24.5.0 Black Holes

24. What type of main sequence star is most likely to become a black hole? a. an O-type star b. a G-type star c. a K-type star d. an M-type star e. you can't fool me, all spectral types on the main sequence have an equal chance of becoming black holes

a. an O-type star

13. To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at? a. mass b. surface temperature c. color d. distance e. diameter

a. mass

15. Deep inside a black hole (and hidden from our view) is the compressed center, where all the "stuff" of the star goes. Astronomer call this central point a. an event horizon b. a singularity c. a time-stopping point d. a black dwarf e. Bayonne, New Jersey

b. a singularity

14. The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called a. the singularity b. the neutron star radius c. the gravitational redshift zone d. the event horizon e. day-time television

d. the event horizon

19. Which of the following can a black hole not "eat" (swallow)? a. a planet b. a cloud of gas and dust c. a star d. another black hole e. you can't fool me, black holes can eat anything

e. you can't fool me, black holes can eat anything

17. The astronomer who first worked out the mathematical description of black hole event horizons was a. Edwin Hubble b. Jocelyn Bell c. Karl Schwarzschild d. S. Chandrasekhar e. Frederik Pohl

c. Karl Schwarzschild

16. In the far future, a starship becomes trapped inside the event horizon of a black hole. Although the crew discovers that their ship cannot out, they at least want to send a message to other ships in the area to stay away from the danger zone. If they send out a message in the form of a radio wave, what will be its fate? a. the message will emerge from the event horizon with a huge gravitational redshift b. although the radio wave will emerge from the event horizon, all the information in the message will be garbled c. the radio wave will become a gamma ray by the time it emerges from the event horizon d. the radio wave will only emerge from the event horizon if it is moving in the direction of the magnetic north and south pole of the star that formed the black hole e. the message will never emerge from the event horizon

e. the message will never emerge from the event horizon

21. Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, your watch near the black hole will run: a. more slowly b. more quickly c. infinitely slow d. infinitely fast e. you can't fool me, watches near a black hole don't change the pace at which they run

a. more slowly

18. Once a black hole forms, the size of its event horizon is determined only by a. the size (diameter) of the star that collapsed into the black hole b. the mass inside the event horizon c. the time since the black hole formed d. the composition of the material that formed the black hole e. you can't fool me; every black hole has an event horizon of the same size

b. the mass inside the event horizon

23. A handsome, rich, but vain movie star notices that he is starting to age, and consults you as his astronomy expert, to see if you can find an astronomical way to slow down his aging. Putting aside practical considerations (such as the fact that we cannot travel to other stars), which of the following strategies would IN THEORY allow him to age more slowly than the rest of humanity. a. he should always live at sea level on Earth, and never go to any mountains or high altitudes b. he should live far away from the gravity of any planet or star (in a deep-space station) c. he should be in orbit around the Earth, and expose himself to as many cosmic rays as possible d. he should travel to a black hole, and spend some time in orbit just above the event horizon e. he should live in a room filled with positive electrical charge

d. he should travel to a black hole, and spend some time in orbit just above the event horizon

22. When scientists say that "black holes have no hair", what do they mean? a. that the event horizon of a black hole is very smooth and does not have parts that jut out b. that if you threw something toward a black hole (a rabbit, say) it would quickly be ripped apart into smaller pieces c. that time near a black hole slows down so much our hair would not grow at a normal rate d. that once a black hole forms, very little information can be extracted from it about the material that is now inside e. no one knows what this means; regular people are not meant to figure out some of the weird things physicists say about black holes

d. that once a black hole forms, very little information can be extracted from it about the material that is now inside

20. Suppose each of the following objects could collapse into a black hole. Each black hole would have a sphere around it that is the limit for escape -- once you are inside this region, you cannot get away. For which object would this region be the largest in diameter? a. a star with the mass of our Sun b. a planet like Jupiter c. a star that was type O when it was on the main sequence d. an entire cluster of stars (with about 150 stars in it) e. an entire galaxy of stars (with about a billion stars in it)

e. an entire galaxy of stars (with about a billion stars in it)