1 Astronomy HOMEWORK QUESTIONS Chapter 14 Which property, if any, of normal matter ceases to exist in a bla ck hole? a. mass, b. chemical 1. composition, c. angular momentum, d. electric charge, e. all of these properties exist in a black hole. nitely exist. b. Chemical composition, although this is debated. a,c,d defi 2. Supermassive black holes are found in which of the following lo cations? a. in the centers of galaxies, b. in globular clusters, c. in open (or galactic) clust ers, d. between galaxies, e. in orbit with a single star. a. centers of galaxies. “Supermassive” is the key term. 3. Which feature is found with Kerr black holes but not Schwarzsc hild black holes? a. a f photons outside of the black hole, singularity, b. an event horizon, c. gravitational redshift o d. an ergoregion, e. warping of nearby spacetime d. ergoregion. If the Sun suddenly became a black hole, how would Earth’s orbi 6. t be affected? Earth’s orbit would not be affected. A black hole only has its g ravity, which would be exactly the same as the Sun’s. The loss of the Sun’s heat and light would make D arkEarth uninhabitable, though. 9. tes members of close binary Why are all of the observed stellar-remnant blackhole candida systems? Because it’s the presence of the companion that makes them dete ctable: material from the companion going into an accretion disk around the BH gets extr emely hot, and/or the presence of a companion allows determination of the mass. 10. If light cannot escape from a black hole, how can we detect X-ray s from such an object? hat heats the accretion disk so It’s the material OUTSIDE the event horizon spiraling inward t hot it emits X-rays. What is the Schwarzschild radius of a black hole, measured in ki lometers, containing 3 M 11. ? ⊙ 30 M ? ⊙ Use the simple formula in Astronomers Toolbox 14-1, page 449: R ): so, 9 km and 90 km. = (3 km)( M BH Sch 15. You are standing in a train car at rest in the station, as in Figure 14-2. You measure the car’s length to be 10 m long. The train speeds up to the considera ble speed of 0 . 95 c with you still inside the car. How long will you measure the car to be now? Ex plain how you got your answer. 10 m. The car is STATIONARY relative to you, so you measure its leng th the same. The person on the platform, who is moving at 0 . 95 c relative to you, measures the train to be shorter.