1 00:00:01,589 --> 00:00:08,868 In 1919 the now famous Eddington expedition ventured out to see whether gravity can bend light 2 00:00:09,330 --> 00:00:12,649 — a major test of Einstein’s general theory of relativity. 3 00:00:14,519 --> 00:00:22,200 By viewing a total solar eclipse, they showed that the Sun did change the path of starlight just as predicted 4 00:00:22,980 --> 00:00:26,150 — making Einstein and his theory world-famous. 5 00:00:28,980 --> 00:00:33,500 Now, a whole century later, scientists have set out again, 6 00:00:33,500 --> 00:00:38,500 to even more remote locations scattered across four continents. 7 00:00:38,940 --> 00:00:42,590 They will once more push the limits of astronomical knowledge, 8 00:00:43,440 --> 00:00:48,110 testing the same theory in a way Einstein could never have imagined. 9 00:00:49,800 --> 00:00:56,750 Their goal: to take a picture of a black hole, something so ambitious that it seemed impossible... 10 00:00:58,560 --> 00:01:00,560 until now! 11 00:01:08,890 --> 00:01:11,790 The story of black holes begins as a puzzle. 12 00:01:12,490 --> 00:01:19,080 In 1915 Karl Schwarzschild noticed that Einstein’s then-new general theory of relativity 13 00:01:20,290 --> 00:01:24,959 predicted the existence of strange objects known as “singularities”. 14 00:01:26,530 --> 00:01:32,040 They were places where his new equations describing gravity seemed to go haywire. 15 00:01:33,400 --> 00:01:38,819 Inside them was a bizarre place where time stopped and space became infinite... 16 00:01:40,270 --> 00:01:43,829 At the time, many scientists, including Einstein, 17 00:01:44,920 --> 00:01:48,630 considered them too strange to be worth seriously researching. 18 00:01:49,750 --> 00:01:51,869 Over the hundred years since then, however, 19 00:01:52,509 --> 00:01:57,479 evidence has piled up indicating that singularities do exist in our Universe… 20 00:01:59,950 --> 00:02:01,950 ...as black holes. 21 00:02:06,670 --> 00:02:08,530 A black hole is the most mysterious object in the Universe. 22 00:02:09,790 --> 00:02:14,500 It’s where matter gets to be in such a small space and is so dense 23 00:02:14,800 --> 00:02:17,800 that the force of gravity prevents even light from escaping. 24 00:02:18,220 --> 00:02:20,609 Now that’s a one-way door from our Universe. 25 00:02:22,390 --> 00:02:26,500 We know they sit at the hearts of galaxies 26 00:02:26,500 --> 00:02:33,000 and they drive how those galaxies grow and how those galaxies die, they swallow gas and stars up. 27 00:02:33,000 --> 00:02:37,000 They’re also these incredibly enigmatic and mysterious objects 28 00:02:37,000 --> 00:02:42,000 that live at the boundary between our two great theories of physics: 29 00:02:42,000 --> 00:02:44,500 general relativity, which describes gravity, 30 00:02:44,500 --> 00:02:48,100 and quantum mechanics, which describes the smallest things in the world. 31 00:02:49,060 --> 00:02:53,300 If you want to make a test of the fundamental theories of the Universe 32 00:02:53,300 --> 00:02:56,800 you want to go to the most extreme laboratories in the Universe, 33 00:02:56,800 --> 00:02:58,230 and a black hole is that. 34 00:02:59,590 --> 00:03:05,220 But observing this most extreme laboratory requires an extreme instrument. 35 00:03:06,220 --> 00:03:10,859 The immense gravity of black holes is an obstacle to viewing them directly. 36 00:03:11,709 --> 00:03:14,519 No light can escape from them and they are tiny — 37 00:03:15,190 --> 00:03:19,290 crushing huge amounts of matter into small points of darkness. 38 00:03:22,920 --> 00:03:27,740 Even as the existence of these strangest of objects became more widely accepted, 39 00:03:28,530 --> 00:03:31,940 seeing them directly remained an impossible dream. 40 00:03:36,990 --> 00:03:42,200 In fact, to achieve the necessary resolution to see black holes directly, 41 00:03:42,200 --> 00:03:46,520 a single telescope would need to be the size of planet Earth 42 00:03:47,160 --> 00:03:49,399 — clearly too large to be feasible. 43 00:03:51,840 --> 00:03:58,670 Instead, astronomers spent decades studying the effects that black holes have on the matter around them. 44 00:04:00,420 --> 00:04:04,900 But the dream of getting more concrete evidence of these exotic objects 45 00:04:04,900 --> 00:04:07,500 was too tempting to be simply forgotten. 46 00:04:11,070 --> 00:04:14,959 We all understand from a mathematical point of view that black holes exist, 47 00:04:15,360 --> 00:04:19,500 but to actually see something is a very visceral experience 48 00:04:19,500 --> 00:04:23,449 and I think important for science and also for us to believe in it. 49 00:04:24,960 --> 00:04:30,000 In the late 1960s, a new technique changed astronomy. 50 00:04:30,000 --> 00:04:37,340 Called very long baseline interferometry, it enabled several telescopes to observe as a team 51 00:04:38,040 --> 00:04:43,790 — creating a larger, “virtual” telescope that could overcome constraints on telescope size. 52 00:04:47,010 --> 00:04:53,480 As this method spread, it became clear that direct imaging of a black hole was a real possibility. 53 00:04:56,700 --> 00:05:03,500 In 2009, the Event Horizon Telescope project, the EHT, was born 54 00:05:03,800 --> 00:05:05,780 — to pursue this exciting goal. 55 00:05:07,700 --> 00:05:12,500 The Event Horizon Telescope collaboration is a collaboration of scientists around the world 56 00:05:12,500 --> 00:05:16,500 from many different countries, continents and institutions 57 00:05:16,500 --> 00:05:22,500 to make a telescope the size of the Earth, giving us the highest resolution there is 58 00:05:22,500 --> 00:05:27,200 that currently is achievable with telescopes of any kind. 59 00:05:27,259 --> 00:05:32,709 It was clear from the outset that the EHT would face unique hurdles. 60 00:05:33,080 --> 00:05:39,699 But “seeing is believing”, and the team was dedicated to revealing a black hole for the first time. 61 00:05:41,900 --> 00:05:46,120 To create it, eight telescopes across the world were linked together. 62 00:05:48,710 --> 00:05:55,720 ESO plays a key role in two of these telescopes, both located on the Chajnantor Plateau in Chile: 63 00:06:00,979 --> 00:06:05,300 the Atacama Large Millimeter/Submillimeter Array — ALMA — 64 00:06:05,300 --> 00:06:11,100 and the Atacama Pathfinder Experiment, known as APEX. 65 00:06:13,460 --> 00:06:19,810 The other telescopes that make up the EHT are the IRAM 30-metre telescope in Spain, 66 00:06:20,960 --> 00:06:23,650 the Large Millimeter Telescope in Mexico, 67 00:06:25,880 --> 00:06:28,179 the Submillimeter Telescope in Arizona, 68 00:06:31,010 --> 00:06:33,429 the James Clerk Maxwell Telescope 69 00:06:36,210 --> 00:06:40,289 and the Submillimeter Array, both in Hawai’i, 70 00:06:42,940 --> 00:06:46,619 and finally the South Pole Telescope in Antarctica. 71 00:06:48,400 --> 00:06:56,340 Together, they can achieve a resolution equivalent to reading a newspaper in Paris while sitting in New York. 72 00:06:58,479 --> 00:07:01,859 The immense challenges of the project soon became clear. 73 00:07:02,410 --> 00:07:08,459 The telescopes, all highly-advanced instruments in their own right, were not built to work together. 74 00:07:09,849 --> 00:07:15,719 Making them work together as one interconnected interferometer required a huge team. 75 00:07:17,830 --> 00:07:24,000 These are engineers, observers, theoreticians, and they all work together, 76 00:07:24,000 --> 00:07:29,280 not only to image the event horizon of a black hole, but also to understand what we are seeing. 77 00:07:30,729 --> 00:07:36,658 The project brought together more than 200 scientists from over 100 institutions, 78 00:07:37,509 --> 00:07:42,419 all of whom had to play things by ear as they built this brand-new organisation. 79 00:07:44,560 --> 00:07:50,519 Coordinating such a large team spread across the globe was just one of many significant challenges. 80 00:07:51,250 --> 00:07:58,200 With a project that sets new benchmarks for human ingenuity, there is plenty of scope for things to go wrong. 81 00:07:58,200 --> 00:08:02,600 And, one after another, they did... 82 00:08:03,009 --> 00:08:07,679 Equipment failures... Power failures… Not enough hard drives to store data ... 83 00:08:08,349 --> 00:08:15,179 Believe it or not, at one point, some of the scientists were even held at gunpoint during their observations... 84 00:08:16,389 --> 00:08:19,529 Soon the project was in dire straits... 85 00:08:21,909 --> 00:08:26,729 The locations of the telescope also presented huge practical challenges. 86 00:08:28,719 --> 00:08:35,699 The environments that are best for viewing the night sky are often the most difficult places to build observatories. 87 00:08:36,959 --> 00:08:40,279 The telescopes of the EHT are no exception. 88 00:08:41,250 --> 00:08:44,269 Their remote sites are scattered across four continents, 89 00:08:45,240 --> 00:08:49,800 including observatories in the barren Chilean Atacama Desert, 90 00:08:49,800 --> 00:08:53,200 on a freezing plateau in Antarctica 91 00:08:53,200 --> 00:08:55,518 and on top of a dormant volcano in Hawai’i. 92 00:08:57,779 --> 00:09:01,188 All these telescopes are located far from civilisation, 93 00:09:01,889 --> 00:09:04,639 where city lights don’t pollute the night skies. 94 00:09:05,759 --> 00:09:09,889 But, for the astronomers who ventured to the telescopes to take the data, 95 00:09:11,040 --> 00:09:13,219 isolation was the least of their troubles. 96 00:09:17,309 --> 00:09:21,500 Very dry places at high altitudes are ideal for observations, 97 00:09:21,500 --> 00:09:27,919 since they avoid water vapour in the atmosphere interfering with the light from astronomical objects. 98 00:09:30,720 --> 00:09:34,200 ALMA and APEX are located on the Chajnantor Plateau, 99 00:09:34,200 --> 00:09:40,000 at an altitude of 5000 metres in the barren Chilean Atacama Desert, 100 00:09:40,000 --> 00:09:45,559 a place so inhospitable that it serves as testing ground for Mars rovers. 101 00:09:48,600 --> 00:09:54,019 People working here had to use oxygen tanks as the air is too thin to breathe. 102 00:09:58,170 --> 00:10:05,000 The dangers of altitude sickness were also shared by observers at the James Clerk Maxwell Telescope 103 00:10:05,000 --> 00:10:11,269 and the Submillimeter Array located near the summit of the dormant volcano Mauna Kea. 104 00:10:13,259 --> 00:10:17,089 In this exposed location high above sea level, 105 00:10:18,300 --> 00:10:22,039 astronomers ran the risk of serious dehydration and sunstroke. 106 00:10:23,879 --> 00:10:26,779 At the opposite extreme of the temperature scale, 107 00:10:27,959 --> 00:10:31,300 observers at the South Pole Telescope in Antarctica 108 00:10:31,300 --> 00:10:35,300 had to endure sub-zero temperatures for long stretches of time. 109 00:10:35,790 --> 00:10:38,389 Here, there were unique challenges; 110 00:10:39,089 --> 00:10:41,599 in winter the Sun never rises above the horizon, 111 00:10:42,990 --> 00:10:45,709 creating a single night that lasts for months. 112 00:10:47,399 --> 00:10:52,068 Wonderful for the telescopes, but it takes a psychological toll on humans. 113 00:10:56,100 --> 00:10:59,360 Sleepless nights were spent working in these hostile regions. 114 00:11:02,910 --> 00:11:07,500 After almost a decade of preparation, the EHT was finally ready 115 00:11:07,500 --> 00:11:11,500 to use all eight telescopes as one instrument. 116 00:11:11,500 --> 00:11:21,000 On 5 April 2017 the EHT was for the first time aimed at the chosen target, M87*, 117 00:11:21,000 --> 00:11:28,600 the black hole in the centre of the enormous galaxy Messier 87, about 55 million light years from Earth. 118 00:11:29,430 --> 00:11:34,500 Attempting to peer into the dark heart of a galaxy tens of millions of light years away 119 00:11:34,500 --> 00:11:36,930 might seem like a strange choice. 120 00:11:36,930 --> 00:11:39,230 There are many black holes closer to home. 121 00:11:41,460 --> 00:11:44,449 But M87* was carefully selected. 122 00:11:45,210 --> 00:11:47,210 It had two big advantages: 123 00:11:47,820 --> 00:11:50,360 It’s one of the biggest black holes known, 124 00:11:50,790 --> 00:11:56,569 giving the astronomers a better chance of seeing it than smaller black holes in our neighbourhood; 125 00:11:57,300 --> 00:11:59,779 and isn’t too far north or south in the sky 126 00:12:00,960 --> 00:12:05,960 — crucial if telescopes all over the world have to observe it at the same time. 127 00:12:07,350 --> 00:12:12,559 When those sleepless nights of observation ended, a new phase of work began. 128 00:12:13,290 --> 00:12:15,499 In order to find out what they’d seen 129 00:12:16,200 --> 00:12:20,000 the scientists had to painstakingly combine and analyse the data. 130 00:12:23,000 --> 00:12:26,689 Two computation centres, one in Europe and one in the US, 131 00:12:27,420 --> 00:12:30,679 combined a staggering quantity of data 132 00:12:30,800 --> 00:12:34,040 — about 350 terabytes per day from each telescope. 133 00:12:35,100 --> 00:12:40,000 The data had to be synchronized by atomic clocks so precise 134 00:12:40,000 --> 00:12:43,500 that they lose only 1 second every 10 million years 135 00:12:43,500 --> 00:12:48,380 and then transported on specialised helium-filled hard drives. 136 00:12:50,190 --> 00:12:54,140 Hand-carrying this precious cargo might seem like a low-tech solution, 137 00:12:54,330 --> 00:12:59,000 but the drives contained so much data that moving them by hand was, 138 00:12:59,000 --> 00:13:03,800 at times, the fastest data transmission in history. 139 00:13:07,220 --> 00:13:12,069 After countless hours of work on the data, an image began to take shape. 140 00:13:12,949 --> 00:13:19,479 This image would tell hundreds of scientists whether decades of work had attained the unattainable, 141 00:13:19,880 --> 00:13:21,880 or had been in vain. 142 00:13:23,509 --> 00:13:27,000 Although black holes themselves are completely dark, 143 00:13:27,000 --> 00:13:31,500 they influence the path of photons travelling in their vicinity 144 00:13:31,500 --> 00:13:38,000 and leave an unmistakable signature on the light from the accretion disc surrounding the black hole 145 00:13:38,000 --> 00:13:41,919 — a large disc of matter gradually spiralling in towards its host. 146 00:13:42,649 --> 00:13:45,609 The infalling matter becomes very concentrated, 147 00:13:46,399 --> 00:13:49,869 causing friction to heat it to form a glowing plasma. 148 00:13:50,509 --> 00:13:55,809 The path of the light emitted by this glowing gas is determined by the black hole: 149 00:13:56,149 --> 00:14:01,479 the light passing close by it is bent by the enormous gravity, skirting the edges, 150 00:14:01,940 --> 00:14:06,159 but light passing too close is captured, never to escape. 151 00:14:06,980 --> 00:14:08,980 Seen from Earth with radio telescopes, 152 00:14:09,649 --> 00:14:14,198 these effects manifest themselves as the shadow of a black hole 153 00:14:16,459 --> 00:14:20,679 — a dark central region silhouetted against the luminous plasma. 154 00:14:28,170 --> 00:14:33,679 After 2 years of painstaking calculations, the image was finally ready…. 155 00:14:58,000 --> 00:15:01,890 Although taken from the staggering distance of 55 million light-years, 156 00:15:02,440 --> 00:15:07,000 the image revealed a ring-like structure with a dark central region. 157 00:15:07,000 --> 00:15:11,880 For the first time in history: the shadow of a black hole! 158 00:15:12,610 --> 00:15:16,400 And then we look at our first source and we see that ring. 159 00:15:16,900 --> 00:15:23,000 We see the event horizon and we see that shadow, that dark region and you know immediately 160 00:15:23,000 --> 00:15:27,870 we are looking at an event horizon at a black hole from all sides at once in this thing. 161 00:15:27,870 --> 00:15:30,400 We see at a region where time stops. 162 00:15:30,400 --> 00:15:35,900 This is a very different part of the Universe we are seeing for the very first time. 163 00:15:35,920 --> 00:15:39,600 I mean this is exactly what we have been looking for but after eight years 164 00:15:39,600 --> 00:15:44,000 and all that long process, a few weeks of imaging and they showed us exactly what we wanted. 165 00:15:44,000 --> 00:15:45,000 I couldn’t believe it. 166 00:15:47,620 --> 00:15:51,000 Well, I have to say it’s taken on a new importance now, 167 00:15:51,000 --> 00:15:55,800 as we actually have images that look like the simulations. 168 00:15:55,800 --> 00:16:00,000 There’s extraordinary confluence between theory and experiment 169 00:16:00,000 --> 00:16:03,870 and it promises tremendous breakthroughs on the horizon. 170 00:16:06,040 --> 00:16:12,750 This historic achievement is a major milestone in our evolving understanding of the Universe, 171 00:16:13,000 --> 00:16:19,500 and also sets a new precedent for global collaboration in scientific research. 172 00:16:19,810 --> 00:16:24,300 One of the most uplifting things for me is the team that we’ve built, 173 00:16:24,300 --> 00:16:28,300 and the fact that we’re doing something that people have told us was impossible, 174 00:16:28,300 --> 00:16:35,300 and when you at the end of the day do something that people tell you can’t do it’s an incredible feeling, 175 00:16:35,300 --> 00:16:39,450 and I think the whole team is very very proud that we’ve accomplished something like this. 176 00:16:39,850 --> 00:16:42,210 It’s not just for us, it’s for everyone. 177 00:16:46,980 --> 00:16:49,560 As the EHT is expanded 178 00:16:49,560 --> 00:16:55,049 it will allow us to probe the deep questions that attract researchers to black holes: 179 00:16:56,050 --> 00:17:01,740 how well do our laws of physics hold up under the most extreme conditions we know of? 180 00:17:03,040 --> 00:17:09,000 How do the mechanics of gas, radiation, and particles around a black hole work? 181 00:17:09,370 --> 00:17:15,000 Which theories are correct, and which will break down with more precise observations? 182 00:17:16,120 --> 00:17:22,049 Only time will tell which mysteries the EHT will unravel next. 183 00:17:26,520 --> 00:17:33,000 Transcribed by ESO; translated by —