Black holes and gravity

Black holes formed from dying massive stars are the densest things in the universe. They have ten to 100 times the mass of the Sun crammed into a space that is only tens of miles across. Black holes get their name because their gravity is so strong that not even light can escape, so they look black to us. However, even though light can’t escape from inside the event horizon, we still know where lots of them are. Scientists can find and study black holes from effects they have on the space environment around them. In the talk I’ve prepared for grades 6-12, I’ll tell you about the six ways we have of finding black holes and learning more about their extreme physics. I strongly encourage teachers to show this Crash Course Astronomy video on black holes to their students before we meet.

To accompany the presentation for in-person visits, I’ve prepared an interactive lesson for middle schoolers (grades 6-8; ages 11-14) on gravity, one of the four fundamental forces of nature. The lesson teaches students that the gravity of black holes and the gravity that governs our Solar System is the same force, but the mass and compactness(/density) of the central object are what change the strength of the gravitational pull. We also discuss mass versus weight, the size of the Solar System scaled to a football field, and what would happen if the Sun were magically replaced by a black hole of the exact same mass. The material covered in this lesson is drawn heavily from this lesson from AstroEDU and meets a Michigan Department of Education Science Performance Expectation.

Objects of different masses and sizes bending the imaginary fabric of space with their gravitational pull.
Image credit: J. Provost/

The students alternate between filling in a worksheet and trying out the concepts with hands-on demonstrations. I provide “the fabric of spacetime” (big embroidery hoops with stretchy fabric) and small balls of different sizes and masses for the students to work in small groups.

Middle school student worksheet to accompany the lesson and activity.

Please contact me if you are a teacher interested in having this lesson for your class!

Header image: A simulated black hole with an accretion disk. Image credit: NASA/GSFC/J. Schnittman.