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Narrator: In this activity, you'll model and measure the collapse of a large star to

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understand the important role of density in black holes. You'll need a

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latex balloon, blown-up to 6-8 inches in diameter, a few

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sheets of aluminum foil, a digital scale,

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a flexible tape measure,

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and a pair of scissors, or another sharp implement.

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Completely wrap the balloon in the aluminum foil, when you're done wrapping, you don't

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want to see any of the balloon peeking out. It may take a few sheets of foil to

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do this, depending on the size of the balloon, so use whatever you need. This

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foil-wrapped balloon represents a large star.

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Measure the circumference of the balloon with the tape measure and weigh the balloon on the scale. Record your

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baseline measurements. Gently squeeze the balloon, here

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you are the giant "hands" of gravity and the balloon should resist being squeezed

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because of the air pressure within the balloon. This is similar to what happens

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during the normal life a star, when gravity is balanced by fusion energy

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created at the core of the star. Now you're ready to simulate the end of the star's

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life as it runs out of fuel and that balance is broken. Pop the balloon

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carefully, trying not to crush the aluminum foil as you pop it.

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Be the hands of gravity again and gently squeeze the aluminum ball.

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This time, it doesn't push back. Make it about an inch smaller,

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keeping it as round as possible. Again, measure its circumference and weight,

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and record your new measurements. You'll repeat

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those steps a few more times, crushing down the foil ball about an inch more between measurements.

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For you final measurement, crush the ball as much as you possibly can,

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while keeping it round. Take one final measurement of its circumference and weight.

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You'll see that even though the size of the ball changed, its mass did not.

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This means that it just got more and more dense, like when a star collapses

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into a black hole.

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