HSU Astronomy chapter 13 – Flashcards
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A particular galaxy has a nuclear region of more or less uniform brightness from which long lanes of stars curve outward. What type of galaxy is this?
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Spiral
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An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a large nuclear region and tightly wound arms. How should the astronomer classify these galaxies?
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Sa
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Astronomy with a radio telescope was initiated by
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an amateur astronomer Grote Reber, after Jansky had detected radio energy from the galaxy.
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Double radio sources, quasars, and BL Lacertae objects are now considered to be the same basic type of object—an accretion disk producing two oppositely directed jets—but appear to us to be very different because
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we view them at different angles to the line of the double jets. Face-on to the accretion disk the source will look like a BL Lac object, edge-on as double radio sources, and between these positions a quasar
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Faint star like objects producing intense radio energy that eventually were called quasars were found to have an unusual feature in their optical spectra. This feature was
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an extreme redshift of emission lines that indicated high recessional velocities and hence great distances, requiring extremely high energy output in order to be detected
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In the "unified model" of active galaxies, the main difference between quasars, BL Lacertae objects, and radio galaxies appears to be that
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we see the accretion disk around the central black hole from a different angle in each case—face-on for BL Lacertae, edge-on for radio galaxies, and in between for quasars
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In the verification of the Hubble law for the expansion of the universe and the determination of the constant H0, the greatest difficulty has been
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the accurate determination of distances to very distant galaxies.
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One of the first three astronomical objects detected at radio wavelengths by Grote Reber in the late 1930s was
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the galactic center
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Quasars appear to be
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very distant and intrinsically bright objects moving in random directions at high speeds.
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Seyfert galaxies are
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spiral galaxies with extremely active cores
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The Hubble law, representing observations of distant objects in the universe, relates which two parameters?
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The mass of a distant object and its recession velocity.
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The Milky Way Galaxy appears to have a spiral structure with
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four separate major arms
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The distance to the bright quasar, 3C 273, is estimated to be
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2 billion light years
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The factor that misled Herschel into concluding that the stars of the Milky Way were distributed with the Sun at the center of the Galaxy was
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interstellar dust, which obscured the more distant stars and thereby localized his observations.
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What is a barred spiral galaxy?
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A galaxy with a bar through the nuclear bulge and the spiral arms starting from the ends of the bar
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What is an Einstein ring?
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An example of the image formed by a gravitational lens
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What is the Hubble classification for a spiral galaxy with a small nuclear region and loosely wound arms?
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Sc
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What is the Local Group?
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A cluster of about 30 galaxies of which the Milky Way is a member.
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What is the galactic halo?
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A spherical distribution of stars and globular clusters centered on the nuclear bulge.
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What is the most outstanding feature of a quasar compared to other objects in deep space?
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Its enormous output of energy.
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What method is used to determine the distances of very remote galaxies?
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Use of their spectral redshifts and the Hubble law.
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What name is given to a galaxy with a smooth distribution of brightness and a round shape?
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E0
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What name is given to a galaxy with a smooth distribution of brightness and a very elongated shape?
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E7
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Where is the Sun located in our galaxy?
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In or close to the Orion arm, which is between the Sagittarius and Perseus arms.
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Who developed the classification system that divides galaxies into spiral, elliptical, and irregular and classifies spirals by the size of their nuclear region and the tightness of winding of their arms?
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Edwin Hubble.
