What Nobody Can See: teacher key

Black Holes, grade 11 edition, written for 11th grade. Light cannot leave a black hole, yet scientists have weighed and pictured them. Read what the evidence shows and what nobody knows.

Read the book. Print this page for the key.

Questions and answers

1. According to general relativity, why can nothing leave once it is inside a black hole?
   • Space is curved so strongly that all paths lead inward (answer)
   • Black holes are very hot inside
   • Light pushes everything back in
2. Which came first, the Nobel Prize for finding the object at our galaxy's center or the picture of Sagittarius A*?
   • The picture
   • They happened together
   • The Nobel Prize (answer)
3. Why is Sagittarius A* hard to image?
   • It changes while the data are collected (answer)
   • It is hidden behind the Sun
   • It gives off no radiation
4. What did the two black holes in the first LIGO detection merge into?
   • A neutron star
   • One black hole of about 62 Suns (answer)
   • A white dwarf
5. What does confirmation mean in "first visual confirmation"?
   • A guess
   • A warning
   • Proof (answer)

Words

• relativity: Einstein's theory
• density: how packed
• exposure: long look
• merger: a joining
• confirmation: proof