Question

Multiple choice: The presence of a black hole in a galaxy core can be inferred from (a) the total mass of the galaxy; (b) the speeds of stars near the core; (c) the color of the galaxy; (d) the distance of the galaxy from the Milky Way Galaxy; or (e) the diminished brightness of starlight in the galaxy core, relative to surrounding areas.

Multiple choice: Which one of the following statements about black holes is false? (a) Inside a black hole, matter is thought to consist primarily of iron, the endpoint of nuclear fusion in massive stars. (b) Photons escaping from the vicinity of (but not inside) a black hole lose energy, yet still, travel at the speed of light. (c) Near the event horizon of a small black hole (mass = a few solar masses), tidal forces stretch objects apart. (d) A black hole that has reached an equilibrium configuration can be described entirely by its mass, electric charge, and amount of spin (“angular momentum”). (e) A black hole has an “event horizon” from which no light can escape, according to classical (i.e., non-quantum) ideas.

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

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

Answer 1

1) The presence of a black hole in a galaxy core can be inferred from the speeds of stars near the core (B)....

2) following statements about black holes is false--Inside a black hole, matter is thought to consist primarily of iron, the endpoint of nuclear fusion in massive stars. (A)

3) following statements about black holes is true---Being more massive, a supermassive black hole has a greater gravitational pull than a stellar-mass black hole, so if you approach the event horizon of a supermassive black hole, you will be torn apart more easily than if you approach the event horizon of a stellar-mass black hole. (B)

In principle, energy can be extracted from a region outside a rotating black hole.(E)

4) following statements about the detection (or potential detection) of black holes is false ---Evidence for black holes can be found if material in the surrounding accretion disk goes through the event horizon and fades from view, rather than releasing energy as it hits a hard stellar surface (D)