CHAPTER 16: CONCEPT QUIZ – Flashcards
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In a photo like the Hubble Deep Field, we see galaxies in many different stages of their lives. In general, which galaxies are seen in the earliest (youngest) stages of their lives?
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the galaxies that are farthest away
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The most basic difference between elliptical galaxies and spiral galaxies is that...
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elliptical galaxies lack anything resembling the disk of a spiral galaxy
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Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?
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we can learn the distance to the galaxy
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In 1924, Edwin Hubble proved that the Andromeda Galaxy lay far beyond the bounds of the Milky Way, thus putting to rest the idea that it might have been a cloud within our galaxy. How was he able to prove this?
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by observing individual Cepheid variable stars in Andromeda and applying the period-luminosity relation
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Assume that Hubble's constant is 22 km per second per million light-years. How fast would we expect a galaxy 100 million light-years away to be moving? (Assume motion is due only to Hubble's law)
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away from us at 2,200 km/s
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Why are white dwarf supernovae more useful than massive star supernovae for measuring cosmic distances?
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white dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak luminosities
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Does Hubble's law work well for galaxies in the Local Group? Why/why not?
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no, because galaxies in the Local Group are gravitationally bound together
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What is the best way to determine a galaxy's redshift?
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take a spectrum of the galaxy, & measure the difference in wavelength of spectral lines from the wavelengths of those same lines as measure in the laboratory
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What statement correctly describes the relationship between expansion rate & age for the universe?
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the faster the rate of expansion, the younger the age of the universe
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What does cosmological redshift do to light?
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stretches its wavelength
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Why can't we see past the cosmological horizon?
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beyond the cosmological horizon, we would be looking back to a time before the universe was born
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We can study how galaxies evolve because...
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we are really smart astronomers, and the farther away we look, the further back in time we see
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What statement is NOT an assumption used in models of galaxy formation?
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gas contracted to form the disks of galaxies before any stars were born
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1 possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interaction, we'd expect this galaxy to be...
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a spiral galaxy
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What phenomena is NOT thought to be a result of collisions or other interactions between galaxies?
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the fact that spiral galaxies have both disk & halo components
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Interactions among galaxies also are thought to influence a galaxy's type in at least some cases. What does NOT support the idea that interactions can shape galaxies?
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the fact that more distant galaxies have larger redshifts
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What characteristic is NOT generally true of a starburst galaxy?
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the observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center
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Observations indicated that over billions of years, galaxies in general tend to change from...
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smaller & bluer to larger & redder
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A quasar's spectrum is hugely redshifted. What does this large redshift tell us about the quasar?
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the distance to the quasar
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Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?
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active galactic nuclei tend to become less active as they age
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Suppose we observe a source of X-rays that varies substantially in brightness over a period of a few days. What can we conclude?
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the X-ray source is no more than a few light-days in diameter
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Which observation does NOT support the model in which active galactic nuclei are powered by accretion disks around massive black holes?
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the most luminous active galactic nuclei have huge redshifts
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According to the model in which active galactic nuclei are powered by supermassive black holes, the energy released as light comes from...
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gravitation potential energy released by matter that is falling toward the black hole
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The observed relationship between the masses of central black holes & the bulge masses of galaxies implies that...
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galaxy formation & supermassive black hole formation must be related somehow
