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Question 1

The star Regulus, in the constellation Leo, appears brighter through a blue filter than it does through a yellow filter. Suppose that a second star is found that has the same brightness as Regulus through the blue filter but is brighter than Regulus through the yellow filter. From this information, we can say conclusively that the second star has   

· 1.

· a higher temperature.

· 2.

· a lower temperature.

· 3.

· the same temperature but a higher luminosity.

· 4.

· the same temperature but a lower luminosity.

1 points

Question 2

·   Light leaving a point source spreads out so that the apparent brightness I of light per unit area varies with distance d according to which of the following laws (∝ means “proportional to”)?   

· 1.

· 2.

· 3.

· 4.

· I ∝ 1/d

· I = constant

· I ∝ d2

· I ∝ 1/d

·  
1 points

Question 3

·   Which of the following observations would NOT be an indication of a binary star system?   

· 1.

· 2.

· 3.

· 4.

· A “star” image periodically separates into two distinct images and then blends again.

· The “star” appears to move in a straight line against a background field of stars.

· A “star” appears to become periodically dimmer and then brighter for a few hours at a time.

· The “star” appears to wiggle in its path across Earth’s sky against the background stars.

·  
1 points

Question 4

·   The relative brightness of a star as we see it in Earth’s sky is called   

· 1.

· 2.

· 3.

· 4.

· surface temperature.

· absolute magnitude.

· luminosity.

· apparent magnitude.

·  
1 points

Question 5

·   How bright (in absolute magnitude) are the intrinsically faintest stars in the universe?   

· 1.

· 2.

· 3.

· 4.

· +1

· 0

· –10

· +1

·  
1 points

Question 6

·   What is spectroscopic parallax?   

· 1.

· 2.

· 3.

· 4.

· apparent change in position of a nearby star compared with distant background

· stars due to the motion of Earth around the Sun

· change in position of the absorption lines in a star’s spectrum due to the Doppler

· shift caused by the star’s motion around the center of mass in a binary star system

· distance to a star measured using the spectral luminosity class of the star and the

· inverse square law

· apparent change in position of the absorption lines in a star’s spectrum due to the

· Doppler shift caused by Earth’s motion around the Sun

·  
1 points

Question 7

·   Two stars whose apparent magnitudes differ from each other by five magnitudes have a ratio of brightnesses of   

· 1.

· 2.

· 3.

· 4.

· 10.

· 25.

· 2.5.

· 100.

·  
1 points

Question 8

·   A white dwarf star whose temperature is the same as that of the Sun will have a radius that is (see Fig. 11-8, Comins and Kaufmann, Discovering the Universe, 8th Ed.)   

· 1.

· 2.

· 3.

· 4.

· the same size as the Sun’s.

· 100 times smaller than that of the Sun.

· 10 times smaller than that of the Sun.

· 2 times smaller than that of the Sun.

·  
1 points

Question 9

·   Stellar parallax appears because   

· 1.

· 2.

· 3.

· 4.

· Earth rotates about its own axis.

· stars have finite size (i.e., they are not really just points of light).

· stars move in space.

· Earth moves in space.

·  
1 points

Question 10

·   We are about 8000 parsecs from the center of the Milky Way Galaxy, and the smallest parallax angle we can measure from orbiting observatories is about 0.001 arcseconds. How far toward the galactic center can we see with this technique (ignoring galactic dust and other obstacles)?   

· 1.

· 2.

· 3.

· 4.

· only 0.008 = 1/125 of the way to the center

· about 1/8 of the way to the center

· all the way to the center

· about halfway to the center

Question 11

·   Which statement best describes the “fabric” of space and time as outlined by the classical physics of Newton?   

· 1.

· 2.

· 3.

· 4.

· Space is expanding uniformly, while time passes more slowly as the universe ages.

· Space is perfectly uniform, filling everywhere like a fixed network, while time passes

· at a uniform rate for all observers.

· Space becomes “curved” and time slows down near a source of gravity, as measured

· by a distant observer.

· The shape of space and the rate of passage of time depend on the relative velocities

· of observer and observed.

1 points

Question 12

·   In the context of black holes, the word ergosphere names the   

· 1.

· 2.

· 3.

· 4.

· entire region inside the event horizon.

· region just outside the event horizon of a rotating black hole where it is impossible

· for anything to remain at rest.

· region occupied by the accretion disk where matter from a companion star collects

· around a black hole.

· entire universe outside the black hole.

·  
1 points

Question 13

·   What method is used by astronomers to infer the existence in space of a dark object of about 5 solar masses, such as a black hole?   

· 1.

· 2.

· 3.

· 4.

· estimation of the luminosity of the object and the application of the

· mass-luminosity relationship

· measurement of the effect of its gravitational force on a companion

· object in a binary system

· infrared imaging of a region whose effective temperature is lower than

· the cosmic microwave background, rendering it dark

· measurement of the gravitational redshift of spectral lines in the spectrum

· of the object

·  
1 points

Question 14

·   A black hole is so named because   

· 1.

· 2.

· 3.

· 4.

· the gravitational field is so high that the wavelength of its emitted light

· is gravitationally redshifted to radio wavelengths.

· no light can escape from it due to its powerful gravitational field.

· it emits no visible light because it is so cold, less than 100 K.

· it is colder that the rest of the universe; that is, its effective temperature is less than 3 K.

·  
1 points

Question 15

·   What is the typical duration of a gamma-ray burst?   

· 1.

· 2.

· 3.

· 4.

· less than a couple of minutes, indicating a source smaller than Mercury’s orbit

· several hours, indicating a source somewhat larger than the solar system

· several days, indicating a size much smaller than the distance from Earth

· to the nearest star beyond the Sun

· up to about 1 hour, indicating a source less than half the size of the solar system

·  
1 points

Question 16

·   In the context of black holes, a singularity is a(n)   

· 1.

· 2.

· 3.

· 4.

· place just outside the event horizon of a rotating black hole where it is

· impossible to remain at rest.

· place where the escape velocity exactly equals the speed of light.

· entry point in the event horizon of a black hole through which material

· is allowed to pass unhindered.

· place where a nonzero mass occupies zero volume.

·  
1 points

Question 17

·   Sometimes particle-antiparticle pairs are created and then annihilate so quickly that we cannot know that they ever existed. What are these particles (or antiparticles) called?   

· 1.

· 2.

· 3.

· 4.

· temporary particles

· relativistic particles

· virtual particles

· field particles

·  
1 points

Question 18

·   How do Kerr black holes differ from Schwarzschild black holes?   

· 1.

· 2.

· 3.

· 4.

· Kerr black holes rotate; Schwarzschild black holes do not.

· Kerr black holes have infinite mass; Schwarzschild black holes do not.

· Kerr black holes have accretion disks; Schwarzschild black holes do not.

· Kerr black holes have net electric charge; Schwarzschild black holes do not.

·  
1 points

Question 19

·   The Schwarzschild radius is   

· 1.

· 2.

· 3.

· 4.

· the distance to which gas is ejected in a planetary nebula.

· half the diameter of the singularity in a black hole.

· half the diameter of a neutron star.

· the distance from the center of a black hole to the point at which the

· escape velocity becomes equal to the speed of light.

·  
1 points

Question 20

·   What is Hawking radiation?   

· 1.

· 2.

· 3.

· 4.

· stream of particles and antiparticles from just outside the event horizon

· of a black hole

· microwaves from the edge of the visible universe

· electromagnetic radiation from electrons spiraling in the magnetosphere

· of a neutron star

· X rays from an accretion disk around a black hole

Question 21

·   One of the first three astronomical objects detected at radio wavelengths by Grote Reber in the late 1930s was   

· 1.

· 2.

· 3.

· 4.

· the Moon.

· the Sun.

· the galactic center.

· Jupiter.

·  
1 points

Question 22

·   BL Lacertae objects appear to be   

· 1.

· 2.

· 3.

· 4.

· spiral galaxies with bright, starlike nuclei.

· elliptical galaxies with bright, starlike nuclei.

· active galaxies, most of whose energy is emitted by two widely spaced radio lobes.

· giant irregular galaxies with neither spiral arms nor the smooth shape of elliptical galaxies.

·  
1 points

Question 23

·   The fact that quasars can be detected from distances from which even the biggest and most luminous galaxies cannot be seen means that   

· 1.

· 2.

· 3.

· 4.

· they must be far more luminous than the brightest galaxies.

· they must be in directions where intergalactic absorption by dark matter is

· minimum, allowing us to see them.

· their spectra have not been as redshifted by their motion as those of galaxies

· and hence they can still be seen.

· they must be in directions where gravitational focusing by the masses of nearer

· galaxies makes them visible from Earth.

·  
1 points

Question 24

·   Quasars appear to be   

· 1.

· 2.

· 3.

· 4.

· very distant and intrinsically bright objects moving in random directions at high speeds.

· very distant, intrinsically faint objects with very high blueshifts in their spectra.

· very distant, intrinsically bright objects with very high redshifts

· relatively close with very high redshifts.

·  
1 points

Question 25

·   Which one of the following properties do Seyfert galaxies and the Milky Way Galaxy share?   

· 1.

· 2.

· 3.

· 4.

· spectrum containing strong emission lines from elements such as highly ionized iron

· significantly varying energy output over a few weeks

· spiral galaxy classification

· bright starlike nucleus

·  
1 points

Question 26

·   Seyfert galaxies are   

· 1.

· 2.

· 3.

· 4.

· elliptical galaxies with extremely bright nuclei.

· spiral galaxies with extremely active cores.

· supergiant elliptical galaxies that are periodically disturbed by supernova

· explosions within them.

· active galaxies that shine mainly by radiation from two relatively widely

· spaced radio lobes.

·  
1 points

Question 27

·   Quasars all appear to be   

· 1.

· 2.

· 3.

· 4.

· moving across our line of sight at very high speeds, as seen in time-lapse photographs.

· moving away from us at very high speeds, up to about 90% of the speed of light.

· moving toward us at high speeds, as high as 90% of the speed of light.

· extremely massive objects in the Milky Way Galaxy, their spectra showing very

· high gravitational redshift.

·  
1 points

Question 28

·   Seyfert galaxies are   

· 1.

· 2.

· 3.

· 4.

· irregular galaxies with no shape or structure.

· very small elliptical galaxies.

· active galaxies with bright, starlike nuclei.

· the largest galaxies in the universe.

·  
1 points

Question 29

·   The distance to the bright quasar 3C 273 is estimated to be   

· 1.

· 2.

· 3.

· 4.

· just beyond the Milky Way.

· 3 million ly.

· 2 billion ly.

· 20,000 ly.

·  
1 points

Question 30

·   What is an Einstein ring?   

· 1.

· arc of relativistic particles ejected from a galactic nucleus

· 2.

· ring of material in some spiral galaxies created by a collision with a smaller galaxy

· 3.

· accretion disk around a black hole

· 4.

· example of the image formed by a gravitational lens

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