Previewing Questions

LIVE FROM A BLACK HOLE Pre-viewing Questions
Tuesday March 6, 2001 (13:00 Eastern)

1) What force of nature is primarily responsible for the existence of black holes?

Answer: (Gravity. And gravity is, in fact, the architect of the entire universe, as we'll explore more in program 2.)

2) Can a smaller object be more massive than a larger one?

Answer: (Yes. For example, a neutron star the size of Boston can have the mass of our Sun, or more.)

3) Who was the first person to think of what we now call black holes, and in which century did he or she live?

Answer: (John Michell, an 18th century English clergyman, who was previously a professor of geology at Cambridge. The French mathematician and scientists, Pierre Simon Laplace, also came up with the same idea, independently, but years after the little-known Michell.)

4) When youíve finished drinking your soda, is the can empty?

Answer: (No, it still has air compressed by Earth's atmosphere and gravity. See what happens when Pat Slane uses a vacuum pump to drain all of the air from a 55-gallon oil drum in today's program. A follow-up question might be to ask students how this is the same/different from what happens in the collapse of a star's core. We'll soon post a link to activities you can do in class, without the 55 gallon drum, that are equivalent.)

5) Name 4 kinds of light you canít see.

Answer: (Radio, microwave, infrared, ultraviolet, x-rays, gamma rays. One of the key points of today's program is that radio waves, etc. are also "light"--electromagnetic radiation. )

6) Name two of the "Great Observatories" which see some of that otherwise invisible light?

Answer: (The Hubble Space Telescope, still operating superbly well, and the Compton Gamma Ray Observatory, now safely de-orbited.)

7) If we canít see black holes, how can we see them?

Answer: (By their effect on things we can see, whether stars orbiting them--through gravity, as explained by Jeff McClintock-or by how their gravity causes infalling matter to heat up and glow in x-rays-as explained by Steve Murray and Andrea Prestwich. The relationship of kinetic and heat energy is one of the standards which looking at black holes will help you cover.)

8) If you see a star vary in brightness quickly does that means itís very small or very large?

Answer: (Very small. It would take a long time for change to affect the full sphere of a large star. This is another clue astronomers use.)

9) Stephen Murray says he likes playing "Sherlock Holmes" in search of clues to study black holes: what are some of the clues that make him and Mike Garcia know theyíre seeing black holes?

Answer: (Very large gravity condensed into a very small space. Those are the key characteristics which all black holes share, whether they are steller-mass, mid-mass or supermassive. An additional clue is extreme brightness also originating from a small region of space.)

10) How far away can Chandra's mirrors let you read a STOP sign?

Answer: (12 miles)

11) Are blue stars hotter than yellow stars, or vice versa?

Answer: (Blue stars are hotter than yellow stars.)

12) Are X-rays produced at high, or low, temperatures?

Answer: (high temperatures)

13) How fast does Earth orbit the Sun? (In kilometers per second, please.)

Answer: (KMS per second)

14) What's the formula with which we can "weigh" a black hole?

Answer: (Mass is proportional to period multiplied by velocity cubed. Math teachers among you may say, correctly, that proportionality is not a true formula with an equals sign, and therefore we are not "weighing" a black hole. That is true, but working with Jeff McClintock, P2K tried to simplify the underlying formula so that it really did seem comprehensible for middle-schoolers. We took some liberties we hope you find acceptable. We think the key idea--that you can actually weigh a black hole--is the most important aspect of this sequence. Those who want to know more, or high school students, will soon be able to find out more online via the P2K website.)