1. One object that is believed to be a black hole in our Galaxyis
A the central star inthe planetary nebula, the Ring Nebula in Lyra.
B the central star in theCrab Nebula.
C Cygnus X-1, a powerfulx-ray source.
D the Vela pulsar.

2. X-rays that come from the vicinity of a black hole actually originate
A from well inside theevent horizon.
B from just outside theevent horizon, on the accretion disk.
C from its exact center, orsingularity.
D from relatively far awayfrom the black hole, where matter is quite cool.

3. In a binary star system, an unseen component is found to have amass of about 8 solar masses. It would be visible if this were anormal star, so it must be a collapsed object. Theoreticalconsiderations tell us that it must be
A a browndwarf.
B a neutron star.
C a black hole.
D a white dwarf.

4. Where would you look for a supermassive black hole?
A At the center of asupernova remnant.
B Orbiting a normal star inour galaxy.
C In the center of agalaxy.
D At the center of theuniverse.

5. What is the Schwarzschild radius of a black hole?
A The radius of thesingularity.
B The distance from thesingularity to the point at which the X-rays that we see from theEarth are emitted.
C The distance from thesingularity to the point where nothing can escape from the blackhole.
D The distance from thesingularity to the point where any object entering will gain energybefore leaving again.

6. What is the event horizon of a black hole?
A The "surface" atwhich all events happen.
B The infinitesimally smallvolume at the center of the black hole that contains all of theblack hole's mass.
C The "surface" from insideof which nothing can escape.
D The "surface" insidewhich any object entering will leave with a greater energy thanthat with which it entered.

7. If nothing can ever leave a black hole, can the mass of a blackhole ever decrease?
A Yes, ifparticle-antiparticle pairs are created outside the event horizonand one particle enters the event horizon while the otherescapes.
B Yes, if the matter insidethe black hole is radioactive (e.g., uranium), then alphaparticles, electrons and gamma rays are constantly leaving theblack hole.
C Yes, if antiparticlesenter a black hole and annihilate with matter already inside theblack hole.
D No.