Weighing the Unseen: teacher key

Black Holes, grade 9 edition, written for 9th grade. Scientists cannot see a black hole, yet they can weigh one. Read how stars, shadows and ripples in space give them numbers.

Read the book. Print this page for the key.

Questions and answers

1. Who shared half of the 2020 Nobel Prize in Physics for finding a compact object at the center of our galaxy?
   • Genzel and Ghez (answer)
   • Einstein and Michell
   • Hawking and Newton
2. The shadow of M87's black hole is about 38 billion kilometers across. About how wide is the black hole's actual surface?
   • About 76 billion kilometers
   • About 19 billion kilometers (answer)
   • About 38 billion kilometers
3. Why is Sagittarius A* hard to image?
   • It is too far away to aim at
   • It never gives off heat
   • It changes while the data are collected (answer)
4. What did detectors in Louisiana and Washington catch on September 14, 2015?
   • Ripples from two black holes crashing together (answer)
   • A picture of Sagittarius A*
   • A star falling apart
5. What does estimated mean in "first estimated from the motion of stars"?
   • Photographed
   • Exactly measured
   • Roughly worked out (answer)

Words

• shadow: dark middle
• exposure: long look
• estimated: roughly worked out
• accretion: falling together
• orbit: move around