A) The star is a halo population star.
B) The star is an extreme Population II star.
C) The star is a disk population star.
D) The star is an intermediate Population II star.
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A) dark halo
B) disk component
C) halo
D) globular clusters
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A) RR Lyrae stars are dimmer and harder to see.
B) RR Lyrae stars pulsate so fast that they can't be measured.
C) RR Lyrae stars are further away than Cepheids.
D) RR Lyrae stars do not have a relationship between period and luminosity.
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A) Orbits of stars indicate a mass several million times that of the Sun within a very small volume.
B) Sagittarius A* is a powerful radio source.
C) No visible light from Sagittarius A* reaches the Earth.
D) Radio maps of the region around Sagittarius A* show complicated gas structures believed to be related to massive star formation.
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A) in the galaxy's globular clusters
B) in the disk of the galaxy
C) in the centre of the galaxy
D) in the galaxy's spiral arms
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A) He measured their proper motions across the sky.
B) He used the period-luminosity relation.
C) He measured their parallax.
D) He measured their spectroscopic parallax.
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A) It has a hot accretion disk that emits a large amount of X-rays.
B) It is launching high-energy jets along its poles.
C) It is destroying stars that get too close to the event horizon.
D) It is mostly dormant with occasional flares.
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A) from a large cloud of material that broke off a larger galaxy
B) from the collapse of a large spherical cloud of gas that was rotating very slowly
C) from material that had been ejected in the violent explosion of a dying galaxy
D) as a result of mergers between several smaller groups of gas, dust, and stars
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A) circular orbits
B) hyperbolic orbits
C) slightly elliptical orbits, all in the same plane
D) highly elongated elliptical orbits
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A) He found the distances to open clusters found throughout the disk of the galaxy.
B) He found the distances to individual variables free-floating in the halo of the galaxy.
C) He determined the proper motion of globular clusters in the outer disk of the galaxy.
D) He found the distances to globular clusters distributed about the centre of the galaxy.
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A) massive compact halo objects
B) neutrinos
C) weakly interacting massive particles
D) supermassive black holes
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A) They reveal that our galaxy is a grand design spiral.
B) They map the location of dense neutral hydrogen clouds.
C) They reveal that the Sun is currently located in the centre of a spiral arm.
D) They map the location of hot O and B stars by the radio radiation they emit.
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A) The rotation of the star sends flashing radio beams of light toward Earth.
B) The opacity of stellar material changes depending on the temperature.
C) The combined light of the Cepheid and an orbiting companion changes as they eclipse each other.
D) The power source alternates between fusing hydrogen and fusing helium.
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