions have been more common in the past than they are today?
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C. galaxies were closer together in the past because the universe was smaller
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What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
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E. all of the above
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How many more stars does a starburst galaxy form, in one year, than the Milky way?
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B. about a hundred
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Starburst galaxies produce most of their light in the wavelength range of
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D. the infrared
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What is a quasar?
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D. the extremely bright center of a galaxy, thought to be powered by a massive black hole
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Which of the following is evidence for supermassive black holes in active galaxies?
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E. all of the above
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How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
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D. by gravity,...
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How long after the big bang was the planck time, before which our current theories are completely unable to describe conditions in the universe?
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C. 10^-43 second
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A GUT (grand unified theory) refers to theories
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D. unify the strong force and the electromagnetic and weak forces
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What do we mean by inflation?
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B. a sudden expansion of the universe after the strong force froze out from the GUT force
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(From a science quiz that appeared in the weekly magazine the economist)
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A. first there was a big bang, then inflation (of space) caused recession (of all matter, away from the big bang)
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What kinds of atomic nuclei formed during the era of nucleosynthesis?
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C. hydrogen and helium and trace amounts of deuterium and lithium
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Why is the era of nucleosynthesis so important on determining the chemical composition of the universe?
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C. except for the small amount of matter produced later by stars, the chemical composition of the universe is the same now as at the end...
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Why did the era of nuclei end when the universe was about 300,000 yrs old?
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B. the universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form
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Which of the following statements about the cosmic background radiation is not true?
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B. it is the result of a mixture of radiation from many independent sources, such as stars and galaxies
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What are two key observational facts that led to widespread acceptance of the big bang model?
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A. the cosmic background radiation and the high helium content of the universe
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Olber's paradox is an apparently simple question, but its resolution suggests that the universe is finite...
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D. why is the sky dark at night?
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What kinds of objects lie in the halo of our galaxy?
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C. globular clusters
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What makes up the interstellar medium?
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D. gas and dust
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How does the interstellar medium obscure our view of most of the galaxy?
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D. it absorbs visible, ultraviolet and some infrared light
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What do astronomers consider heavy elements?
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E. all elements besides hydrogen and helium
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Where are most heavy elements made?
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B. in stars and supernovae
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Suppose you read somewhere that 10% of the matter in the milky way is in the form of dust grains. Should you be surprised? if so, why?
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D. the 10% figure cannot be correct,...
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The image of our galaxy in radio emission from CO, mapping the distribution of molecular clouds, is closest to the image of our galaxy in
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E. infrared emission from interstellar dust grains
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Compared with stars in the disk, orbits of stars in the halo
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B. are elliptical, with random orientation
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How do we know that spheroidal stars are older, on average, than disk stars?
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B. there are no blue spheroidal stars
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What evidence supports the theory that there is a black hole at the center of our galaxy?
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C. the motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across
