1 00:00:08,310 --> 00:00:04,190 Sound effects 2 00:00:08,330 --> 00:00:12,350 silence 3 00:00:12,370 --> 00:00:16,400 Galaxies are the building blocks of the universe. 4 00:00:16,420 --> 00:00:20,420 The giant galaxies we see today — even our own — were built up 5 00:00:20,440 --> 00:00:24,560 from many smaller galaxies. But construction isn't 6 00:00:24,580 --> 00:00:28,720 done yet. It continues even today. 7 00:00:28,740 --> 00:00:32,900 Full-grown galaxies approach and interact with each other. 8 00:00:32,920 --> 00:00:36,980 They may collide and eventually merge. 9 00:00:37,000 --> 00:00:41,010 As the galaxies approach, the tug of gravity creates tides 10 00:00:41,030 --> 00:00:45,180 that distort their shapes. 11 00:00:45,200 --> 00:00:49,330 Stars and gas stream into new orbits. 12 00:00:49,350 --> 00:00:53,430 Sometimes, they're completely ejected, 13 00:00:53,450 --> 00:00:57,490 trailing into the depths of intergalactic space. 14 00:00:57,510 --> 00:01:01,540 Gas clouds compressed in the chaos light up with intense rounds 15 00:01:01,560 --> 00:01:05,560 of star formation. Because stars create most of the chemical 16 00:01:05,580 --> 00:01:09,690 elements, such episodes have a profound effect on a galaxy's 17 00:01:09,710 --> 00:01:13,840 chemical makeup. 18 00:01:13,860 --> 00:01:17,940 This infrared image of the entire sky shows half a billion 19 00:01:17,960 --> 00:01:22,010 stars. Most are in our galaxy. 20 00:01:22,030 --> 00:01:26,040 Some are not. These are companion galaxies that orbit 21 00:01:26,060 --> 00:01:30,210 our Milky Way. And some are in between. 22 00:01:30,230 --> 00:01:34,350 In 1994, astronomers 23 00:01:34,370 --> 00:01:38,470 discovered that some of these stars actually belong to ... 24 00:01:38,490 --> 00:01:42,550 ... a different galaxy. It's called the 25 00:01:42,570 --> 00:01:46,600 Sagittarius Dwarf Elliptical, and the Milky Way 26 00:01:46,620 --> 00:01:50,620 is tearing it apart. 27 00:01:50,640 --> 00:01:54,720 As the dwarf galaxy passes through the Milky Way's disk, 28 00:01:54,740 --> 00:01:58,900 gravitational tides stretch the dwarf's stars into long streams 29 00:01:58,920 --> 00:02:03,070 that wrap around the galaxy's orbit. 30 00:02:03,090 --> 00:02:07,160 For the dwarf, it's a fatal attraction. For the Milky Way, 31 00:02:07,180 --> 00:02:11,210 it's but one of many similar events that shaped our home galaxy. 32 00:02:11,230 --> 00:02:15,230 But there's something much bigger headed our way. 33 00:02:15,250 --> 00:02:19,360 M31, the Andromeda Galaxy. 34 00:02:19,380 --> 00:02:23,510 This is no dwarf. It's the Milky Way's biggest 35 00:02:23,530 --> 00:02:27,630 neighbor; of roughly the same size, mass 36 00:02:27,650 --> 00:02:31,660 and type. Astronomers say 37 00:02:31,680 --> 00:02:35,680 the crash will begin about 2 billion years from now. This 38 00:02:35,700 --> 00:02:39,810 supercomputer simulation shows how the event may unfold 39 00:02:39,830 --> 00:02:43,960 over billions of years. 40 00:02:43,980 --> 00:02:48,060 The first pass distorts the two great spirals. 41 00:02:48,080 --> 00:02:52,150 Stars are tossed into the intergalactic night like 42 00:02:52,170 --> 00:02:56,190 sparks thrown from a campfire. 43 00:02:56,210 --> 00:03:00,210 Our sun, complete with planets in tow, could be similarly 44 00:03:00,230 --> 00:03:04,360 ejected. Each pass blurs the 45 00:03:04,380 --> 00:03:08,490 identities of each galaxy. 46 00:03:08,510 --> 00:03:12,580 Eventually, Andromeda and the Milky Way will merge into a 47 00:03:12,600 --> 00:03:16,630 single entity some astronomers call "Milkomeda." 48 00:03:16,650 --> 00:03:20,670 How did the shape, structure, and chemical 49 00:03:20,690 --> 00:03:24,840 content of galaxies change over the sweep of cosmic 50 00:03:24,860 --> 00:03:28,990 history? Deep surveys by the James Webb Space 51 00:03:29,010 --> 00:03:33,130 Telescope will capture the full panorama 52 00:03:33,150 --> 00:03:37,210 from the earliest dwarfs that formed to the familiar galaxies we see around 53 00:03:37,230 --> 00:03:41,240 us today.