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