1 00:00:00,500 --> 00:00:05,000 An international team of astronomers using the NASA / ESA Hubble Space Telescope 2 00:00:05,000 --> 00:00:07,000 has discovered a ghostly ring of dark matter 3 00:00:07,000 --> 00:00:11,500 formed long ago during a colossal collision between two galaxy clusters. 4 00:00:12,500 --> 00:00:15,000 This is the first time that dark matter has been found 5 00:00:15,000 --> 00:00:19,500 with a distribution that differs radically from the distribution of ordinary matter. 6 00:00:37,000 --> 00:00:38,500 This is the Hubblecast. 7 00:00:38,500 --> 00:00:42,500 News and images from the NASA / ESA Hubble Space Telescope. 8 00:00:43,000 --> 00:00:46,000 Travelling through time and space with our host, Dr. J 9 00:00:46,000 --> 00:00:49,500 EPISODE 5: Hubble finds ring of dark matter. a.k.a. Dr. Joe Liske. 10 00:00:49,500 --> 00:00:51,500 Hello and welcome to the Hubblecast. 11 00:00:52,500 --> 00:00:55,500 Scientists reckon that most of the matter in the universe 12 00:00:55,500 --> 00:00:57,500 is something called "dark matter", 13 00:00:57,500 --> 00:01:01,500 an unknown type of matter that neither emits nor reflects light. 14 00:01:02,500 --> 00:01:04,500 But does dark matter really exist? 15 00:01:05,500 --> 00:01:07,500 Can scientists prove it? 16 00:01:07,500 --> 00:01:11,500 The NASA / ESA Hubble Space Telescope is helping to answer these questions. 17 00:01:14,500 --> 00:01:17,500 In 2004 an international team of astronomers 18 00:01:17,500 --> 00:01:21,500 pointed Hubble towards the constellation of Pisces, the Fish, 19 00:01:21,500 --> 00:01:25,000 to observe a galaxy cluster that goes by the telephone number 20 00:01:25,000 --> 00:01:32,000 of CLOO24+17 and which is located 5 billion light years away from Earth. 21 00:01:44,000 --> 00:01:49,000 Now, Hubble's Advanced Camera for Surveys produced a stunning image of this cluster. 22 00:01:49,000 --> 00:01:52,500 The galaxies in the cluster are seen here in yellow. 23 00:01:55,000 --> 00:01:57,500 Analysing the image of the last couple of years 24 00:01:57,500 --> 00:02:01,500 the team discovered a ring of dark matter, seen here in blue, 25 00:02:01,500 --> 00:02:05,500 and realized that the position of this ring did not match at all 26 00:02:05,500 --> 00:02:09,000 the position of hot gas and the galaxies in the cluster. 27 00:02:09,500 --> 00:02:13,000 The ring itself is 2.6 million light years across. 28 00:02:14,000 --> 00:02:17,000 This is the first time that dark matter has been found 29 00:02:17,000 --> 00:02:22,000 with a distribution that is so radically different from the distribution of the ordinary matter. 30 00:02:23,000 --> 00:02:26,500 This remarkable finding is attributed to the collision of the cluster 31 00:02:26,500 --> 00:02:29,500 with another cluster between 1 and 2 billion years ago. 32 00:02:29,500 --> 00:02:34,500 The team's computer simulation show, here seen from the side, 33 00:02:34,500 --> 00:02:37,000 that when the two clusters smashed together, 34 00:02:37,000 --> 00:02:41,500 the dark matter fell to the center of the combined cluster and bounced back out. 35 00:02:43,500 --> 00:02:46,500 In reality the collision occurred along our line of sight 36 00:02:46,500 --> 00:02:48,500 so that we have a head-on view of it. 37 00:02:49,500 --> 00:02:53,500 From this perspective, the dark matter structure looks like a ring, 38 00:02:53,500 --> 00:02:55,500 just as the new analysis shows. 39 00:02:57,500 --> 00:03:00,500 So how did astronomers spot this ring of dark matter? 40 00:03:01,000 --> 00:03:04,000 Well, tracing dark matter is not an easy task. 41 00:03:04,500 --> 00:03:09,500 The reason is, of course, that dark matter does not emit or reflect any light. 42 00:03:10,000 --> 00:03:15,500 The most direct way of detecting its influence is to study the way its gravity deflects light. 43 00:03:16,500 --> 00:03:22,500 Now, to do this, astronomers study the faint light from galaxies that lie behind the cluster, 44 00:03:22,500 --> 00:03:27,500 and whose light gets distorted and smeared into arcs and streaks 45 00:03:27,500 --> 00:03:31,000 by the gravity of the dark mater in the foreground cluster. 46 00:03:31,000 --> 00:03:35,000 This powerful trick is called gravitational lensing. 47 00:03:36,500 --> 00:03:40,000 To illustrate this, imagine that I'm a background galaxy... 48 00:03:41,000 --> 00:03:43,000 ...being lensed... 49 00:03:44,000 --> 00:03:46,500 ...by a massive foreground cluster. 50 00:03:47,000 --> 00:03:49,000 So by mapping the distorted light 51 00:03:49,000 --> 00:03:51,500 astronomers can deduce the mass of the cluster 52 00:03:51,500 --> 00:03:56,000 and they can trace the distribution of the dark matter within the cluster. 53 00:03:56,500 --> 00:03:59,500 This amazing image shows us some spectacular examples 54 00:03:59,500 --> 00:04:02,500 of faint background galaxies that had their light bent 55 00:04:02,500 --> 00:04:05,000 by the cluster's strong gravitational field. 56 00:04:05,000 --> 00:04:08,000 One of them, located about two times farther away 57 00:04:08,000 --> 00:04:10,500 than the yellow cluster galaxies in the foreground, 58 00:04:10,500 --> 00:04:15,000 has been multiple-imaged into five separate arc-shaped components. 59 00:04:15,500 --> 00:04:20,000 Hubble's high resolution can even show the details within this background galaxy. 60 00:04:21,000 --> 00:04:26,000 The ring's discovery is among the strongest evidence that dark matter actually exists 61 00:04:26,000 --> 00:04:29,500 and it increases confidence in our current theory of gravity. 62 00:04:29,500 --> 00:04:32,500 This is Dr. J signing off for the Hubblecast. 63 00:04:32,500 --> 00:04:36,000 Once again, nature has surprised us beyond our wildest imagination... 64 00:04:38,500 --> 00:04:40,500 Hubblecast is produced by ESA / Hubble 65 00:04:40,500 --> 00:04:43,500 at the European Southern Observatory in Germany. 66 00:04:43,500 --> 00:04:45,500 The Hubble mission is a project of international cooperation 67 00:04:45,500 --> 00:04:47,500 between NASA and the European Space Agency.