1 00:00:00,000 --> 00:00:04,000 The Universe is vast and mysterious. 2 00:00:04,000 --> 00:00:13,000 To uncover its secrets we use telescopes like Hubble, but nature has some tricks of its own to help us on our way 3 00:00:13,000 --> 00:00:19,000 tricks of the light that mean we can see very faint and distant galaxies — 4 00:00:19,000 --> 00:00:22,000 galaxies we wouldn’t be able to see otherwise. 5 00:00:39,000 --> 00:00:44,000 Episode 70: Peering around cosmic corners 6 00:00:45,000 --> 00:00:50,000 Presented by Dr J, aka Dr Joe Liske 7 00:00:52,000 --> 00:00:57,000 Hi everyone, and welcome to another episode of the Hubblecast! 8 00:00:57,000 --> 00:01:01,000 Hubble has produced some of the very deepest images of the Universe ever 9 00:01:01,000 --> 00:01:05,000 but even these extraordinary images have their limitations. 10 00:01:05,000 --> 00:01:14,000 We know that there are galaxies that are simply too distant, and therefore too faint, to show up even in these extremely deep images. 11 00:01:14,000 --> 00:01:16,000 So what can we do? 12 00:01:16,000 --> 00:01:24,000 Well, we can either build a bigger telescope, or we can be clever and use one of nature’s telescopes 13 00:01:24,000 --> 00:01:28,000 I’m talking about a phenomenon called gravitational lensing. 14 00:01:30,000 --> 00:01:33,000 Take something like a galaxy. 15 00:01:33,000 --> 00:01:41,000 Full of stars, gas, dark matter, and dust, this galaxy’s gravitational force is so enormous 16 00:01:41,000 --> 00:01:48,000 that it affects the region it sits in and distorts the very fabric of the surrounding space. 17 00:01:50,000 --> 00:01:54,000 It isn’t only galaxies that do this. 18 00:01:54,000 --> 00:02:04,000 Any object that has mass distorts the space around it with its gravity, from large galaxy clusters down to individual stars. 19 00:02:08,000 --> 00:02:13,000 In space, light travels invariably along straight lines. 20 00:02:13,000 --> 00:02:15,000 But what is a straight line? 21 00:02:15,000 --> 00:02:18,000 Well, it is the shortest distance between two points. 22 00:02:18,000 --> 00:02:26,000 But in a curved space, the shortest distance between two points may not necessarily look particularly straight to us. 23 00:02:27,000 --> 00:02:37,000 Now what that means is that when a light ray passes very near by a massive object that curves the space around it, the light ray is bent 24 00:02:37,000 --> 00:02:45,000 As a result, the object, or rather the curved space around it produced by its gravity, acts like a lens; 25 00:02:45,000 --> 00:02:52,000 a gravitational lens that deflects light into our telescopes that would have otherwise never made it there. 26 00:02:55,000 --> 00:03:04,000 This deflection means that distant and faint objects can suddenly be seen peeking from around the edge of a nearer “lens” 27 00:03:04,000 --> 00:03:08,000 although they may look quite different than expected. 28 00:03:10,000 --> 00:03:18,000 We see distant galaxies that have been “lensed” as arcs on the sky around their lenses 29 00:03:18,000 --> 00:03:30,000 For example, the arc around this galaxy cluster is not a photographic error, but a second more distant galaxy – deformed, but visible. 30 00:03:32,000 --> 00:03:40,000 Or, if everything is perfectly aligned, we see a ring of light encircling the huge galaxy in the foreground 31 00:03:40,000 --> 00:03:51,000 These perfect rings — known as Einstein rings — are so rare that only a few handfuls have ever been observed in visible light. 32 00:03:56,000 --> 00:04:02,000 A few years ago Hubble observed an even rarer cosmic coincidence — 33 00:04:02,000 --> 00:04:13,000 an incredible double ring, where Hubble can see the light from not one but two galaxies, perfectly aligned behind a closer galaxy. 34 00:04:16,000 --> 00:04:20,000 Lensing can create weird and amusing shapes. 35 00:04:21,000 --> 00:04:25,000 Take Hubble’s image of galaxy cluster Abell 68. 36 00:04:25,000 --> 00:04:33,000 The central part of this image is distorted and stretched out into streaks by the cluster’s lensing effects 37 00:04:33,000 --> 00:04:38,000 but visible in the top corner is a cosmic space invader! 38 00:04:38,000 --> 00:04:43,000 This deformed galaxy is actually visible twice, 39 00:04:43,000 --> 00:04:51,000 as its light is following two separate paths around a nearer elliptical galaxy before reaching us. 40 00:04:57,000 --> 00:05:02,000 Now a gravitational lens not only distorts the images of background sources into funny shapes, 41 00:05:02,000 --> 00:05:05,000 but it actually makes them brighter. 42 00:05:05,000 --> 00:05:14,000 That means that, when using a gravitational lens, we can actually see fainter, and therefore more distant objects, than would otherwise be possible. 43 00:05:14,000 --> 00:05:22,000 Also, the images are magnified, so that we can see more detail – just like when using an ordinary magnifying glass. 44 00:05:24,000 --> 00:05:30,000 This isn’t the only intriguing effect that gravitational lensing can produce 45 00:05:30,000 --> 00:05:35,000 Take these five quasars photographed by Hubble back in 2006. 46 00:05:35,000 --> 00:05:42,000 They all look very similar and close together… perhaps a little too similar. 47 00:05:42,000 --> 00:05:55,000 In fact, these are not quasar quintuplets, but a single quasar seen five separate times as its light is lensed by a huge cluster of galaxies lying in the foreground. 48 00:05:56,000 --> 00:06:08,000 While bizarre, this multiple imaging can be very useful to astronomers, and allows us to figure out how light from the distant object has travelled to us 49 00:06:08,000 --> 00:06:21,000 These weird cosmic doppelgängers can be used to explore both the characteristics of the gravitational lens, and the Universe itself – for example, how it is expanding. 50 00:06:23,000 --> 00:06:29,000 Hubble’s Frontier Fields observing campaign, which began in October 2013, 51 00:06:29,000 --> 00:06:38,000 will combine the magnifying power of gravitational lensing with the light-collecting power of Hubble to delve even deeper into the distant Universe 52 00:06:38,000 --> 00:06:40,000 so, watch this space! 53 00:06:41,000 --> 00:06:48,000 This is Dr J, signing off for another episode of the Hubblecast. Once again, nature has surprised us beyond our wildest imagination. 54 00:06:49,000 --> 00:06:52,000 Hubblecast is produced by ESA/Hubble at the European Southern Observatory in Germany. 55 00:06:53,000 --> 00:06:57,000 The Hubble mission is a project of international cooperation between NASA and the European Space Agency. 56 00:06:59,000 --> 00:07:03,000 www.spacetelescope.org 57 00:07:05,000 --> 00:07:08,000 Transcribed by ESA/Hubble. Translation --