WEBVTT FILE 1 00:00:00.020 --> 00:00:12.020 Music 2 00:00:12.040 --> 00:00:16.040 Narrator: In this activity, you'll model and measure the collapse of a large star to 3 00:00:16.060 --> 00:00:20.060 understand the important role of density in black holes. You'll need a 4 00:00:20.080 --> 00:00:24.080 latex balloon, blown-up to 6-8 inches in diameter, a few 5 00:00:24.100 --> 00:00:28.140 sheets of aluminum foil, a digital scale, 6 00:00:28.160 --> 00:00:32.200 a flexible tape measure, 7 00:00:32.220 --> 00:00:36.250 and a pair of scissors, or another sharp implement. 8 00:00:36.270 --> 00:00:40.320 Completely wrap the balloon in the aluminum foil, when you're done wrapping, you don't 9 00:00:40.340 --> 00:00:44.400 want to see any of the balloon peeking out. It may take a few sheets of foil to 10 00:00:44.420 --> 00:00:48.480 do this, depending on the size of the balloon, so use whatever you need. This 11 00:00:48.500 --> 00:00:52.520 foil-wrapped balloon represents a large star. 12 00:00:52.540 --> 00:00:56.560 Measure the circumference of the balloon with the tape measure and weigh the balloon on the scale. Record your 13 00:00:56.580 --> 00:01:00.600 baseline measurements. Gently squeeze the balloon, here 14 00:01:00.620 --> 00:01:04.710 you are the giant "hands" of gravity and the balloon should resist being squeezed 15 00:01:04.730 --> 00:01:08.790 because of the air pressure within the balloon. This is similar to what happens 16 00:01:08.810 --> 00:01:12.860 during the normal life a star, when gravity is balanced by fusion energy 17 00:01:12.880 --> 00:01:16.870 created at the core of the star. Now you're ready to simulate the end of the star's 18 00:01:16.890 --> 00:01:20.900 life as it runs out of fuel and that balance is broken. Pop the balloon 19 00:01:20.920 --> 00:01:25.040 carefully, trying not to crush the aluminum foil as you pop it. 20 00:01:25.060 --> 00:01:29.070 Be the hands of gravity again and gently squeeze the aluminum ball. 21 00:01:29.090 --> 00:01:33.090 This time, it doesn't push back. Make it about an inch smaller, 22 00:01:33.110 --> 00:01:37.140 keeping it as round as possible. Again, measure its circumference and weight, 23 00:01:37.160 --> 00:01:41.180 and record your new measurements. You'll repeat 24 00:01:41.200 --> 00:01:45.220 those steps a few more times, crushing down the foil ball about an inch more between measurements. 25 00:01:45.240 --> 00:01:49.250 For you final measurement, crush the ball as much as you possibly can, 26 00:01:49.270 --> 00:01:53.280 while keeping it round. Take one final measurement of its circumference and weight. 27 00:01:53.300 --> 00:01:57.320 You'll see that even though the size of the ball changed, its mass did not. 28 00:01:57.340 --> 00:02:01.350 This means that it just got more and more dense, like when a star collapses 29 00:02:01.370 --> 00:02:03.370 into a black hole. 30 00:02:03.390 --> 00:02:15.265 Music