Astronomy Quiz 12 and Chapters 15, 16, & 17 HW – Flashcards
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Which of the following is NOT a distance indicator used in galactic astronomy?
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white dwarfs
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(a) Rank the subclasses of spiral galaxies in order of how tightly wound they are: Sa, Sb, Sc. (b) Rank the subclasses of spiral galaxies in order of the size of their nuclei, from smallest to largest: Sa, Sb, Sc.
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(a) most to least: Sa, Sb, Sc (b) smallest to largest: Sc, Sb, Sa
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Why is a supernova type Ia standard candle better to use in measuring very long distances than either the brightest globular cluster or Cepheid Variable star standard candles?
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Supernovae type Ia are more luminous.
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This image shows four quasars around a galaxy. The redshift of each of the four quasars is 0.0394 and greater than that of the galaxy. How should we interpret this photo?
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The galaxy acts as a gravitational lens and the four quasar images are of the same quasar.
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(a) What is the Milky Way in our sky? (b) Would people living on a planet orbiting a star in an E0 type galaxy see a Milky Way?
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(a) It is bright band of light that goes around the entire sky and it is the disk of the galaxy of which we are a part. (b) No, their galaxy has no disk.
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Which type of galaxy has the largest range in both size and mass?
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elliptical
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What did William Parsons (Lord Rosse) think the spiral nebulae were?
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island universes
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In a few billion years, our own Milky Way may merge with the Andromeda Galaxy. Which type of galaxy is most likely to result from such a merger?
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an elliptical galaxy
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The Hubble Deep Field image reveals more than 1,500 distant galaxies in a region about 1 arc minute in diameter. If this density of galaxies is typical over the whole sky, how many distant galaxies are hidden from view at one instant by our moon that has an angular diameter of about 30 arc minutes?
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More than 1,000,000 distant galaxies are hidden behind our moon at one time.
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(a) Which is a more likely evolution of galaxies? (b) What is the most likely way that one type of galaxy may be formed from others? (c) What type of galaxy is the most likely result of the process of the previous question?
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(a) neither are likely; elliptical to spiral or spiral to elliptical (b) mergers (c) elliptical
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What must be measured to determine the distance to a Cepheid variable star?
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The apparent magnitude of the variable star and its period of pulsation
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Which single wavelength band is best for mapping out the spiral arm structure of the Milky Way galaxy?
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Radio
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What fundamental principle did Harlow Shapley use to calibrate the period-luminosity relationship for Cepheid variable stars?
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Objects with large proper motions tend to be closer than objects with small proper motions.
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What measurements are needed to determine the entire mass of the Milky Way galaxy?
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The rotational velocity of a star near the Galaxy's outer edge and the distance to that star.
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What does the observed heavy element abundance tell us about a star?
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A low percentage of metals indicates that a star formed long ago.
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What main conclusion did Harlow Shapley draw from his measurements of the distances to the globular clusters
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The Sun is far from the center of the Milky Way.
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How are population II stars different than the Sun?
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Population II stars have lower metal abundances than the Sun.
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What do we observe at radio, infrared, and X-ray wavelengths near the center of the Milky Way galaxy that leads us to conclude that a supermassive black hole is located there?
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-A strong source of radio waves called Sagittarius A*. -A rapid rate of star formation. -Supernova remnants. -A rapid rate of star formation and supernova remnants.
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Where are the youngest stars in the Milky Way galaxy located?
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In the flattened disk.
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If you could view the Milky Way galaxy from a great distance, what colors would you observe for its different components?
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The disk is blue, the halo is yellow, and the nuclear bulge is yellow.
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Why do astronomers propose that the Milky Way galaxy contains a significant amount of dark matter?
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The Galaxy's rotation curve flattens out at great distances.
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What do astronomers think is responsible for the somewhat flocculent, somewhat grand design spiral arms of the Milky Way galaxy?
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Spiral density waves, self-sustaining star formation, and differential rotation.
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At what wavelength band can we observe the center of our Galaxy?
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Radio, Infrared, and X-ray.
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How are star clusters distributed in the sky?
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Open clusters lie along the Milky Way, and half of the globular clusters are in or near the constellation Sagittarius.
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Which of the following are good visible light spiral-arm tracers?
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O and B associations and H II regions.
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What must we know about an object to use it as a distance indicator?
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Either the object's luminosity or the object's linear size.
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What observable property of a standard candle must be MEASURED to determine its distance?
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Apparent magnitude
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Why is a supernova type Ia standard candle better to use in measuring very long distances than either the brightest globular cluster or Cepheid variable star standard candles?
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Supernovae type Ia are more luminous.
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When viewing a distant galaxy, the amount of look-back time in years is equivalent to the:
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distance to the galaxy divided by the speed of light.
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Which of the following is NOT a distance indicator used in extragalactic astronomy?
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white dwarfs
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Edwin Hubble resolved the Shapley-Curtis debate by measuring the distance to large bright spiral nebulae. What distance method did Hubble employ?
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The Cepheid variable star method.
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How does an Sa galaxy differ from an Sc galaxy?
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The Sa galaxy has less gas and dust.
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What parameter must we know to determine the linear diameter and luminosity of a particular galaxy?
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The distance to the galaxy
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Which feature of a galaxy seems to be related to the mass of the galaxy's central supermassive black hole?
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The mass of the galaxy's central bulge.
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Galaxies with active star formation also have which of the following?
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Plenty of gas and dust, O and B associations, Emission nebulae, & A bluish tint.
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What gives elliptical galaxies a redder color than spiral galaxies?
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Elliptical galaxies have less gas and dust.
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Which of the following is the LEAST important factor in galactic evolution?
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The elemental composition of the material from which galaxies form.
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What was the topic of the Shapley-Curtis Debate of 1920?
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The location of the spiral nebulae.
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How was William Parsons able to see spiral structure in some nebulae in 1845, whereas others had not noticed this spiral structure before?
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His 72 inch diameter telescope was the largest in the world at that time.
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Why are galaxies with active nuclei more often found in close galaxy pairs and in rich clusters of galaxies?
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-Galactic harassment is more likely under these circumstances. -Galactic merger is more likely under these circumstances. -Galactic cannibalism is more likely under these circumstances. -Galactic interactions transfer material onto the central supermassive black holes.
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Seyfert galaxies have a spectrum with broad emission lines of ionized elements. What other unusual features do Seyfert galaxies have?
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They have small, highly luminous nuclei that fluctuate rapidly in brightness.
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Which of the following are characteristics of quasars?
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Quasars have bright emission-line spectra.
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What evidence do we have that quasars are very far away?
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-Their spectral lines have very large redshifts. -Some are gravitationally lensed by distant galaxies -Some of the light from quasars contains lower redshift absorption lines of distant galaxies. -Some quasars have nearby galaxies with similar redshifts in their spectra.
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Galaxies in close pairs are three times more likely to be Seyfert galaxies than are isolated galaxies. What general conclusion can be drawn from this statistical fact?
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Seyfert galaxies are very likely the result of galaxy interactions.
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What observational evidence supports the idea that AGN contain supermassive black holes?
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Broad emission lines of ionized gases indicate that gas near the center of an AGN is orbiting at high velocities, and rapid brightness fluctuations limit the size of the object at the center of an AGN.
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What is the difference between type 1 and type 2 Seyfert galaxies?
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Type 1 Seyferts are more luminous at ultraviolet and X-ray wavelengths than type 2 Seyferts.
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What evidence do we have that quasars are small?
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They show rapid fluctuations in brightness.
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Where are all the dead quasars?
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They lurk quietly at the hearts of galaxies.
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Which of the following characterizes the visible part of the spectrum for most (inactive) galaxies?
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They show stellar absorption lines.
