1 00:00:00,000 --> 00:00:04,000 [Music throughout] How can astronomers determine 2 00:00:04,000 --> 00:00:08,000 distances in the far reaches of the universe? A small galaxy 3 00:00:08,000 --> 00:00:12,000 close in looks similar to a large galaxy farther out. 4 00:00:12,000 --> 00:00:16,000 This is real challenge that researchers have found several 5 00:00:16,000 --> 00:00:20,000 solutions for. One method uses something called a 6 00:00:20,000 --> 00:00:24,000 standard candle. A standard candle is a type of object or 7 00:00:24,000 --> 00:00:28,000 event that emits a specific, known amount of light, allowing 8 00:00:28,000 --> 00:00:32,000 scientists to find its distance with a straightforward formula. 9 00:00:32,000 --> 00:00:36,000 This works because light sources appear predictably dimmer 10 00:00:36,000 --> 00:00:40,000 the farther they are from an observer. Since astronomers know 11 00:00:40,000 --> 00:00:44,000 how much light a standard candle gives off, they can determine its distance 12 00:00:44,000 --> 00:00:48,000 by measuring how dim it appears from Earth. 13 00:00:48,000 --> 00:00:52,000 Since only very bright objects or events are visible in the 14 00:00:52,000 --> 00:00:56,000 far reaches of the universe, the options for standard candles are limited. 15 00:00:56,000 --> 00:01:00,000 Some of the best and most reliable are exploding stars, 16 00:01:00,000 --> 00:01:04,000 called supernovae. There are a few different kinds of supernovae, 17 00:01:04,000 --> 00:01:08,000 but the best for standard candles are Type Ia. These supernovae 18 00:01:08,000 --> 00:01:12,000 involve a white dwarf — the leftover core of a dead star — and 19 00:01:12,000 --> 00:01:16,000 one other star in a binary system. Some of the time 20 00:01:16,000 --> 00:01:20,000 it may be a white dwarf and larger “host” star. 21 00:01:20,000 --> 00:01:24,000 Scientists think the white dwarf steadily accumulates material shed by 22 00:01:24,000 --> 00:01:28,000 the host star, gaining mass in the process. 23 00:01:28,000 --> 00:01:32,000 When it reaches a specific tipping point, the white dwarf has gained enough 24 00:01:32,000 --> 00:01:36,000 mass to trigger a runaway reaction at its core 25 00:01:36,000 --> 00:01:40,000 and it explodes spectacularly, sending out an expanding sphere 26 00:01:40,000 --> 00:01:44,000 of super-hot material that glows from the energy of the explosion. 27 00:01:44,000 --> 00:01:48,000 28 00:01:48,000 --> 00:01:52,000 In other cases, scientists think two white dwarf stars may 29 00:01:52,000 --> 00:01:56,000 form the binary. Either the stars finally merging together 30 00:01:56,000 --> 00:02:00,000 triggers the supernova, or it happens as they spiral in 31 00:02:00,000 --> 00:02:04,000 closer and closer, while the more massive of the two pulls material 32 00:02:04,000 --> 00:02:08,000 off its companion in the final few minutes. 33 00:02:08,000 --> 00:02:12,000 Before they merge, it reaches the same mass tipping point and goes 34 00:02:12,000 --> 00:02:16,000 supernova, always releasing a similar amount of energy. 35 00:02:16,000 --> 00:02:20,000 Because white dwarf explosions are all so similar, 36 00:02:20,000 --> 00:02:24,000 the energy and light output of Type Ia supernovae are easy 37 00:02:24,000 --> 00:02:28,000 to standardize. Type Ia supernovae are rare in any one 38 00:02:28,000 --> 00:02:32,000 galaxy, occurring only once every 500 years or so in the 39 00:02:32,000 --> 00:02:36,000 Milky Way. But because there are so many galaxies, astronomers 40 00:02:36,000 --> 00:02:40,000 using current telescopes observe Type Ia supernovae about a 41 00:02:40,000 --> 00:02:44,000 hundred times a year. By comparing the observed brightness with 42 00:02:44,000 --> 00:02:48,000 the intrinsic brightness, astronomers can determine their distances 43 00:02:48,000 --> 00:02:52,000 within 6 percent. The Nancy Grace 44 00:02:52,000 --> 00:02:56,000 Roman Space Telescope, set to launch in the mid-2020s, 45 00:02:56,000 --> 00:03:00,000 will observe large patches of sky repeatedly, increasing 46 00:03:00,000 --> 00:03:04,000 the opportunities to spot these supernovae. 47 00:03:04,000 --> 00:03:08,000 Scientists predict Roman will see as many supernovae in one month 48 00:03:08,000 --> 00:03:12,000 as they’ve found in the last 20 years. 49 00:03:12,000 --> 00:03:16,000 Finding more of them will help astronomers refine the accuracy of 50 00:03:16,000 --> 00:03:20,000 this method, contribute to an improved 3-dimensional map 51 00:03:20,000 --> 00:03:24,000 of the universe, and better understand how 52 00:03:24,000 --> 00:03:28,000 the universe has expanded and evolved 53 00:03:28,000 --> 00:03:32,000 throughout cosmic history. 54 00:03:32,000 --> 00:03:36,600 [NASA] 55 00:03:36,600 --> 00:03:36,597 [NASA]