Reference no: EM133296837

Question

1. Astronomers believe there are supermassive black holes at the centers of galaxies because

a. galactic centers of nearby galaxies are a strong source of gravitational waves, indicating high masses there.

b. stellar motion there indicates there is more mass than can be accounted for with normal matter.

c. distant background quasars are gravitationally lensed by these central black holes.

d. observations show gas clouds disappearing as they cross the event horizon of the enormous black hole.

2. Stars in the outer parts of the Milky Way

a. are moving more quickly than they should be if the majority of the Galaxy's mass is luminuous material.

b. are younger than expected if spiral galaxies form by mergers of dwarf spheroidals.

c. should be brighter than they are observed to be if current stellar evolution theories are correct.

d. have a much higher metallicity than expected based on the Galaxy's age.