1	HW12 Solutions Question 1 Seyfert 1 galaxies show very broad emission lines, while Seyfert 2 galaxies show narrower emission lines. What do astronomers think the reason is? a.Seyfert 1 galaxies have bigger black holes than Seyfert 2 galaxies. b.Seyfert 1 galaxies have smaller black holes than Seyfert 2 galaxies. c.Seyfert 1 galaxies have radio jets and Seyfert 2 galaxies don't. d.Seyfert 1 galaxies are actively accreting fuel and tidally disrupting stars, and Seyfert 2 galaxies are not. e.Seyfert 1 galaxies' cores are seen directly, while the centers of Seyfert 2 galaxies are hidden from our perspective by a dense torus of gas and dust. This is the basic point of the unified model of Seyfert galaxies.
2	HW12 Solutions Question 2 (1 point) If the inner accretion disk around a black hole has a temperature of 1 million K, at what wavelength will it radiate the most energy? a.1 million nm b. 3 nm c. 3 million nm d. 1 nm e.10 nm Wien’s Law: λ = 3000000 nm K/T λ = 3 nm (which is in the X-rays) Question 3 (1 point) If we take a spectrum of a quasar and see that the Lyman alpha line, observed in the laboratory at a wavelength of 121.6 nm, appears at a wavelength of 425.6 nm, what is the redshift (z) of this quasar? a. 0.5 b. 1 c. 1.5 d. 2 e. 2.5 z = Δλ/λ and λ = 121.6 nm and Δλ = 425.6 nm – 121.6 nm so z = 304 nm /121.6 nm = 2.5
3	HW12 Solutions Question 4 (1 point) Quasars can be 1000 times more luminous than a galaxy. The absolute magnitude of such a luminous quasar would be about M = -28.5. If the black hole in the center of our galaxy became a quasar, what would the apparent magnitude of the galactic core be? a. -13.9 b.19 c. 0 d.-4.6 e.8.5 We need to use the equation: m – M = -5 + 5 log d(pc) d = 8500 pc, M = -28.5, so: m + 28.5 = -5 + 19.6 m = -13.9
4	HW12 Solutions Question 5 (1 point) The cosmic background radiation comes from a time in the evolution of the universe when a."inflation" was occuring. b. electrons began to recombine with nuclei to form neutral atoms. c. gamma rays had enough energy to destroy nuclei. d. gravity began to pull material together to form galaxies. Question 6 The Hubble constant, which we measure to be about 72 km/s/Mpc, describes the current expansion rate of the local universe. We think the age of the universe is about 14 billion years, in the context of the Big Bang theory. If the Hubble constant were much larger, say 500 km/s/Mpc as Edwin Hubble first reported, then how would our estimate of the age of the universe change? a.It would still be about the same. b.It would be larger, about 7 times larger (500/72), or nearly 100 billion years old. c.It would be much smaller, about 7 times smaller, or about 2 billion years old. Age is inversely proportional to the Hubble constant for essentially all models. Age ~ 1/H. So if the Hubble constant is larger, the time is smaller. Under this assumption, Age = 1/H. Age(H=500)/Age(H=72) = (1/500 km/s/Mpc)/(1/72 km/s/Mpc) Age(H=500)/13.6 Gyrs = 72/500 Age(H=500) = 2 Gyrs As usual, pick the closest answer. We don’t always know numbers like H with high precision.
5	HW 12 Solutions Question 7 What is the area of a circle in a closed universe with spherical geometry? a.The same as in high school Euclidean geometry, π r² b.Smaller than in Euclidean geometry. c.Larger than in Euclidean geometry. Think about drawing circles on a globe along lines of latitude as you move away from the north pole.