exam 3 (1)

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University of Texas, Rio Grande Valley *

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3354

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Astronomy

Date

Apr 3, 2024

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docx

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 What kind of objects lie in the disk of our galaxy? All of the above  A lenticular galaxy is another name for an elongated elliptical galaxy. False  What is Hubble’s law? The recession velocity of a galaxy is inversely proportional to its distance  Most of the current star formation in the Milky Way occurs in its spiral arms. True  Why are Cepheid variables important? Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true luminosities.  All spiral galaxies have both a disk and spheroidal component to their stellar populations. True  Where does most star formation occur in the Milky Way Galaxy? In the spiral arms  How does a lenticular galaxy differ from a normal spiral galaxy? It has no spiral arms  All elements heavier than iron are made during supernova explosions. True  Based on counting the number of galaxies in a small patch of the sky and multiplying the number of galaxies in the observable universe is estimated to be approximately. 100 billion  Why has star formation ceased in the galactic halo? All of the galaxy’s cool gas settled to the galactic plane long ago.  The most common form of gas in the disk of the Milky Way galaxy is. Atomic Hydrogen Gas  What is the diameter of the disk of the Milky Way? 100,000 light years  Which types of galaxies have a clearly defined spheroidal component? All but irregulars  How did Edwin Hubble measure the distance to the Andromeda Galaxy? He applied the period luminosity relation to Cepheid variables in Andromeda  Hubble's galaxy classification diagram (the "tuning fork") ________. Relates galaxies according to their shapes, but not according to any evolutionary status  What is the best evidence for an extremely massive black hole in the center of the Milky Way? The orbits of stars in the center of the galaxy indicate that the presence of 3 to 4 million solar mass object in a region no larger than our Solar System  How does the interstellar medium obscure our view of most of the galaxy? The small mixture of dust grains in the interstellar medium absorbs visible light.  A protogalactic cloud with very little angular momentum is more likely to form an elliptical galaxy than a spiral galaxy. True  Spiral arms appear bright because... they contain more hot young stars than other parts of the disk  What is a quasar? The extremely bright center of a distant galaxy thought to be powered by a supermassive black hole.  Which of the following is not one of the three major categories of galaxies? globular galaxies  Based on current estimates of the value of Hubble’s constant, how old is the universe? 12 to 15 billion years old  Why do we believe that most of the mass of the Milky Way is in the form of dark matter? 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  We can study how galaxies evolve because... the farther away we look, the further back in time we see  What is the main sequence fitting? A method for determining the distance to a star cluster by assuming that its main sequence should line up with the main sequence on a standard H-R diagram

 Distant galaxies are more likely to be irregular in shape than galaxies closer to the Milky Way. True  Over time, the star-gas-star cycle leads the gas in the Milky Way to... have a greater abundance of heavy elements  What is the most accurate way to determine the distance to a nearby star? Stellar parallax  What is a standard candle? an object for which we are likely to know it's true luminosity  All of the following types of objects are found almost exclusively in the disk (rather than the halo) of the Milky Way except... globular clusters  Although the entire universe may be much larger than our observable universe, we can see only written out observable universe. The “boundary” of our observable universe is called... the cosmological horizon  Which types of galaxies have a clearly defined disk component? Spirals and lenticulars  How do observations of galaxies at different distances help us learn about galaxy evolution? Observations of different distances show galaxies of different ages and therefore different stages of evolution.  What is the thickness of the disk of the Milky Way? 1,000 light years  Which of the following types of galaxies have a disk and spheroidal component but lack spiral arms? Lenticulars  The galactic center lies in the direction of which constellation? Sagittarius  What is the most accurate way to determine the distance to a nearby galaxy? Cepheid variables  The unusually bright center found in some galaxies are called... a ctive galactic nuclei  Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy? A dense cloud with very little angular momentum  Approximately how far is the Sun from the center of the galaxy? 27,000 light years  How do disk stars orbit the center of the galaxy? They all orbit in roughly the same plane and in the same direction.  Why should galaxy collisions have been more common in the past than they are today? Galaxies were closer together in the past because the universe was smaller.  Galaxy collusions were more common in the past. True  What does Hubble’s law tell us? The most distant a galaxy, the faster it is moving away from us  The Sun’s location in the Milky Way Galaxy is.. In the galactic disk, roughly halfway between the center and the outer edge of the disk  If we say that a galaxy has a lookback time of 1 billion years, we mean that.. Its light traveled through space for 1 billion years to reach us  Stars continue to form in the halo of our Galaxy today. False

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