Astronomy 89 Homework 11
Which of these is inferred to be a black hole? 1. Cygnus X-1 2. the Crab nebula 3. the Pleiades 4. the Orion Nebula
1. Cygnus X-1
What explanation does general relativity provide for gravity? 1. Gravity is the result of curved spacetime. 2. Gravity is directly proportional to the mass of the attracting body. 3. Gravity can only affect particles that have mass, not light. 4. Gravity is the opposite of the electromagnetic force.
1. Gravity is the result of curved spacetime.
Deep inside a black hole (and hidden from our view) is the compressed center, where all the "stuff" of the star goes. Astronomers call this central point 1. a singularity 2. the event horizon 3. a black dwarf 4. the accretion disk
1. a singularity
When Einstein proposed his General Theory of Relativity, he suggested some pretty strange ideas about space, time, and gravity. How did scientists in 1919 show that Einstein's theory described the behavior of the real world and wasn't just a crazy hypothesis? 1. by observing starlight coming close to the Sun during an eclipse 2. by finding x-rays from a black hole 3. by using an H-R diagram for a nearby cluster of stars 4. by discovering the process of nuclear fusion
1. by observing starlight coming close to the Sun during an eclipse
According to the general theory of relativity, the presence of mass: 1. causes a curvature (or warping) of spacetime 2. is equivalent to the presence of light 3. causes curved paths to straighten out until they are exactly straight lines 4. causes motion at the speed of light squared
1. causes a curvature (or warping) of spacetime
When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays usually coming from? 1. from a disk of material around the black hole (material that has been 2. pulled from the companion star and is falling toward the black hole) from inside the black hole event horizon 3. from the photosphere of the companion star (the star that is not a black hole) 4. from the singularity
1. from a disk of material around the black hole (material that has been 2. pulled from the companion star and is falling toward the black hole)
To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at? 1. mass 2. surface temperature 3. luminosity 4. distance
1. mass
How would you describe the size of the Schwarzschild radius of a supermassive black hole of 20 million solar masses? Note that 1 AU = 150 million km 1. smaller than the orbit of the Earth around the Sun 2. approximately the size of the Solar System 3. as large as the distance of the Sun from the nearest star 4. approximately the size of the Earth
1. smaller than the orbit of the Earth around the Sun
The term "event horizon" refers to 1. the distance from the center of a black hole at which the escape velocity becomes equal to the speed of light. 2. the distance to which gas is ejected in a planetary nebula. 3. half the diameter of a neutron star. 4. half the diameter of the singularity in a black hole
1. the distance from the center of a black hole at which the escape
Once a black hole forms, the size of its event horizon is determined only by 1. the mass inside the event horizon 2. the size (diameter) of the star that collapsed into the black hole 3. the composition of the material that formed the black hole 4. how much mass was ejected in the supernova explosion that formed the black hole
1. the mass inside the event horizon
