1 00:00:02,000 --> 00:00:07,000 3.2 billion light-years from Earth a group of astronomers have captured live with Hubble 2 00:00:07,000 --> 00:00:10,000 something they never thought they would get to see 3 00:00:24,000 --> 00:00:26,000 This is the Hubblecast! 4 00:00:26,000 --> 00:00:35,000 News and Images from the NASA/ESA Hubble Space Telescope. Travelling through time and space with our host Doctor J. 5 00:00:38,000 --> 00:00:42,000 There are many galaxies of different shapes and sizes in the universe around us today. 6 00:00:43,000 --> 00:00:49,000 Roughly half are gas-poor elliptical-shaped galaxies with few new stars forming today, 7 00:00:49,000 --> 00:00:57,000 whereas the other half are gas-rich spiral and irregular galaxies with lots of new star formation activity. 8 00:00:57,000 --> 00:01:04,000 Now observations have shown that gas-poor galaxies are most often found near the centres of rich galaxy clusters, 9 00:01:04,000 --> 00:01:08,000 whereas the spirals spend most of their life in solitude. 10 00:01:09,000 --> 00:01:14,000 However, observations of the deep and very far away Universe have also shown that 11 00:01:14,000 --> 00:01:19,000 when the Universe was roughly half of its present age, things were very different. 12 00:01:19,000 --> 00:01:24,000 Back then, only one in ten galaxies was a gas-poor one. 13 00:01:24,000 --> 00:01:29,000 So the question is, where did all of today’s gas-poor galaxies come from? 14 00:01:29,000 --> 00:01:33,000 Apparently there must have been some kind of transformation process, 15 00:01:33,000 --> 00:01:41,000 but because galaxy evolution takes place over billions of years, astronomers have so far, not been able to see it “live”. 16 00:01:43,000 --> 00:01:50,000 New observations with Hubble by an international team led by Luca Cortese of Cardiff University, United Kingdom, 17 00:01:50,000 --> 00:01:54,000 provide one of the best examples to date of this metamorphosis. 18 00:01:56,000 --> 00:02:05,000 “Well we were looking at the Abell cluster 2667, and we realized that this galaxy was falling into the clusters centre 19 00:02:05,000 --> 00:02:08,000 at a velocity of approximately 3.5 million km/hr." 20 00:02:09,000 --> 00:02:19,000 Abell 2667’s enormous gravitational field is generated by the combined contribution of the cluster’s dark matter, hot gas and hundreds of galaxies. 21 00:02:21,000 --> 00:02:29,000 As the galaxy ploughs through the cluster its gas and stars are being stripped away by the hot plasma in the cluster, 22 00:02:29,000 --> 00:02:33,000 which can reach temperatures as high as 10 to 100 million degrees. 23 00:02:33,000 --> 00:02:39,000 Also contributing to this destructive process are the tidal forces exerted by the cluster. 24 00:02:39,000 --> 00:02:45,000 These are just like the tidal forces of the moon and Sun which push and pull the Earth's oceans. 25 00:02:46,000 --> 00:02:58,000 Both processes – the tidal forces and the aptly named “ram pressure stripping” resulting from the action of the hot cluster gas - resemble those affecting comets in our Solar System. 26 00:02:58,000 --> 00:03:04,000 For this reason, scientists have nicknamed this peculiar spiral with its tail the “Comet Galaxy”. 27 00:03:05,000 --> 00:03:12,000 “We see a unique galaxy that has been transformed by the fact it's falling toward the cluster's centre." 28 00:03:12,000 --> 00:03:22,000 "And what we see exactly, it's kind of a spiral galaxy, with lots of gas and we see a trail of stars, of blue forming stars" 29 00:03:22,000 --> 00:03:31,000 "And also around those stars some kind of wispy gas stripped away by the force." 30 00:03:32,000 --> 00:03:40,000 Furthermore millions of now homeless stars have been snatched away from their mother galaxy, which will lead it to age prematurely. 31 00:03:42,000 --> 00:03:48,000 Even though its mass is slightly larger than that of the Milky Way, the spiral will inevitably lose all its gas and dust, 32 00:03:48,000 --> 00:03:57,000 and hence its chance of generating new stars later, so it will probably become a gas-poor galaxy left with an old population of red stars. 33 00:03:58,000 --> 00:04:05,000 However, in the midst of all this destruction, the cluster’s strong tidal forces have triggered a baby-boom of star formation. 34 00:04:05,000 --> 00:04:12,000 Hubble’s sharp eyes have caught other spectacular effects of Abell 2667’s immense mass. 35 00:04:12,000 --> 00:04:19,000 The giant bluish arc seen just off-centre is the magnified and distorted image of a distant background galaxy 36 00:04:19,000 --> 00:04:25,000 seen through the gravitational lens formed by the tremendous mass concentration of the cluster. 37 00:04:25,000 --> 00:04:34,000 At the cluster’s centre another rare feature can be seen: the vivid blue light from millions of stars created in a so-called cooling flow. 38 00:04:34,000 --> 00:04:41,000 Some of the hot cluster gas is cooling in a filamentary structure as it falls into the cluster’s core, 39 00:04:41,000 --> 00:04:45,000 setting off the birth of lots of bright blue stars outshining their environment. 40 00:04:45,000 --> 00:04:49,000 This may be the clearest picture of this phenomenon yet. 41 00:04:51,000 --> 00:04:59,000 By combining the visible, infrared and x-ray views from Hubble, Spitzer, Chandra, the VLT and Keck, 42 00:04:59,000 --> 00:05:04,000 we can see that this discovery adds a new brush-stroke to a painting 43 00:05:04,000 --> 00:05:10,000 where galaxies are being slowly shaped by their violent interactions with the cluster environment. 44 00:05:10,000 --> 00:05:17,000 Although there are many discoveries still to come, the emerging elements shed new light on the painting’s mysterious nature 45 00:05:17,000 --> 00:05:21,000 and are revealing some of its hidden wonders. 46 00:05:23,000 --> 00:05:26,000 This is Dr J signing off for the Hubblecast. 47 00:05:26,000 --> 00:05:31,000 Once again nature has surprised us beyond our wildest imagination … 48 00:05:32,000 --> 00:05:37,000 Hubblecast is produced by ESA/Hubble at the European Southern Observatory in Germany. 49 00:05:37,000 --> 00:05:40,000 The Hubble mission is a project of international cooperation between NASA and the European Space Agency.