PHY197F

Essay 2: Black Holes (10%)

Due dates

Where to submit

Topic

Tell me about black holes. Be sure to answer the following ten sub-questions along the way; each is worth about the same marks. The choice of which order you answer them in is up to you.

  1. Explain the concept of escape speed from a gravitating body. How big is it for Earth? Why did NASA pick Cape Canaveral as a rocket launch base?
  2. How do physicists define a black hole? Explain the black part of the name.
  3. What are the key physical characteristics of a black hole? (You may include a sketch if you like.)
  4. Is more than one kind of black hole possible? Explain.
  5. Describe what happens to a pebble feeling the gravity of a black hole. Must it eventually fall in, or could it orbit? How about a planet?
  6. In Einstein's theory of gravity (unlike in Newton's), photons can orbit a black hole. How can this happen? What would we see from outside?
  7. How do black holes arise astrophysically, in our universe?
  8. What techniques do astronomers use to figure out whether a compact astrophysical object is a black hole or not?
  9. What are some limitations on our ability to learn about black holes?
  10. What would an astronaut feel if she tried to poke her finger through a black hole horizon?

Format, style, intended readership, etc. should be the same as for your first essay. You may assume that the audience for this essay has read your previous one. Please focus your effort on providing clear, understandable, accurate explanations of the physics concepts. Don't forget to include your completed signed academic integrity checklist.

Useful Resources

In addition to my lecture notes, you are also expected to find some sources by yourself. University teachers prefer sources to be articles, books, or websites written by people or groups at authoritative institutions like government space agencies or universities. If you are in doubt about how authoritative a source is, please ask your friendly professor in person or by email or text messages. Here are two really good ones to get you started:-

Human note

It is awkward that the word black is used in English to refer to certain physics phenomena, as well as being recruited to describe some human beings. When I am referring to a person, I use Black with a capital B as a mark of respect. When I am referring to a black hole, I use black with a small b. Regardless of my excitement level about them, black holes are less important than people.