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129 Cards in this Set
- Front
- Back
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A major discovery made by Shapley using RR Lyrae stars and globular clusters established
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The size of the galaxy and the sun's position in it.
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What type of matter is observed using radio telescopes in the mapping of the galactic structure?
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Hydrogen gas and the carbon monoxide molecule
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Where is active star formation most often found in the galaxy?
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Disk
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What events may trigger new star formation in a spiral arm?
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Compression from a density wave
Shock waves from emission nebulae Shock waves from supernovae |
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Which of the following properties of elliptical galaxies is also shared with spiral galaxies?
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Contains old stars
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Hubble's law relates which two observed properties of a galaxy?
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Distance and recessional velocity
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Once Hubble's law is established, what single observation is needed of a galaxy in order to determine its distance?
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Recessional velocity
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What is observed that connects radio emissions in the galactic nucleus with the emissions in the halo or radio lobes?
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There is a jet of matter coming out of the nucleus, which often points towards the lobes.
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Specifically, what produces the intense radiation, jets, and other features of active galaxies?
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Accretion disks which surround supermassive black holes
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Which of the following properties of quasars is common to all quasars without exception?
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High redshift
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What is the strongest piece of evidence suggesting that quasars represent an early stage of galaxy formation?
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They are all distant.
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How does the age of the universe depend on the Hubble constant?
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It is inversely proportional to it
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Which of the following is the correct interpretation of the Hubble law?
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Galaxies are not moving through space, it is space that is expanding over time.
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Where did the big bang occur?
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Everywhere
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What is the explanation for the high redshifts observed in distant objects?
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In the time it took their light to reach us, the universe expanded and, thus, their wavelengths.
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What is the origin of the cosmic microwave background?
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Light remaining from the big bang
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By the end of the nuclear epoch, some 1000 seconds after the big bang, the matter of the universe was composed of 25 percent _____ .
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Helium
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What purpose or role was played by dark matter in the early universe?
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Its density fluctuations determined the overall large-scale structure of the universe.
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What type of spectrum is the cosmic microwave background?
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Thermal radiation
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What perception of the Milky Way Galaxy did astronomers have in the early part of this century?
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They believed that the Milky Way was the entire universe.
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The location of the center of the Galaxy is determined by observations of
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Globular Clusters
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Which is the correct description of the Sun's location within the Milky Way?
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In the disk and about 2/3 of a galactic radius from the center.
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The object located at the center of the Galaxy is believed to be a
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supermassive black hole
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What property is common to almost all spiral galaxies
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Ongoing star formation
The disk, bulge, and halo Abundant interstellar gas |
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Which of the following is the Hubble Law?
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The greater the distance to a galaxy, the greater its redshift.
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What does the Hubble Law measure?
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The rate of expansion of the Universe.
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A galaxy is at a distance of one billion light years. Which of the following is true?
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We see the galaxy the way it was one billion years ago.
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Why are supermassive elliptical galaxies often found at the cores of rich galaxy clusters?
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They are the result of numerous galactic mergers--cannibalism on the largest scale.
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The look-back time of an object is directly related to its
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distance
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Why do some quasars and galaxies have redshifts greater than 1?
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They are very distant.
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Because we see the light from distant galaxies redshifted, we know that
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the Universe is expanding.
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The cosmic microwave background is important mostly because
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it confirmed a major prediction made by the Big Bang theory.
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The redshift of galaxies in the Universe is correctly interpreted as
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space itself expanding with time, stretching the wavelengths from the light.
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Why didn't an abundance of elements heavier than helium form in the early universe?
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The expansion of the Universe caused the temperature and density to drop too low for fusion to occur
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Currently, most of the mass of the Universe is believed to consist of
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dark matter.
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An astronomer needs to measure the distance to a globular cluster of stars that is part of the Milky Way. What method should she try to use?
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find an RR Lyrae variable star in the cluster
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Our Milky Way galaxy is what type of galaxy?
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spiral (barred spiral)
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Where should we look for the youngest stars in the Milky Way?
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in the spiral arms of the disk
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Globular clusters orbit the center of the Milky Way in very elliptical orbits. At any given time, where would we expect to find most of these clusters?
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In the halo, because that's where they spend the most time
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One of the most important observations in the history of astronomy was the one made by Edwin Hubble (about 1920) that established that there are other galaxies, quite removed from the Milky Way. How did Hubble show this?
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By observing a Cepheid variable in the Andromeda galaxy and using it to get the distance.
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What is the net result of the proton-proton chain of nuclear fusion?
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4 hydrogens are fused into 1 helium, 2 neutrinos + energy
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What is the critical temperature at which hydrogen can begin to fuse into helium in the core of a star?
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15 million K.
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What characteristic of a star cluster is used to determine its age?
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The position of the main sequence turnoff in the HR diagram.
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What inevitably forces a star like the Sun to evolve away from being a main sequence star?
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It builds up a core of helium.
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Which of the following is true regarding planetary nebulae?
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They are the ejected envelopes of highly evolved low-mass stars.
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What is *not* approximately the same for each star in a cluster?
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mass
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Nearly all the elements were formed inside stars. The major exception is:
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Hydrogen.
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A surface explosion on a white dwarf, caused by nuclear fusion of fallen matter from a binary companion, creates what kind of object?
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Nova.
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What is the only way that a white dwarf can suddenly explode?
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if it gains sufficient mass from a binary companion to exceed the Chandrasekhar mass
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Which star will live a longer life on the main sequence?
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A star with 0.1 times the mass of the Sun.
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Star cluster A is 10 billion years old and star cluster B is one million years old. At birth they had the same mass. Which statement is correct?
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A contains more red giant stars than B
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Type I supernovae _______
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are explosions which destroy white dwarfs
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A spectral line in a particular galaxy is observed to be at a wavelength of 5500 Angstroms instead of the normal 5000 Angstroms. How fast is the galaxy moving? (the speed of light is 300,000 km/s)
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30,000 km/s away from us
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What wavelength of electromagnetic radiation is best to study a star forming from a dense dust cloud?
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infrared
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Which of the following is NOT a characteristic of giant molecular clouds?
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simple structure
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A radio telescope with a diameter of 100m detects electromagnetic radiation with a wavelength of 1cm. Your eye sees light with a wavelength as short as 3000 Angstroms = 0.3 microns, and has a pupil diameter of 0.3cm = 3000 microns. Which can see the finer detail?
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They are equally good at resolving detail.
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Which of the following properties is NOT desirable for a good telescope?
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refracting lenses rather than reflecting mirrors
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Which of these nebulae are not associated with star-forming regions?
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planetary nebula
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What is the final fate of the Sun?
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white dwarf
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How much time does the Sun have left to shine by nuclear fusion?
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5 billion years
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What kind of pressure supports a white dwarf?
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electron degeneracy pressure
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Which of the following observations has the most light gathering power?
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1 second exposure on a 100 meter diameter telescope
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The final element produced by fusion in a massive star before it dies is
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iron
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A high-mass star dies more violently than a low-mass star because:
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It eventually produces a massive core that cannot be supported by nuclear fusion, and so collapses very rapidly.
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An iron core cannot support a star because:
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Iron cannot fuse with other nuclei to produce energy.
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The heaviest nuclei of all are formed:
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During a supernova explosion
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A star can be a supernova:
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Once.
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What is Cygnus X-1?
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a leading candidate for being a black hole
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The key to identifying a black hole candidate in a binary system is the following
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the unseen companion in the system must have a sufficiently high mass
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What do you observe if you see a clock on a VERY fast train moving by you?
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The moving clock ticks more slowly than your own clock.
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What do you observe if you see a clock that is near to a black hole?
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The clock ticks more slowly than your own clock.
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You measure the length of a stationary stick to be one meter. What do you observe if you see the same stick on a VERY fast train moving by you?
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The stick appears to be shorter.
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The measured speed of light in a vacuum
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does not depend on the inertial reference frame.
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Which of the following is not evidence in favor of General Relativity?
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The slow rotation of Venus.
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What is a pulsar?
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The remnant of some type II supernova explosions.
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What is the correct ordering from largest to smallest?
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Red giant star, white dwarf, neutron star, the Earth
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In which of the following models will the universe stop expanding?
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Closed universe.
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The cosmic microwave background is important mostly because:
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It confirmed a major prediction made by the Big Bang theory.
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The universe has three possible futures. Which one is correct depends only on the average density of matter in the universe. Why is this?
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The density of matter determines the strength of gravity, which decelerates the expansion over time.
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What is the meaning of a "closed" universe?
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The universe will someday stop expanding and start to collapse.
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The redshift of galaxies in the universe is correctly interpreted as:
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Space itself is expanding with time; the wavelengths of photon are stretched while they travel through space.
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Why didn't an abundance of elements heavier than helium form in the early universe?
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The expansion of the universe caused the temperature and density to drop too low for fusion to occur.
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Currently, most of the mass of the universe is believed to consist of:
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dark matter
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If the space of the Universe was negatively curved, then two beams of light leaving the Earth parallel to each other and heading out into space
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would get farther apart.
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When the temperature of the gases in the Universe fell sufficiently for protons and electrons to recombine to form neutral hydrogen, what cosmologically significant event occurred?
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The photons in the Universe uncoupled from the matter.
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Why should the expansion of the universe slow down with time?
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Mutual gravity between galaxies slows the expansion.
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One reason that the primeval background radiation looks like it has been emitted by a cold 3 K body is that
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we see it greatly redshifted.
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The value of the Hubble Constant
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measures the expansion rate of the Universe, and thus helps to determine its age
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Why are observations of small fluctuations in the microwave background significant?
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They show the small irregularities that gravity would act upon to form galaxies and clusters of galaxies
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Four of the following validate the Big Bang model. Which statement has no bearing on the question?
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the supermassive black hole nature of the energy source in quasars
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Dark Energy:
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is a mysterious energy source that is causing the expansion of the Universe to accelerate.
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Hubble's constant is 70 km/s per Mpc. A distant galaxy is observed to be receding from us at 1400 km/s. How far away is it?
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20 Mpc
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Astronomers believe in the existence of Dark Matter because
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the orbital velocity of stars and gas in the Milky Way are fairly constant with Galactic radius
galaxies in clusters have quite high velocities very hot gas is seen in clusters of galaxies galaxy clusters act as strong gravitational lenses |
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Which of the following is not a factor in the Drake equation for estimating the number of technological civilizations in the Galaxy?
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the number of planetary nebulae in the Galaxy
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The Big Bang theory explains
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the abundance of helium in interstellar gas
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What important molecules for life were found in the first Miller-Urey experiment?
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Amino acids.
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Which of the following factors from the Drake equation has a value which is currently well constrained?
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Rate of star formation.
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Assuming that conditions ripe for life and intelligence abound in the Galaxy, what factor limits the number of Galactic civilizations?
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The average survival time for civilizations.
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About how many extrasolar planets have been discovered to date?
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more than 300
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Most of the extrasolar planets today have been found using which of the following techniques?
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Radial Velocity/Doppler
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Which of the following exoplanets is easiest to find using the "wobble" method?
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a massive planet, close to its host star
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What perception of the Milky Way Galaxy did astronomers have at the beginning of the 20th century?
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They believed that the Sun was roughly in the center of the Milky Way.
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Harlow Shapley determined the location of the center of the Galaxy by observations of:
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Globular clusters.
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Which is the correct description of the Sun's location within the Milky Way?
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In the disc and about one-half a galactic radius from the center.
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What two observations of an object orbiting in the Milky Way allow for a determination of the Milky Way's mass?
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Object's velocity and distance from the Galactic center.
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What type of variable star is used to determine the distances to globular clusters?
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RR Lyrae stars
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Which of the following is not found in the Galaxy's halo?
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emission nebulae containing young stars
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The object located at the very center of the Galaxy is believed to be a ________.
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a black hole
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About how many galaxies are believed to exist in the observable universe?
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about 20 billion or more
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Collisions between galaxies:
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May cause bursts of star formation.
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What is the Great Wall?
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It is a large sheet of galaxies measuring 70 Mpc by 200 Mpc.
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Which of the following is the Hubble Law?
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The greater the distance to a galaxy, the greater its redshift.
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What does the Hubble Law measure?
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The rate of expansion of the universe.
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Which type of galaxy has a small bulge and loose, poorly defined spiral pattern?
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Sc
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In a radio galaxy, the ultimate energy source for the entire radio lobe source is thought to be:
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a black hole in the center of the galaxy
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Which of the following is not a characteristic of active galaxies?
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Their energy emission can be explained as the accumulated emission of billions of stars.
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Why is the energy source of Active Galactic Nuclei (AGN) thought to be extremely compact?
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They vary on rapid time scales.
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The look-back time of an object is directly related to its:
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Distance.
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What was discovered about the spectra of quasars?
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They contained normal emission lines that were highly red shifted.
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Quasars have their distances measured by what technique?
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Hubble law
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Because essentially all galaxies are redshifted, we know that:
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The universe is expanding.
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Homogeneity and isotropy, taken as assumptions regarding the structure and evolution of the universe, are known as:
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The Cosmological Principle.
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In finding the distance to a galaxy using Cepheid variables, the star's luminosity is determined
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from the period-luminosity relation.
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The center of our galaxy is in the direction of the constellation
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Sagittarius.
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What is the Local Group?
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the galaxies found with a few million lights years of us
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A nova happens in a distant galaxy. You -think- it is a supernova. How will the distance you calculate compare with the true distance?
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Your calculated distance will be larger than the true distance.
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Which of the following statements would best describe the color of an elliptical galaxy?
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Reddish, because most of the star formation was long ago and no blue stars are left.
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Which of the following type of galaxies are most similar to the Milky Way Galaxy?
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spirals
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Astronomers have found that the galaxies in clusters are moving around with unexpectedly high velocities. The explanation accepted by astronomers is that
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there is apparently much more mass in the clusters of galaxies than we have detected so far.
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