WEBVTT FILE 1 00:00:00.020 --> 00:00:04.010 Music 2 00:00:04.030 --> 00:00:08.030 Music 3 00:00:08.050 --> 00:00:12.040 Narrator: In this demonstration 4 00:00:12.060 --> 00:00:16.060 you'll use balls of clay to explore how stars fuse elements inside their 5 00:00:16.080 --> 00:00:20.080 cores. Each different color represents a different element. Here, 6 00:00:20.100 --> 00:00:24.090 pink represents hydrogen, blue is helium, 7 00:00:24.110 --> 00:00:28.130 purple is carbon, orange 8 00:00:28.150 --> 00:00:32.150 is oxygen, and this tennis ball is neon. 9 00:00:32.170 --> 00:00:36.170 We'll start with hydrogen just like you've in the center of a 10 00:00:36.190 --> 00:00:40.180 young star. The inside of a star is hot and dense and all of these 11 00:00:40.200 --> 00:00:44.210 hydrogen atoms keep bumping together. Often, some of them will stick 12 00:00:44.230 --> 00:00:48.240 together, this is called fusion. 13 00:00:48.260 --> 00:00:52.260 So we squish together four pink balls representing 14 00:00:52.280 --> 00:00:56.270 hydrogen and these form a new element--helium--represented by the blue clay. 15 00:00:56.290 --> 00:01:00.290 The sun's been doing this for nearly five billion years. 16 00:01:00.310 --> 00:01:04.320 Eventually the hydrogen in the center of the star runs low and we've mostly got 17 00:01:04.340 --> 00:01:08.350 a lot of helium jostling together instead. When hydrogen fusion 18 00:01:08.370 --> 00:01:12.380 stops the star is no longer in equilibrium and the core shrinks down. 19 00:01:12.400 --> 00:01:16.400 But this makes things even hotter so the star can start to fuse helium into 20 00:01:16.420 --> 00:01:20.420 carbon. So we squish together three blue helium atoms to make one 21 00:01:20.440 --> 00:01:24.440 purple carbon atom. In the sun this 22 00:01:24.460 --> 00:01:28.460 is where things will end once the helium runs low. But if a star is 23 00:01:28.480 --> 00:01:32.480 much bigger than the sun, the core will shrink again and it will get even hotter at the center. 24 00:01:32.500 --> 00:01:36.500 Now the star can fuse together a carbon and a helium atom creating 25 00:01:36.520 --> 00:01:40.530 oxygen. So we'll squish a blue helium atom and a purple carbon 26 00:01:40.550 --> 00:01:44.560 atom and that turns into one orange oxygen atom. You can 27 00:01:44.580 --> 00:01:48.590 imagine what happens when the oxygen runs low and fusion stops once more. 28 00:01:48.610 --> 00:01:52.630 The core shrinks, things get hotter, a new fusion can begin again, 29 00:01:52.650 --> 00:01:56.650 helium an oxygen start to fuse into neon. So we squish 30 00:01:56.670 --> 00:02:00.670 a blue helium atom and an orange oxygen atom, and swap that out for a 31 00:02:00.690 --> 00:02:04.700 tennis ball that represents neon. Depending on the size of the star 32 00:02:04.720 --> 00:02:08.720 this process can continue through the periodic table up to the point where iron is formed. 33 00:02:08.740 --> 00:02:12.740 But to fuse iron you need to input energy. With energy going 34 00:02:12.760 --> 00:02:16.770 into fusion instead of coming out of it, the star can never be in equilibrium 35 00:02:16.790 --> 00:02:20.790 again and its day are numbered. 36 00:02:20.810 --> 00:02:24.810 Music 37 00:02:24.830 --> 00:02:28.870 Music 38 00:02:28.890 --> 00:02:32.733 Music