# Black Hole Orbits

## Summary:

Students are introduced to the basic properties, behavior and detection of black holes through a brief discussion of common conceptions and misconceptions of these exciting objects. They "act out" a way black holes might be detected through their interaction with other objects. In this activity, girls represent binary star systems in pairs, walking slowly around one another in a darkened room with each pair holding loops of wire to simulate the gravitational interaction. Most of the students are wearing glow-in-the-dark headbands to simulate stars, some are without headbands to represent black holes, and a small set of the black holes have flashlights to simulate X-ray emission.

## Audience:

A group of 20-25 students (grade range 5th-7th)

## Objectives:

• Explain the basic properties of black holes, including
• Escape velocity
• Gravitational interactions
• Accretion disks
• Demystify black holes
• Brainstorm with students ways they might observe objects or phenomena which cannot be seen directly
• Introduce basic X-ray physics

## Materials:

• Tennis ball
• Set of density blocks (objects of the same size and different weights)
• 5-6 loops of heavy gauge wire, ~36 inches in circumference
• 5-6 loops of heavy gauge wire, ~60 inches in circumference
• Glow-stick necklaces (one per student)
• 6 flashlights with batteries
• Cellophane or tissue paper to cover flashlight lenses
• Tissue paper party decorations
• 2 large (~ 8 inch diameter) balls
• 1 large (~ 24 inch diameter) disk

## Preparation:

1. Wire loops: ~10 minutes

Cut and shape the wire into 5-6 medium sized loops (approximately 36 inches in circumference) and 5-6 large loops (approximately 60 inches in circumference). Make a figure 8 shape with both loop sizes, attaching two of the same size together. The students will use this to simulate the gravitational pull at different distances between stars and black holes.

2. Flashlights: ~5 minutes

Cover the lenses of the flashlights with cellophane or tissue paper, and tape this into place.

3. Darken the room: variable

The room should be capable of going from brightly lit to dark so that the glow stick necklaces can be seen effectively. Sometimes this means lights or light leaks must be covered. Dark black plastic trash bags and duct tape have proven useful for this. A ladder is often required to reach the lights in an institutional building with high ceilings. The assistance of a custodian or building manager is often required, so it is important to arrange for this in advance, and to return the room to the original condition when finished.

A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC