1 00:00:01,000 --> 00:00:05,000 New Hubble observations of the massive globular cluster NGC 2808 2 00:00:05,000 --> 00:00:08,500 provide evidence that it has three generations of stars 3 00:00:08,500 --> 00:00:11,500 instead of one as current theories predict. 4 00:00:35,000 --> 00:00:36,500 This is the Hubblecast. 5 00:00:36,500 --> 00:00:40,000 News and images from the NASA / ESA Hubble Space Telescope. 6 00:00:40,000 --> 00:00:44,000 Travelling through time and space with our host, Dr. J 7 00:00:44,000 --> 00:00:46,000 EPISODE 4: Hubble finds multiple stellar 'baby booms' in a globular cluster a.k.a. Dr. Joe Liske. 8 00:00:47,000 --> 00:00:49,000 Welcome to the Hubblecast. 9 00:00:50,000 --> 00:00:53,500 Globular clusters are the homesteaders of our Milky Way galaxy 10 00:00:53,500 --> 00:00:56,500 because they were born during our galaxy's formation. 11 00:00:57,500 --> 00:01:01,500 They are compact swarms of typically hundreds of thousands of stars 12 00:01:01,500 --> 00:01:03,500 that are being held together by gravity. 13 00:01:04,500 --> 00:01:08,000 Now, astronomers have long thought that globular clusters 14 00:01:08,000 --> 00:01:12,500 experienced a single baby-boom of star formation at the beginning of their lives 15 00:01:12,500 --> 00:01:15,500 and then settled in a rather quiet existence. 16 00:01:19,000 --> 00:01:22,000 New observations by the NASA / ESA Hubble Space Telescope 17 00:01:22,000 --> 00:01:25,000 is showing that this idea may be too simple. 18 00:01:25,500 --> 00:01:30,500 The Hubble analysis of the massive globular cluster NGC 2808 19 00:01:30,500 --> 00:01:35,500 is providing evidence that instead of having one baby-boom of star formation 20 00:01:35,500 --> 00:01:38,500 star birth went "boom, boom, boom", 21 00:01:38,500 --> 00:01:43,000 creating three generations of stars earlier in the cluster's life. 22 00:01:43,000 --> 00:01:46,500 We were really shocked by the result. 23 00:01:46,500 --> 00:01:51,500 When we saw for the first time the scene we said: WOW! 24 00:01:51,500 --> 00:01:54,500 Because, I mean, we were not expecting anything like that. 25 00:01:56,000 --> 00:02:01,500 The picture that we had in mind was that globular clusters were simple stellar systems. 26 00:02:01,500 --> 00:02:07,000 Simple because all stars which have been formed all together at the same time, 27 00:02:07,000 --> 00:02:13,500 from the same material, with the same composition, and stars which are all at the same distance. 28 00:02:14,500 --> 00:02:19,000 I think this is going to change our view of globular clusters. 29 00:02:19,000 --> 00:02:25,000 And... in this sense it's a ??? of results. 30 00:02:26,500 --> 00:02:29,500 The astronomers used Hubble's Advanced Camera for Surveys 31 00:02:29,500 --> 00:02:32,500 to measure the brightness, seen along this axis. 32 00:02:32,500 --> 00:02:38,500 and the colour of the cluster stars, seen here, with blue to the left and red to the right. 33 00:02:39,000 --> 00:02:42,500 The measurement showed three distinct populations, 34 00:02:42,500 --> 00:02:45,500 with each successive generation appearing slightly bluer. 35 00:02:46,000 --> 00:02:49,500 This colour difference suggests that successive generations 36 00:02:49,500 --> 00:02:52,500 contain a slightly different mix of some chemical elements. 37 00:02:56,500 --> 00:03:00,000 We don't really know how it happened, but it may well be that the cluster 38 00:03:00,000 --> 00:03:04,500 from a first generation expelled a lot of material that only later 39 00:03:04,500 --> 00:03:10,000 fell down forming a second generation of stars with completely different chemical properties. 40 00:03:10,000 --> 00:03:13,000 This meet just an explanation and may be consistent with the fact 41 00:03:13,000 --> 00:03:17,000 that NGC 2808 is one of the most massive clusters in the galaxy, 42 00:03:17,000 --> 00:03:19,000 able to retain all this gas. 43 00:03:21,500 --> 00:03:26,500 Astronomers commonly believed that globular clusters produced only a single stellar generation, 44 00:03:27,000 --> 00:03:30,000 because the energy from that first batch of stars 45 00:03:30,000 --> 00:03:33,500 cleared out the remaining gas needed for more stars. 46 00:03:34,000 --> 00:03:38,000 But a hefty cluster, like NGC 2808, 47 00:03:38,000 --> 00:03:42,500 which is two to three times more massive than a typical globular clusters, 48 00:03:42,500 --> 00:03:45,500 may have enough gravity to hold on to that gas. 49 00:03:47,000 --> 00:03:50,500 Although the astronomers have searched only two globular clusters 50 00:03:50,500 --> 00:03:54,500 for multiple stellar generations, they say this may be a typical occurrence 51 00:03:54,500 --> 00:03:57,000 in other massive clusters as well. 52 00:03:57,000 --> 00:04:00,000 Now, no one is taking the radical step of suggesting 53 00:04:00,000 --> 00:04:03,200 that previous work on other clusters is no longer valid. 54 00:04:04,200 --> 00:04:05,700 But this discovery does show 55 00:04:05,700 --> 00:04:10,000 that the study of stellar populations in globular clusters 56 00:04:09,000 --> 00:04:11,500 may be heading in a new direction. 57 00:04:13,000 --> 00:04:17,000 The team plans to use ESO's Very Large Telescope in Chile 58 00:04:17,000 --> 00:04:20,500 to study the chemical composition of NGC 2808 59 00:04:20,500 --> 00:04:25,000 This may offer further evidence that the stars were formed at different times 60 00:04:25,000 --> 00:04:27,500 and may yield clues as to how they formed. 61 00:04:29,000 --> 00:04:32,500 The team will also use Hubble to hunt for multiple generations 62 00:04:32,500 --> 00:04:35,500 in about ten more hefty globular clusters. 63 00:04:37,000 --> 00:04:40,000 This is Dr, J signing off for the Hubblecast 64 00:04:40,000 --> 00:04:42,500 Once again, you've guessed it, 65 00:04:42,500 --> 00:04:45,500 nature has surprised us beyond our wildest imagination... 66 00:04:47,000 --> 00:04:49,000 Hubblecast is produced by ESA / Hubble 67 00:04:49,000 --> 00:04:51,500 at the European Southern Observatory in Germany. 68 00:04:52,000 --> 00:04:55,000 The Hubble mission is a project of international cooperation 69 00:04:55,000 --> 00:04:57,000 between NASA and the European Space Agency.