Multiple choice: The presence of a black hole in a galaxy corecan be inferred from (a) the total mass of the galaxy; (b) thespeeds of stars near the core; (c) the color of the galaxy; (d) thedistance of the galaxy from the Milky Way Galaxy; or (e) thediminished brightness of starlight in the galaxy core, relative tosurrounding areas.

Multiple choice: Which one of the following statements aboutblack holes is false? (a) Inside a black hole, matter is thought toconsist primarily of iron, the endpoint of nuclear fusion inmassive stars. (b) Photons escaping from the vicinity of (but notinside) a black hole lose energy, yet still, travel at the speed oflight. (c) Near the event horizon of a small black hole (mass = afew solar masses), tidal forces stretch objects apart. (d) A blackhole that has reached an equilibrium configuration can be describedentirely by its mass, electric charge, and amount of spin (“angularmomentum”). (e) A black hole has an “event horizon” from which nolight can escape, according to classical (i.e., non-quantum)ideas.

Multiple choice: Which one of the following statements aboutblack holes is true? (a) The surface of the singularity of a blackhole is known as the event horizon. (b) Being more massive, asupermassive black hole has a greater gravitational pull than astellar-mass black hole, so if you approach the event horizon of asupermassive black hole, you will be torn apart more easily than ifyou approach the event horizon of a stellar-mass black hole. (c) Ifthe Sun were to become a black hole of the same mass, Earth wouldspiral into the black hole and be eaten. (d) The “photon sphere” isa region inside a black hole where photons orbit the center, sothey cannot escape. (e) In principle, energy can be extracted froma region outside a rotating black hole.

Multiple choice: Which one of the following statements about thedetection (or potential detection) of black holes is false? (a)Black holes cannot be detected because they emit no light and aretherefore impossible to directly observe. (b) A binary pair ofblack holes was recently detected through measurements of thegravitational waves emitted when they merged to form a single blackhole. (c) The presence of supermassive black holes in the centersof galaxies has been inferred from the motions of stars and gasnear them. (d) Evidence for black holes can be found if material inthe surrounding accretion disk goes through the event horizon andfades from view, rather than releasing energy as it hits a hardstellar surface. (e) Candidate black holes are sometimes found inbinary systems that suddenly brighten at X-ray wavelengths.