Exam 3 Practice Quiz – Flashcards
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Based on Kepler's Law another star in our Galaxy, closer to the Galactic center than the Sun, will revolve around that center
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faster than the Sun (shorter period)
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Which of the following observations confirms that the object named "Sgr A*" at the center of our galaxy is indeed a supermassive black hole?
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Measurements of the orbits of stars around Sgr A*
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Galaxy mergers
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are thought to be an important part of the formation of galaxies.
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Which of these is NOT a reasonable explanation for the dark matter data in galaxies and clusters?
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We have underestimated the distances to galaxies by 10x, which means the galaxies are about 10x bigger (more massive) than we thought, avoiding the need for dark matter altogether.
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What is a quasar?
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the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole
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A spiral density wave in a Galaxy refers to
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a slight "bunching together" of the stars and gas in the spiral arms of a disk galaxy, causing a large increase in the local star formation rate.
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The cosmic microwave background refers to
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The leftover radiation from the Big Bang, last emitted at the end of the era of nuclei, and redshifted into the microwave part of the electromagnetic spectrum.
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In spiral galaxies, why do the spiral arms appear brighter than the areas between the arms?
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There are more very bright stars in the spiral arms because they are formed there and are short lived, so they never move out of the spiral arms.
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If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for___________.
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how galaxies came to exist
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When a star is gravitationally lensed by a foreground object, the star appears
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brighter
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The best evidence for a small but super-massive object at the center of our Galaxy is from
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use of Kepler's Third Law for the orbits of stars, seen in very high-resolution infrared images around Sgr A*.
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What kind of Galaxy is the Milky Way?
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A barred spiral galaxy.
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The Fermi paradox, named after the early 20th century physicist Enrico Fermi, refers to
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his question "Where are they?" about the lack of evidence for extraterrestrial civilizations.
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How do observations of galaxies at different distances help us learn about galaxy evolution?
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Observations of different distances show galaxies of different ages and therefore different stages of evolution.
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The Milky Way has a "rotation curve" which
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rises rapidly at first, but is then constant as far out as we can measure.
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How do we learn about the conditions at the center of our own galaxy, the Milky Way?
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While we cannot see the galactic center with visible light, we can detect radio, infrared, and X-rays from the center use that information to determine the conditions there.
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The most luminous type of active galaxy is the
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quasar
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Which of the following is a consequence of Hubble's Law?
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the more distant a galaxy is from us, the faster it moves away from us
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Powerful jets coming from active galactic nuclei are sometimes seen to fly away from their driving source at apparent speeds much faster than light. This is due to
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a relativistic illusion.
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Which of the following best summarizes what we mean by dark energy?
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It is a name given to whatever is causing the expansion of the universe to accelerate with time.
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Dark energy is probably made up of
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a phenomenon that may be revealed by a good enough theory of quantum
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Why isn't the space within our solar system or the Milky Way expanding according to Hubble's Law?
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The gravity exerted by the solar system and the Milky Way is strong enough to hold them together against the expansion of the universe.
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The rotation curve (rotation velocity vs. distance from center) for objects in our Galaxy
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is flat and remains flat at radii beyond the visible edge of the Galaxy indicating that significant dark matter is present.
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How was Edwin Hubble able to use his discovery of Cepheid variables in Andromeda to prove that the "spiral nebulae" were actually galaxies external to the Milky Way?
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From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda. He showed that it was far outside the Milky Way Galaxy.
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What evidence do we have for the existence of "dark energy"?
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The expansion of the universe is accelerating
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If we make the simple assumption that the current expansion rate of the universe has and will remain constant, what is the age of the universe?
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14 billion years
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Why did astronomers of the year 1900 greatly underestimate the size of the galaxy?
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they were unaware of the existence of interstellar dust
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Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the simple question posed by Olbers' paradox?
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Why is the sky dark at night?
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What is the age distribution observed for stars in various regions of our galaxy?
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Most stars in the disk are younger than stars in the halo.
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Which type of galaxy contains the least amount of interstellar material?
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ellipticals
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What aspects of the Universe were originally unexplained by the Big Bang model?
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~~ All of these features. ~~ The origin of the density enhancements that turned into galaxies and larger structures. You Answered The overall smoothness of the Universe on large scales. The measured density of the Universe being close to the critical value. Correct Answer Only the smoothness and density aspects.
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Elliptical galaxies
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have no obvious galactic disk and contain mostly old, halo-type stars.
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Which of the following is a false statement about the cosmic microwave background?
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It was discovered by theoretical physicists at Princeton.
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The Tully-Fisher relationship is a relationship between
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galaxy rotation speed and luminosity
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Many large clusters of galaxies contain a lot of ellipticals and few spirals, while smaller clusters of galaxies contain few elliptical and more spirals. Why do we think this happens?
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Galaxy collisions, which tend to strip gas from spirals, are more common in large clusters.
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Elliptical galaxies
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have no obvious galactic disk and contain mostly old, halo-type stars.
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Some regions along the plane of the Milky Way appear dark because
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stars in that region are hidden by dark dust clouds.
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If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for___________.
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how galaxies came to exist
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Hubble's constant is a number that relates
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a galaxy's redshift to its distance.
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What is a quasar?
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the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole
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Is space within clusters of galaxies expanding according to Hubble's law?
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No, because their gravity is strong enough to hold them together even while the universe as a whole expands.
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Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
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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 most luminous type of active galaxy is the
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quasar
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The lookback time to a distant galaxy refers to
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the time taken for the photons we are now receiving from the galaxy to reach us, given its distance.
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If we make the simple assumption that the current expansion rate of the universe has and will remain constant, what is the age of the universe?
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14 billion years
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The GUT force in the early Universe operated as a unification of the ______________ forces at high temperatures.
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strong and electroweak
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What did Carl Sagan mean when he said that we are all "star stuff"?
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that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores
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Collisions between galaxies are expected to be more common than collisions between stars because
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Relative to their size, galaxies are much closer together than stars are.
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Is space within clusters of galaxies expanding according to Hubble's law?
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No, because their gravity is strong enough to hold them together even while the universe as a whole expands.
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Which type of galaxy contains the least amount of interstellar material?
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ellipticals
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The cosmic microwave background refers to
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The leftover radiation from the Big Bang, last emitted at the end of the era of nuclei, and redshifted into the microwave part of the electromagnetic spectrum.
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How do we learn about the conditions at the center of our own galaxy, the Milky Way?
answer
While we cannot see the galactic center with visible light, we can detect radio, infrared, and X-rays from the center use that information to determine the conditions there.
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Many large clusters of galaxies contain a lot of ellipticals and few spirals, while smaller clusters of galaxies contain few elliptical and more spirals. Why do we think this happens?
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Galaxy collisions, which tend to strip gas from spirals, are more common in large clusters.
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What aspects of the Universe were originally unexplained by the Big Bang model?
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~~ All of these features. ~~ Only the smoothness and density aspects. The origin of the density enhancements that turned into galaxies and larger structures. The measured density of the Universe being close to the critical value. The overall smoothness of the Universe on large scales.
question
A spiral density wave in a Galaxy refers to
answer
a slight "bunching together" of the stars and gas in the spiral arms of a disk galaxy, causing a large increase in the local star formation rate.
question
How was Edwin Hubble able to use his discovery of Cepheid variables in Andromeda to prove that the "spiral nebulae" were actually galaxies external to the Milky Way?
answer
From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda. He showed that it was far outside the Milky Way Galaxy.
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What is the primary evidence that has led astronomers to conclude that the expansion of the universe is accelerating?
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Observations of white dwarf supernovae
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How can we tell the age of the universe?
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by using the inverse of the Hubble?s constant
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Which of these things is much more concentrated in a spiral arm than in the general disk population of a spiral galaxy?
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Giant molecular clouds and large HII regions.
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What kind of Galaxy is the Milky Way?
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A barred spiral galaxy.
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How do observations of galaxies at different distances help us learn about galaxy evolution?
answer
Observations of different distances show galaxies of different ages and therefore different stages of evolution.
question
The lookback time to a distant galaxy refers to
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the time taken for the photons we are now receiving from the galaxy to reach us, given its distance.
question
The rotation curve (rotation velocity vs. distance from center) for objects in our Galaxy
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is flat and remains flat at radii beyond the visible edge of the Galaxy indicating that significant dark matter is present.
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Which kind of star is highly UNLIKELY to be found in the halo of the Milky Way?
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O star
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When a star is gravitationally lensed by a foreground object, the star appears
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brighter
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In spiral galaxies, why do the spiral arms appear brighter than the areas between the arms?
answer
There are more very bright stars in the spiral arms because they are formed there and are short lived, so they never move out of the spiral arms.
question
Which of the following observations confirms that the object named "Sgr A*" at the center of our galaxy is indeed a supermassive black hole?
answer
Measurements of the orbits of stars around Sgr A*
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Which of the following best summarizes what we mean by dark energy?
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It is a name given to whatever is causing the expansion of the universe to accelerate with time.
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Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
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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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How can we tell the age of the universe?
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by using the inverse of the Hubble?s constant
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The Tully-Fisher relationship is a relationship between
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galaxy rotation speed and luminosity
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Why did astronomers of the year 1900 greatly underestimate the size of the galaxy?
answer
they were unaware of the existence of interstellar dust
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Which kind of star is highly UNLIKELY to be found in the halo of the Milky Way?
answer
O star
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The Milky Way has a "rotation curve" which
answer
rises rapidly at first, but is then constant as far out as we can measure.
question
Which of these things is much more concentrated in a spiral arm than in the general disk population of a spiral galaxy?
answer
Giant molecular clouds and large HII regions.
question
If observations had shown that the cosmic microwave background was perfectly smooth (rather than having very slight variations in temperature), then we would have no way to account for___________.
answer
how galaxies came to exist
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Where does most star formation occur in the Milky Way today?
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in the spiral arms
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Some regions along the plane of the Milky Way appear dark because
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stars in that region are hidden by dark dust clouds.
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Elliptical galaxies
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have no obvious galactic disk and contain mostly old, halo-type stars.
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Which type of galaxy contains the least amount of interstellar material?
answer
ellipticals
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The Cosmological Principle states that
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the universe is homogeneous and isotropic on sufficiently large scales
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Which of these is NOT a reasonable explanation for the dark matter data in galaxies and clusters?
answer
We have underestimated the distances to galaxies by 10x, which means the galaxies are about 10x bigger (more massive) than we thought, avoiding the need for dark matter altogether.
question
Which of the following best summarizes what we mean by dark energy?
answer
It is a name given to whatever is causing the expansion of the universe to accelerate with time.
question
What kind of Galaxy is the Milky Way?
answer
A barred spiral galaxy.
question
Dark energy is probably made up of
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a phenomenon that may be revealed by a good enough theory of quantum
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The GUT force in the early Universe operated as a unification of the ______________ forces at high temperatures.
answer
strong and electroweak
question
Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the simple question posed by Olbers' paradox?
answer
Why is the sky dark at night?
question
What evidence do we have for the existence of "dark energy"?
answer
The expansion of the universe is accelerating
question
Which of the following observations confirms that the object named "Sgr A*" at the center of our galaxy is indeed a supermassive black hole?
answer
Measurements of the orbits of stars around Sgr A*
question
What is the primary evidence that has led astronomers to conclude that the expansion of the universe is accelerating?
answer
Observations of white dwarf supernovae
question
Where does most star formation occur in the Milky Way today?
answer
in the spiral arms
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Many large clusters of galaxies contain a lot of ellipticals and few spirals, while smaller clusters of galaxies contain few elliptical and more spirals. Why do we think this happens?
answer
Galaxy collisions, which tend to strip gas from spirals, are more common in large clusters.
question
Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
answer
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.
