WEBVTT 1 00:00:07.519 --> 00:00:10.480 - Hello, and welcome to this episode of the 2 00:00:10.480 --> 00:00:12.259 - Physics World Weekly Podcast, 3 00:00:12.755 --> 00:00:15.255 - which is sponsored by the Kavli Prize. 4 00:00:15.794 --> 00:00:19.015 - The Kavli Prize honors scientists for breakthroughs 5 00:00:19.475 --> 00:00:20.454 - in astrophysics, 6 00:00:21.315 --> 00:00:21.815 - nanoscience, 7 00:00:22.195 --> 00:00:23.095 - and neuroscience, 8 00:00:24.195 --> 00:00:27.869 - transforming our understanding of the big, the small, 9 00:00:27.929 --> 00:00:28.989 - and the complex. 10 00:00:29.769 --> 00:00:32.489 - The vision for the Kavli Prize comes from 11 00:00:32.489 --> 00:00:36.030 - Fred Kavli, a Norwegian American entrepreneur 12 00:00:36.409 --> 00:00:37.309 - and philanthropist 13 00:00:38.009 --> 00:00:39.309 - who turned his lifelong 14 00:00:40.009 --> 00:00:41.390 - fascination with science 15 00:00:41.784 --> 00:00:44.524 - into a lasting legacy for recognizing 16 00:00:45.225 --> 00:00:49.085 - scientific breakthroughs and for supporting basic research. 17 00:00:49.945 --> 00:00:51.645 - The 2026 18 00:00:51.784 --> 00:00:53.484 - Kavli Prize in Astrophysics 19 00:00:54.300 --> 00:00:57.740 - was announced on June 10. And I'm very 20 00:00:57.740 --> 00:00:59.679 - pleased to be joined by the astronomer 21 00:01:00.300 --> 00:01:01.600 - Amina Helmi, 22 00:01:02.140 --> 00:01:05.120 - who shares this year's prize with Vasily 23 00:01:05.579 --> 00:01:06.079 - Bolakarov 24 00:01:06.859 --> 00:01:07.680 - and Rodrigo 25 00:01:08.060 --> 00:01:08.560 - Ibadah. 26 00:01:09.484 --> 00:01:11.725 - She joins me down the line from the 27 00:01:11.725 --> 00:01:13.025 - Kapteine Astronomical 28 00:01:13.405 --> 00:01:13.905 - Institute 29 00:01:14.284 --> 00:01:15.265 - in The Netherlands, 30 00:01:15.805 --> 00:01:18.145 - where she is professor of astronomy. 31 00:01:19.245 --> 00:01:20.944 - I would also like to welcome 32 00:01:21.325 --> 00:01:22.865 - Per Barth Lilia 33 00:01:23.245 --> 00:01:24.064 - to the podcast. 34 00:01:24.900 --> 00:01:27.480 - He is chair of the twenty twenty six 35 00:01:27.780 --> 00:01:30.120 - Kavli Prize Committee in Astrophysics 36 00:01:30.820 --> 00:01:33.299 - and speaks to us from the Institute of 37 00:01:33.299 --> 00:01:33.799 - Theoretical 38 00:01:34.260 --> 00:01:34.760 - Astrophysics 39 00:01:35.460 --> 00:01:36.200 - at Norway's 40 00:01:36.659 --> 00:01:38.040 - University of Oslo, 41 00:01:38.564 --> 00:01:40.825 - where he is professor of cosmology. 42 00:01:41.844 --> 00:01:43.144 - Amina and Per, 43 00:01:43.444 --> 00:01:44.744 - welcome to the podcast, 44 00:01:45.045 --> 00:01:46.024 - and congratulations, 45 00:01:46.484 --> 00:01:49.625 - Amina, for sharing the 2026 46 00:01:49.844 --> 00:01:51.864 - Kavli Prize in Astrophysics. 47 00:01:52.969 --> 00:01:53.870 - Thank you, Hamish. 48 00:01:54.729 --> 00:01:55.870 - Thank you for, 49 00:01:56.569 --> 00:01:57.629 - inviting me, 50 00:01:58.409 --> 00:02:01.229 - and thank you also to Per for selecting 51 00:02:02.010 --> 00:02:04.569 - us to be the winners of this year 52 00:02:04.569 --> 00:02:06.430 - for being the chair of the committee. 53 00:02:08.064 --> 00:02:10.465 - It's an enormous pleasure and an honor to 54 00:02:10.465 --> 00:02:11.365 - be here today. 55 00:02:12.305 --> 00:02:15.685 - And, Per, before we chat about Amina's work 56 00:02:15.824 --> 00:02:17.925 - and that of her fellow laureates, 57 00:02:18.544 --> 00:02:19.925 - can you give us a citation 58 00:02:20.224 --> 00:02:21.444 - for this year's prize 59 00:02:21.939 --> 00:02:24.740 - and perhaps provide a little insight into why 60 00:02:24.740 --> 00:02:25.400 - the committee 61 00:02:25.780 --> 00:02:27.080 - came to its decision? 62 00:02:28.180 --> 00:02:29.159 - Well, the citation, 63 00:02:30.180 --> 00:02:32.419 - for for the award is that it it's 64 00:02:32.419 --> 00:02:35.459 - given for uncovering the fossil evidence of past 65 00:02:35.459 --> 00:02:35.959 - mergers 66 00:02:36.405 --> 00:02:38.644 - proving that the Milky Way galaxy was built 67 00:02:38.644 --> 00:02:40.104 - through hierarchical accretion. 68 00:02:40.965 --> 00:02:44.185 - The three Kavli Prize laureates have fundamentally transformed 69 00:02:44.324 --> 00:02:45.144 - our understanding 70 00:02:45.604 --> 00:02:46.984 - of how massive galaxies 71 00:02:47.364 --> 00:02:49.625 - have evolved over the history of the universe. 72 00:02:49.860 --> 00:02:52.520 - In the hierarchical framework of galaxy formation, 73 00:02:52.979 --> 00:02:55.879 - massive galaxies are thought to grow by accreting 74 00:02:55.939 --> 00:02:57.960 - numerous smaller galactic systems 75 00:02:58.340 --> 00:02:59.960 - from their surrounding circumgalactic 76 00:03:00.419 --> 00:03:00.919 - environment. 77 00:03:01.539 --> 00:03:04.599 - The laureates have provided clear observational evidence 78 00:03:05.034 --> 00:03:05.854 - that major 79 00:03:06.555 --> 00:03:09.534 - merger events have indeed occurred, that their signatures 80 00:03:09.594 --> 00:03:12.474 - remain visible years later in our Milky Way 81 00:03:12.474 --> 00:03:12.974 - galaxy. 82 00:03:13.754 --> 00:03:14.414 - The committee, 83 00:03:15.514 --> 00:03:17.854 - has received quite a number of nominations 84 00:03:18.235 --> 00:03:20.870 - in all different fields covering 85 00:03:21.169 --> 00:03:22.870 - space science and astronomy, 86 00:03:23.169 --> 00:03:23.669 - astrophysics, 87 00:03:24.849 --> 00:03:25.349 - instrument 88 00:03:26.449 --> 00:03:26.949 - instrumentation. 89 00:03:27.569 --> 00:03:28.069 - And, 90 00:03:28.449 --> 00:03:30.129 - we had a tough job, of course, 91 00:03:30.610 --> 00:03:32.770 - which, the committee always has of, 92 00:03:33.495 --> 00:03:35.435 - narrowing down who we wanted to, 93 00:03:37.574 --> 00:03:39.974 - to give the, to give the price to 94 00:03:39.974 --> 00:03:41.594 - this year. But we found that, 95 00:03:43.655 --> 00:03:46.489 - this is really fundamental work. It's also done 96 00:03:46.489 --> 00:03:46.989 - by, 97 00:03:47.610 --> 00:03:50.409 - quite young scientists who are still in their 98 00:03:50.409 --> 00:03:51.229 - most active, 99 00:03:52.090 --> 00:03:55.129 - period their career. And we thought this would 100 00:03:55.129 --> 00:03:56.669 - be a very good, 101 00:03:57.930 --> 00:04:00.330 - signal to them and to this community. And, 102 00:04:00.330 --> 00:04:00.830 - also, 103 00:04:01.444 --> 00:04:03.064 - in addition to that, really, 104 00:04:03.764 --> 00:04:06.884 - a signal showing how important, especially the Gaia 105 00:04:06.884 --> 00:04:10.004 - space mission is, and that it's important to 106 00:04:10.004 --> 00:04:10.504 - really 107 00:04:11.204 --> 00:04:12.584 - we also would like to 108 00:04:13.060 --> 00:04:15.299 - show that this it's important to fund this 109 00:04:15.299 --> 00:04:17.240 - until the final data releases, 110 00:04:18.579 --> 00:04:20.279 - hope to come in 2030. 111 00:04:21.860 --> 00:04:24.339 - And, Amina, can you set the scene for 112 00:04:24.339 --> 00:04:25.079 - our listeners? 113 00:04:25.634 --> 00:04:27.394 - Can you give us an overview of the 114 00:04:27.394 --> 00:04:28.294 - Milky Way? 115 00:04:28.595 --> 00:04:30.675 - What shape is it? How big is it? 116 00:04:30.675 --> 00:04:33.014 - And how many stars does it contain? 117 00:04:33.555 --> 00:04:35.714 - And and how old is it? Can can 118 00:04:35.714 --> 00:04:37.875 - you give us a potted history of the 119 00:04:37.875 --> 00:04:38.774 - Milky Way? 120 00:04:39.500 --> 00:04:42.220 - Yes. Of course. So the Milky Way is, 121 00:04:42.220 --> 00:04:44.220 - as we all know, is the galaxy that 122 00:04:44.220 --> 00:04:45.040 - we live in. 123 00:04:46.220 --> 00:04:48.240 - It's about 90,000 124 00:04:48.460 --> 00:04:50.240 - light years in diameter. 125 00:04:50.939 --> 00:04:52.960 - It has about a 100,000,000,000 126 00:04:53.340 --> 00:04:54.960 - suns or stars. 127 00:04:55.855 --> 00:04:58.095 - And and it is a typical galaxy. That's 128 00:04:58.254 --> 00:04:59.555 - so that's quite interesting. 129 00:05:00.014 --> 00:05:01.394 - It's a disk galaxy. 130 00:05:03.694 --> 00:05:06.095 - The stars in the days the majority of 131 00:05:06.095 --> 00:05:07.954 - these have formed in the last, 132 00:05:08.654 --> 00:05:10.514 - about ten billion years, 133 00:05:12.330 --> 00:05:14.730 - and it's still forming stars at about the 134 00:05:14.730 --> 00:05:16.990 - rate of a few suns per year. 135 00:05:18.089 --> 00:05:20.490 - So because it's it's a typical galaxy, it 136 00:05:20.490 --> 00:05:22.110 - also gives us the the, 137 00:05:23.529 --> 00:05:26.814 - the possibility of trying to understand how galaxy 138 00:05:26.814 --> 00:05:28.595 - formation in general works. 139 00:05:28.975 --> 00:05:30.735 - But the truth is it's our home in 140 00:05:30.735 --> 00:05:32.975 - the universe, so that makes it also extra 141 00:05:32.975 --> 00:05:33.475 - interesting. 142 00:05:35.134 --> 00:05:37.055 - And and is it I mean, I would 143 00:05:37.055 --> 00:05:40.115 - assume that because we're in the Milky Way, 144 00:05:40.410 --> 00:05:43.529 - it's it's easy for us to study. But 145 00:05:43.529 --> 00:05:45.689 - but but is that the case? I mean, 146 00:05:45.689 --> 00:05:47.689 - you know, for example, we can't stand back 147 00:05:47.689 --> 00:05:48.990 - from the Milky Way 148 00:05:49.370 --> 00:05:51.790 - and and look at it from a distance 149 00:05:52.009 --> 00:05:53.790 - and sort of see it whole. 150 00:05:54.634 --> 00:05:56.875 - On the other hand, you know, it's it's 151 00:05:56.875 --> 00:05:59.615 - very all stars are very close to us. 152 00:05:59.915 --> 00:06:02.634 - So are there pros and cons in in 153 00:06:02.634 --> 00:06:04.254 - studying the Milky Way? 154 00:06:05.194 --> 00:06:07.680 - Yes. You're absolutely right. So one of the 155 00:06:07.680 --> 00:06:10.319 - things we're still struggling, for example, is to 156 00:06:10.319 --> 00:06:13.120 - understand how many spiral arms the Milky Way 157 00:06:13.120 --> 00:06:15.599 - has because they are in the disk, and 158 00:06:15.599 --> 00:06:17.839 - we're also in the disk. So we cannot 159 00:06:17.839 --> 00:06:18.740 - raise above 160 00:06:19.279 --> 00:06:20.959 - the plane and look at it from the 161 00:06:20.959 --> 00:06:21.459 - outside. 162 00:06:22.064 --> 00:06:23.264 - But like you say, 163 00:06:23.985 --> 00:06:26.324 - because we have access to, 164 00:06:27.185 --> 00:06:29.904 - information about the individual stars, we can measure 165 00:06:29.904 --> 00:06:32.305 - the properties, we can measure how fast they 166 00:06:32.305 --> 00:06:34.725 - move, where they are located in space, 167 00:06:35.180 --> 00:06:38.000 - We can measure ages and chemical compositions. 168 00:06:38.379 --> 00:06:41.839 - All of that information is really only available 169 00:06:42.300 --> 00:06:44.779 - at the moment for stars in our galaxy. 170 00:06:44.779 --> 00:06:46.540 - And so that is what allows us to 171 00:06:46.540 --> 00:06:49.360 - reconstruct the history in so much detail. 172 00:06:51.014 --> 00:06:53.675 - And, Per, you mentioned that this year's laureates, 173 00:06:54.774 --> 00:06:55.435 - have done, 174 00:06:56.454 --> 00:06:59.274 - some really, really good work on, 175 00:07:00.375 --> 00:07:01.035 - the hierarchical 176 00:07:01.814 --> 00:07:02.314 - accretion, 177 00:07:03.175 --> 00:07:05.274 - and how the Milky Way was formed 178 00:07:05.579 --> 00:07:07.819 - by this process. Can can you give us 179 00:07:07.819 --> 00:07:09.199 - a little more insight 180 00:07:09.740 --> 00:07:10.800 - into hierarchical 181 00:07:11.500 --> 00:07:12.000 - accretion? 182 00:07:12.699 --> 00:07:14.540 - How does it happen, and and why is 183 00:07:14.540 --> 00:07:15.199 - it important 184 00:07:15.660 --> 00:07:18.540 - that we understand the Milky Way was was 185 00:07:18.540 --> 00:07:19.040 - made 186 00:07:19.745 --> 00:07:20.805 - by that process. 187 00:07:21.185 --> 00:07:22.144 - Well, from the, 188 00:07:22.625 --> 00:07:24.964 - nineteen eighties, early nineteen eighties, 189 00:07:26.225 --> 00:07:26.725 - hierarchical, 190 00:07:27.584 --> 00:07:28.084 - accretion, 191 00:07:28.464 --> 00:07:29.204 - has been 192 00:07:29.824 --> 00:07:31.365 - the common theory. But, 193 00:07:31.745 --> 00:07:34.245 - that small structures form first in the universe 194 00:07:34.305 --> 00:07:35.044 - just because 195 00:07:36.120 --> 00:07:36.620 - fluctuations 196 00:07:36.920 --> 00:07:37.899 - on that scale, 197 00:07:38.439 --> 00:07:40.139 - in the density field, which 198 00:07:40.519 --> 00:07:42.060 - finally became galaxies, 199 00:07:42.600 --> 00:07:43.899 - stars, everything, 200 00:07:44.839 --> 00:07:47.240 - was stronger on the small scales than on 201 00:07:47.240 --> 00:07:50.024 - large scales. And then these merged. But we 202 00:07:50.024 --> 00:07:51.324 - haven't really seen, 203 00:07:52.504 --> 00:07:53.625 - this working in, 204 00:07:54.425 --> 00:07:55.865 - this happening in in, 205 00:07:56.745 --> 00:07:58.125 - real time. But now, 206 00:07:58.584 --> 00:08:01.324 - Amina and her colleagues, they are showing us 207 00:08:02.870 --> 00:08:05.370 - that we really see the remnants of recent 208 00:08:05.509 --> 00:08:08.170 - and ongoing such merger events now. 209 00:08:09.509 --> 00:08:12.230 - Thanks, Per. So, Amina, much of your research 210 00:08:12.230 --> 00:08:14.410 - has focused on stellar streams. 211 00:08:15.004 --> 00:08:17.664 - And I think there's actually a stellar stream 212 00:08:18.125 --> 00:08:19.425 - named after you. 213 00:08:19.805 --> 00:08:21.824 - So what is a stellar stream, 214 00:08:22.204 --> 00:08:25.104 - and why do they support the idea of 215 00:08:25.324 --> 00:08:25.824 - hierarchical 216 00:08:26.365 --> 00:08:26.865 - accretion? 217 00:08:29.220 --> 00:08:32.179 - Yes. So, indeed, there's a stream named after 218 00:08:32.179 --> 00:08:32.679 - me. 219 00:08:34.100 --> 00:08:37.080 - So so as Pero was saying, we think 220 00:08:37.220 --> 00:08:40.340 - that galaxies or we thought, from the this 221 00:08:40.340 --> 00:08:42.360 - model from the eighties that galaxies 222 00:08:43.174 --> 00:08:45.355 - must have experienced mergers 223 00:08:46.134 --> 00:08:48.235 - as they grew in mass, particularly 224 00:08:48.615 --> 00:08:49.674 - at early times. 225 00:08:50.375 --> 00:08:53.995 - And as a galaxy orbits another galaxy, 226 00:08:55.549 --> 00:08:58.509 - it loses it feels the tidal forces of 227 00:08:58.509 --> 00:09:00.209 - the bigger system, and 228 00:09:00.589 --> 00:09:03.949 - that leads to the formation of stellar streams. 229 00:09:03.949 --> 00:09:06.189 - So these are groups of stars that have 230 00:09:06.189 --> 00:09:07.889 - lost their parent system, 231 00:09:08.674 --> 00:09:10.774 - and that actually can remain coherent 232 00:09:11.075 --> 00:09:11.894 - for even, 233 00:09:12.434 --> 00:09:14.455 - the age of the universe and longer. 234 00:09:15.475 --> 00:09:16.774 - So these are basically 235 00:09:17.075 --> 00:09:17.894 - if you would, 236 00:09:19.475 --> 00:09:21.794 - make a map of the sky, you will 237 00:09:21.794 --> 00:09:22.294 - see, 238 00:09:23.059 --> 00:09:25.860 - streams of stars, so groups of stars on 239 00:09:25.860 --> 00:09:27.480 - very coherent structures. 240 00:09:29.459 --> 00:09:32.679 - And these groups of stars also share similar 241 00:09:32.740 --> 00:09:35.834 - motions because they are all lost at similar 242 00:09:35.834 --> 00:09:39.115 - times, and therefore, they they move together through 243 00:09:39.115 --> 00:09:39.615 - space. 244 00:09:41.355 --> 00:09:44.334 - So they are actually the way to, 245 00:09:45.514 --> 00:09:46.014 - discover, 246 00:09:46.714 --> 00:09:49.710 - these mergers is by looking for such groups 247 00:09:49.710 --> 00:09:52.429 - of stars that are moving together through space. 248 00:09:52.429 --> 00:09:55.389 - So that's very important because that then helps 249 00:09:55.389 --> 00:09:57.950 - us. If we find such groups of stars, 250 00:09:57.950 --> 00:10:00.049 - then we basically know such stars 251 00:10:00.509 --> 00:10:01.570 - formed together, 252 00:10:02.294 --> 00:10:05.434 - and that pinpoints to a common origin. 253 00:10:07.014 --> 00:10:09.674 - And you've all you've used a technique called 254 00:10:09.735 --> 00:10:10.235 - chemodynamics 255 00:10:11.575 --> 00:10:14.054 - to show that many stars in the Milky 256 00:10:14.054 --> 00:10:17.115 - Way were born in dwarf galaxies. 257 00:10:17.669 --> 00:10:19.370 - Can you explain this technique? 258 00:10:21.110 --> 00:10:22.230 - Yes. Indeed. So, 259 00:10:22.870 --> 00:10:23.370 - chemodynamics 260 00:10:23.909 --> 00:10:26.389 - refers to the fact that we use both 261 00:10:26.389 --> 00:10:29.929 - dynamical information, so say the motions of stars, 262 00:10:30.615 --> 00:10:34.534 - and their chemical properties, the chemical composition. So 263 00:10:34.534 --> 00:10:37.414 - the chemical composition of a star reflects the 264 00:10:37.414 --> 00:10:39.514 - environment in which they were born. 265 00:10:40.215 --> 00:10:43.115 - And so if stars are in a stream, 266 00:10:43.735 --> 00:10:46.970 - then, you can ask whether such a stream 267 00:10:46.970 --> 00:10:49.470 - was indeed formed in a dwarf galaxy. 268 00:10:50.009 --> 00:10:52.410 - And one way to testing to test that 269 00:10:52.410 --> 00:10:54.830 - is actually to look at the chemical compositions 270 00:10:54.889 --> 00:10:57.290 - of the stars because if they they were 271 00:10:57.290 --> 00:10:59.610 - born in a galaxy, they they would have 272 00:10:59.610 --> 00:11:00.110 - similar 273 00:11:00.634 --> 00:11:02.794 - DNA as it were. They will follow a 274 00:11:02.794 --> 00:11:03.615 - very characteristic 275 00:11:04.235 --> 00:11:04.735 - track 276 00:11:05.195 --> 00:11:06.654 - in chemical space. 277 00:11:07.115 --> 00:11:10.174 - So that's that's at the core of identifying, 278 00:11:12.075 --> 00:11:13.455 - the stars associated 279 00:11:13.835 --> 00:11:14.975 - to past mergers. 280 00:11:15.919 --> 00:11:18.559 - I see. And and, Per, I'd like to 281 00:11:18.559 --> 00:11:19.759 - ask you about, 282 00:11:20.240 --> 00:11:21.860 - the other two laureates, 283 00:11:23.039 --> 00:11:23.779 - this year. 284 00:11:24.799 --> 00:11:25.299 - Vasiliy 285 00:11:25.759 --> 00:11:26.259 - Belokharov 286 00:11:27.120 --> 00:11:29.620 - of The UK's University of Cambridge 287 00:11:30.365 --> 00:11:33.745 - is honored for his work on stellar streams. 288 00:11:34.365 --> 00:11:36.704 - What are his main contributions 289 00:11:37.084 --> 00:11:39.985 - to our understanding of the Milky Way? 290 00:11:40.524 --> 00:11:41.884 - Well, there are several, but, 291 00:11:42.684 --> 00:11:43.504 - I can mention, 292 00:11:44.220 --> 00:11:45.980 - first of all, his discovery of what was 293 00:11:45.980 --> 00:11:48.639 - called the field of streams where you see, 294 00:11:49.500 --> 00:11:50.399 - several streams, 295 00:11:51.419 --> 00:11:52.959 - being split up in, 296 00:11:53.899 --> 00:11:54.399 - and 297 00:11:54.700 --> 00:11:57.339 - some of these, at least those which were 298 00:11:57.339 --> 00:11:59.715 - in the original paper, mainly come from the 299 00:11:59.875 --> 00:12:02.514 - merger with the Sagittarius dwarf galaxy, which had 300 00:12:02.514 --> 00:12:05.095 - been discovered by Ibotta earlier. 301 00:12:05.955 --> 00:12:06.115 - And, 302 00:12:08.195 --> 00:12:10.535 - it's showing that these are from several, 303 00:12:10.995 --> 00:12:13.654 - rounds of the Sagittarius dwarf galaxy 304 00:12:14.079 --> 00:12:16.019 - having orbited our own galaxy 305 00:12:16.559 --> 00:12:18.720 - and and go coming through the the the 306 00:12:18.720 --> 00:12:19.860 - disc of our galaxy. 307 00:12:20.720 --> 00:12:20.959 - And, 308 00:12:21.919 --> 00:12:22.740 - he also, 309 00:12:24.480 --> 00:12:26.339 - independently of, Amina, 310 00:12:27.164 --> 00:12:27.664 - discovered, 311 00:12:28.684 --> 00:12:30.384 - what has been called the, 312 00:12:32.044 --> 00:12:32.544 - this, 313 00:12:34.605 --> 00:12:35.745 - Gaia Enceladus, 314 00:12:37.085 --> 00:12:38.304 - sausage or 315 00:12:39.085 --> 00:12:40.865 - Gaia and and so with this 316 00:12:43.029 --> 00:12:45.830 - event, which is the really last merger of 317 00:12:45.830 --> 00:12:47.850 - a big galaxy with our own galaxy, 318 00:12:48.629 --> 00:12:50.789 - some 10,000,000,000 years ago. And, 319 00:12:51.429 --> 00:12:52.649 - in in two different, 320 00:12:54.424 --> 00:12:56.845 - somewhat different ways, Amina and, 321 00:12:58.184 --> 00:12:58.684 - Vasili, 322 00:12:59.865 --> 00:13:00.845 - discovered this 323 00:13:01.225 --> 00:13:01.725 - simultaneously. 324 00:13:03.384 --> 00:13:05.804 - Yeah. I I I was intrigued by this 325 00:13:05.945 --> 00:13:06.445 - sausage. 326 00:13:07.230 --> 00:13:08.909 - I mean, maybe, Amina, could you tell us 327 00:13:08.909 --> 00:13:12.029 - a bit more about this this sausage event? 328 00:13:12.350 --> 00:13:14.450 - I mean, I'm guessing it's called a sausage 329 00:13:14.509 --> 00:13:16.529 - because it's sausage shaped. 330 00:13:16.909 --> 00:13:19.870 - Is it a sausage say shaped structure of 331 00:13:19.870 --> 00:13:20.370 - stars 332 00:13:20.830 --> 00:13:22.370 - out there in the Milky Way? 333 00:13:23.654 --> 00:13:24.855 - Yes. So so the, 334 00:13:25.654 --> 00:13:26.315 - the way, 335 00:13:27.095 --> 00:13:29.595 - the name of the sausage comes from, 336 00:13:30.535 --> 00:13:33.754 - the distribution of stars actually in their velocity 337 00:13:34.134 --> 00:13:34.470 - space. 338 00:13:35.589 --> 00:13:37.669 - So if you look at stars in the 339 00:13:37.669 --> 00:13:38.329 - solar vicinity, 340 00:13:39.990 --> 00:13:41.370 - and you plot the velocities, 341 00:13:43.029 --> 00:13:45.769 - the rotation of velocity against the velocities 342 00:13:46.309 --> 00:13:47.209 - of the oscillations 343 00:13:47.750 --> 00:13:49.750 - in the plane itself, what you see is 344 00:13:49.750 --> 00:13:51.965 - a structure that is very elongated, 345 00:13:52.585 --> 00:13:55.485 - and that's where the name sausage came from. 346 00:13:57.305 --> 00:14:00.184 - And and it reflects how actually was, 347 00:14:00.665 --> 00:14:01.165 - identified 348 00:14:01.705 --> 00:14:02.205 - by, 349 00:14:02.745 --> 00:14:03.245 - Vasili 350 00:14:03.625 --> 00:14:05.004 - in in his work. 351 00:14:06.699 --> 00:14:07.199 - Complimentary 352 00:14:07.579 --> 00:14:08.959 - to that or independently 353 00:14:09.659 --> 00:14:10.399 - of that, 354 00:14:11.419 --> 00:14:14.459 - we identified it in a different way. We 355 00:14:14.459 --> 00:14:16.860 - also looked at the kinematics of stars, but 356 00:14:16.860 --> 00:14:18.799 - as I was explaining before, 357 00:14:20.225 --> 00:14:21.524 - we looked at the chemistry, 358 00:14:23.024 --> 00:14:25.184 - of the stars. And what we found was 359 00:14:25.184 --> 00:14:29.024 - actually that stars that have peculiar kinematics, they're 360 00:14:29.024 --> 00:14:30.245 - slightly retrograde, 361 00:14:31.184 --> 00:14:32.804 - so they they go counterclockwise 362 00:14:34.529 --> 00:14:37.169 - in the opposite direction of the vast majority 363 00:14:37.169 --> 00:14:38.710 - of stars in the disk. 364 00:14:39.490 --> 00:14:41.350 - What we found is that the chemistry 365 00:14:41.809 --> 00:14:44.370 - was clearly telling us that the stars were 366 00:14:44.370 --> 00:14:46.690 - not born in the Milky Way, but were 367 00:14:46.690 --> 00:14:47.590 - born elsewhere 368 00:14:47.970 --> 00:14:48.789 - in a different 369 00:14:49.605 --> 00:14:51.144 - galaxy, in a different system. 370 00:14:52.485 --> 00:14:54.644 - So in that way, the two pictures kind 371 00:14:54.644 --> 00:14:55.125 - of, 372 00:14:56.004 --> 00:14:59.144 - came together, and the system was really identified 373 00:14:59.365 --> 00:15:01.445 - as such as and in fact, we could 374 00:15:01.445 --> 00:15:04.245 - tell when the merger happened and how it 375 00:15:04.245 --> 00:15:04.745 - happened 376 00:15:05.059 --> 00:15:05.559 - and, 377 00:15:06.419 --> 00:15:08.519 - that there was a disk at the time. 378 00:15:09.059 --> 00:15:11.779 - So very many things actually emerged for that 379 00:15:11.860 --> 00:15:13.799 - from that from those studies. 380 00:15:15.059 --> 00:15:17.059 - And I suppose the the story of the 381 00:15:17.059 --> 00:15:18.360 - Milky Way's formation 382 00:15:18.980 --> 00:15:19.959 - isn't over. 383 00:15:20.524 --> 00:15:20.965 - And, 384 00:15:21.404 --> 00:15:23.404 - I I think one of the reasons we 385 00:15:23.404 --> 00:15:24.524 - know that is, 386 00:15:25.085 --> 00:15:27.985 - thanks to the work of the third, laureate, 387 00:15:28.524 --> 00:15:29.024 - Rodrigo, 388 00:15:29.725 --> 00:15:30.225 - Ibata 389 00:15:30.845 --> 00:15:31.745 - of France's 390 00:15:32.045 --> 00:15:32.545 - University 391 00:15:32.924 --> 00:15:33.745 - of Strasbourg. 392 00:15:34.620 --> 00:15:36.379 - Per, can you can you tell us a 393 00:15:36.379 --> 00:15:38.000 - bit about his work 394 00:15:38.379 --> 00:15:38.779 - and, 395 00:15:39.259 --> 00:15:41.580 - his discovery that the Milky Way is still 396 00:15:41.580 --> 00:15:42.080 - accreting 397 00:15:42.620 --> 00:15:43.600 - dwarf galaxies? 398 00:15:45.980 --> 00:15:47.279 - Well, the early work, 399 00:15:48.139 --> 00:15:50.304 - is really all the way back to his 400 00:15:50.304 --> 00:15:53.424 - PhD thesis, I think, which, was discovered in 401 00:15:53.424 --> 00:15:54.565 - 1994, 402 00:15:55.105 --> 00:15:57.125 - of him together with Irvin and Gilmore, 403 00:15:57.825 --> 00:16:00.245 - of the Sagittarius Dwarf Galaxy, 404 00:16:00.705 --> 00:16:03.350 - which is directly on the other side of 405 00:16:03.350 --> 00:16:05.610 - our of the center of our galaxy. 406 00:16:06.949 --> 00:16:07.449 - It's, 407 00:16:08.789 --> 00:16:11.029 - he identified it, I think, through, 408 00:16:12.549 --> 00:16:14.649 - so called carbon stars. These are, 409 00:16:15.325 --> 00:16:18.205 - extremely red, the very luminous stars at the 410 00:16:18.205 --> 00:16:19.424 - end of their lives, 411 00:16:20.044 --> 00:16:21.184 - and which, 412 00:16:22.125 --> 00:16:24.544 - we're we're seeing on on through 413 00:16:25.404 --> 00:16:27.325 - the bulge of our own galaxy on the 414 00:16:27.325 --> 00:16:30.039 - other side of our galaxy, and and this 415 00:16:30.039 --> 00:16:31.500 - was identified. And 416 00:16:32.039 --> 00:16:33.019 - it's going on 417 00:16:33.320 --> 00:16:35.320 - a polar orbit and has left these, 418 00:16:35.959 --> 00:16:36.459 - several, 419 00:16:37.159 --> 00:16:38.620 - streams after it. 420 00:16:39.799 --> 00:16:40.700 - So this is 421 00:16:41.375 --> 00:16:44.355 - probably the most recent merger because it's ongoing 422 00:16:44.414 --> 00:16:44.914 - now. 423 00:16:46.894 --> 00:16:47.934 - Probably this is, 424 00:16:48.495 --> 00:16:48.995 - Sagittarius 425 00:16:49.375 --> 00:16:49.875 - dwarf 426 00:16:50.414 --> 00:16:52.735 - will finally be totally merged into our galaxy. 427 00:16:52.735 --> 00:16:53.235 - Maybe 428 00:16:53.789 --> 00:16:55.970 - a substantial part of it has already, 429 00:16:56.590 --> 00:16:58.750 - been mixed, other stars, and it has been 430 00:16:58.750 --> 00:17:01.149 - mixed into the stars of our galaxy, but 431 00:17:01.149 --> 00:17:02.289 - it's still ongoing. 432 00:17:02.669 --> 00:17:03.570 - So this was, 433 00:17:04.829 --> 00:17:05.890 - his early work. 434 00:17:06.884 --> 00:17:08.005 - What we are also very, 435 00:17:08.884 --> 00:17:10.085 - really like is his, 436 00:17:10.725 --> 00:17:12.505 - much more recent work on 437 00:17:12.805 --> 00:17:17.065 - stellar streams in the Andromedae galaxy, the nearest 438 00:17:17.285 --> 00:17:18.424 - really big galaxy, 439 00:17:19.845 --> 00:17:20.345 - from, 440 00:17:21.045 --> 00:17:21.705 - to ours, 441 00:17:22.200 --> 00:17:24.140 - a bit bigger than our own galaxy. 442 00:17:25.559 --> 00:17:27.659 - Where he has also identified similar, 443 00:17:28.279 --> 00:17:31.400 - collision events, in the in that galaxy. So 444 00:17:31.400 --> 00:17:33.960 - it's not something only happening our in our 445 00:17:33.960 --> 00:17:36.539 - own galaxy. It happens in other galaxies too. 446 00:17:37.204 --> 00:17:39.224 - I see. And and are we confident 447 00:17:39.684 --> 00:17:42.025 - that other galaxies are also 448 00:17:42.484 --> 00:17:45.625 - being built or have been built use, by 449 00:17:46.005 --> 00:17:46.505 - hierarchical 450 00:17:47.285 --> 00:17:49.204 - accretion? Is does this seem to be a 451 00:17:49.204 --> 00:17:52.585 - universal thing in in galaxy formation? 452 00:17:53.259 --> 00:17:55.900 - Well, that it's still a subject under study, 453 00:17:55.900 --> 00:17:57.200 - of course. But, 454 00:17:58.460 --> 00:17:59.200 - for example, 455 00:17:59.660 --> 00:18:01.279 - the European Space Agency 456 00:18:01.900 --> 00:18:04.779 - is now planning this is Araki's mission to 457 00:18:04.779 --> 00:18:06.375 - be launched in 2030, 458 00:18:06.615 --> 00:18:08.315 - which will look look for, 459 00:18:09.255 --> 00:18:10.555 - features in the halos, 460 00:18:11.095 --> 00:18:15.255 - dwarf galaxies and stellar streams and around 80 461 00:18:15.255 --> 00:18:16.394 - nearby galaxies. 462 00:18:17.174 --> 00:18:17.654 - So this, 463 00:18:18.214 --> 00:18:20.460 - can be interesting in the next decade. 464 00:18:22.279 --> 00:18:24.619 - And, Amina, I wanted to ask you about 465 00:18:24.680 --> 00:18:27.259 - the sort of the significance of knowing 466 00:18:27.799 --> 00:18:28.200 - that, 467 00:18:29.559 --> 00:18:30.380 - that this 468 00:18:30.840 --> 00:18:32.700 - accretion process is occurring. 469 00:18:34.234 --> 00:18:37.214 - Does this tell us something about, you know, 470 00:18:37.674 --> 00:18:40.875 - mysteries of of the universe like like dark 471 00:18:40.875 --> 00:18:41.375 - matter? 472 00:18:42.315 --> 00:18:44.654 - You know, for example, does, hierarchical 473 00:18:45.674 --> 00:18:46.174 - accretion, 474 00:18:47.230 --> 00:18:49.950 - does it sort of agree with the idea 475 00:18:49.950 --> 00:18:50.269 - that, 476 00:18:50.909 --> 00:18:52.369 - the universe is permeated 477 00:18:52.909 --> 00:18:55.309 - by dark matter and that dark matter is 478 00:18:55.309 --> 00:18:55.809 - involved 479 00:18:56.190 --> 00:18:58.750 - in this accretion process? Does it tell us 480 00:18:58.750 --> 00:18:59.890 - something about that? 481 00:19:01.424 --> 00:19:03.585 - Yeah. I guess there are multiple ways in 482 00:19:03.585 --> 00:19:05.365 - which it tells us about, 483 00:19:06.144 --> 00:19:08.304 - dark matter. One of the things is, of 484 00:19:08.304 --> 00:19:09.204 - course, if, 485 00:19:10.304 --> 00:19:12.785 - you know, the lambda called dark matter model 486 00:19:12.785 --> 00:19:14.244 - is correct, the mergers 487 00:19:14.769 --> 00:19:17.170 - must have been important in the history of 488 00:19:17.170 --> 00:19:20.049 - galaxies. So finding the mergers is a first 489 00:19:20.049 --> 00:19:20.549 - step. 490 00:19:20.929 --> 00:19:23.329 - Right? And so this and and what we're 491 00:19:23.329 --> 00:19:25.910 - finding for the Milky Way is indeed consistent 492 00:19:26.130 --> 00:19:27.190 - with the expectations 493 00:19:27.730 --> 00:19:28.789 - of this cosmological 494 00:19:29.329 --> 00:19:30.549 - model of hierarchical 495 00:19:31.065 --> 00:19:31.565 - merging. 496 00:19:32.904 --> 00:19:34.845 - On the other hand, these streams, 497 00:19:35.144 --> 00:19:38.505 - because they are composed of stars on very, 498 00:19:38.904 --> 00:19:41.404 - similar orbits, they're very sensitive 499 00:19:41.704 --> 00:19:44.125 - to actually the nature of dark matter. 500 00:19:44.640 --> 00:19:47.039 - The cold dark matter model predicts that the 501 00:19:47.039 --> 00:19:48.259 - halos of galaxies 502 00:19:48.799 --> 00:19:49.299 - have 503 00:19:49.840 --> 00:19:50.340 - tiny, 504 00:19:51.200 --> 00:19:51.700 - substructures 505 00:19:52.240 --> 00:19:54.740 - in them in the form of dark satellites, 506 00:19:55.119 --> 00:19:56.019 - dark subhalos. 507 00:19:56.724 --> 00:19:59.845 - And if these dark subhalos come close to 508 00:19:59.845 --> 00:20:00.904 - stellar streams, 509 00:20:01.444 --> 00:20:02.984 - then they cause a perturbation. 510 00:20:03.365 --> 00:20:05.764 - It is as if these streams are moving 511 00:20:05.764 --> 00:20:08.484 - in a on on a bumpy road as 512 00:20:08.484 --> 00:20:10.724 - it were, and you would see the bumps 513 00:20:10.724 --> 00:20:11.490 - if such, 514 00:20:12.369 --> 00:20:14.630 - collisions or encounters would happen. 515 00:20:15.089 --> 00:20:17.569 - So stellar streams are also useful in this 516 00:20:17.569 --> 00:20:19.910 - context, and what people are finding 517 00:20:20.450 --> 00:20:22.529 - at the moment is that very many of 518 00:20:22.529 --> 00:20:23.190 - the streams 519 00:20:23.664 --> 00:20:25.684 - actually show signs of perturbations, 520 00:20:26.144 --> 00:20:27.684 - which is very interesting, 521 00:20:28.384 --> 00:20:31.265 - except that for at the moment, it's hard 522 00:20:31.265 --> 00:20:32.005 - to disentangle 523 00:20:32.464 --> 00:20:34.484 - what are the sources of the perturbations. 524 00:20:34.785 --> 00:20:37.664 - So we're really working out what other ways, 525 00:20:38.970 --> 00:20:39.789 - could be, 526 00:20:40.650 --> 00:20:41.950 - could actually cause, 527 00:20:42.329 --> 00:20:44.410 - the the the features that we see in 528 00:20:44.410 --> 00:20:46.890 - the streams. It might be these dark matter 529 00:20:46.890 --> 00:20:49.230 - subhalos, but we're not certain yet. 530 00:20:50.329 --> 00:20:52.190 - I see. And and so 531 00:20:53.134 --> 00:20:54.674 - so when you look at a galaxy 532 00:20:54.974 --> 00:20:56.755 - or at the Milky Way, 533 00:20:57.375 --> 00:20:57.875 - your 534 00:20:59.214 --> 00:21:00.515 - I suppose your interpretation 535 00:21:01.375 --> 00:21:03.794 - of the structure would would lean towards, 536 00:21:05.375 --> 00:21:08.109 - cold dark matter rather than, you know, for 537 00:21:08.109 --> 00:21:10.769 - example, the theory of modified gravity, 538 00:21:11.309 --> 00:21:12.130 - like MOND, 539 00:21:13.069 --> 00:21:13.730 - the hierarchical 540 00:21:14.909 --> 00:21:15.409 - accretion. 541 00:21:16.429 --> 00:21:18.990 - Should it be interpreted as, well proof is 542 00:21:18.990 --> 00:21:21.934 - probably a strong word for dark matter rather 543 00:21:21.934 --> 00:21:23.475 - than evidence for, 544 00:21:24.494 --> 00:21:26.494 - MOND? Or or are the things that you're 545 00:21:26.494 --> 00:21:27.535 - looking at maybe too 546 00:21:28.174 --> 00:21:30.734 - or the or the the the length scales 547 00:21:30.734 --> 00:21:33.154 - too small to really tell you anything about 548 00:21:33.535 --> 00:21:34.674 - something like MOND? 549 00:21:36.130 --> 00:21:38.309 - So so in fact, I think MOND, 550 00:21:38.849 --> 00:21:42.470 - can be tested. We've also tested our, MOND 551 00:21:42.529 --> 00:21:44.309 - using stellar streams, 552 00:21:44.930 --> 00:21:47.250 - and we find we find it's not a 553 00:21:47.250 --> 00:21:48.309 - very good description 554 00:21:48.690 --> 00:21:51.565 - actually of the motions of stars in stellar 555 00:21:51.565 --> 00:21:52.065 - streams. 556 00:21:52.524 --> 00:21:54.684 - But that doesn't rule out that there may 557 00:21:54.684 --> 00:21:58.924 - be other theories, alternative theories of gravity that 558 00:21:58.924 --> 00:22:01.804 - could explain what we see around us. I 559 00:22:01.804 --> 00:22:02.304 - think 560 00:22:02.759 --> 00:22:05.960 - if we have an alternative model, it probably 561 00:22:05.960 --> 00:22:08.700 - will be very close to the Lambda CDM 562 00:22:08.759 --> 00:22:09.900 - model because, 563 00:22:10.759 --> 00:22:13.080 - you know, the it works. It seems to 564 00:22:13.240 --> 00:22:15.559 - it's not proof, like you say, because that's 565 00:22:15.559 --> 00:22:18.265 - too strong, but, certainly, there is consistency 566 00:22:18.644 --> 00:22:20.105 - as far as we can tell. 567 00:22:21.285 --> 00:22:21.785 - And, 568 00:22:22.964 --> 00:22:25.865 - there must be lots that we don't know 569 00:22:26.244 --> 00:22:27.704 - about the Milky Way. 570 00:22:30.029 --> 00:22:30.529 - Amina, 571 00:22:31.230 --> 00:22:33.549 - what's the big mystery for you? What's the 572 00:22:33.549 --> 00:22:35.410 - mystery that you would like to solve, 573 00:22:36.670 --> 00:22:38.930 - you know, if if you had the chance? 574 00:22:40.029 --> 00:22:41.970 - I guess there are quite a few mysteries. 575 00:22:42.454 --> 00:22:44.134 - I think I I can think of a 576 00:22:44.134 --> 00:22:46.695 - couple. One is indeed the nature of dark 577 00:22:46.695 --> 00:22:50.154 - matter. Right? So using streams to really constrain 578 00:22:50.375 --> 00:22:50.875 - if, 579 00:22:51.575 --> 00:22:54.474 - establish if there are these dark matter clumps 580 00:22:54.695 --> 00:22:56.875 - orbiting in the halo of our galaxy. 581 00:22:57.480 --> 00:22:59.500 - That is one really big question. 582 00:23:00.519 --> 00:23:03.000 - But also going further back in time, we've 583 00:23:03.000 --> 00:23:03.740 - been discussing, 584 00:23:04.119 --> 00:23:06.440 - you know, the last merger that we know 585 00:23:06.440 --> 00:23:09.339 - of, last big merger ten billion years ago. 586 00:23:09.734 --> 00:23:13.174 - What happened before that? And that's actually rather 587 00:23:13.174 --> 00:23:13.674 - hard, 588 00:23:15.255 --> 00:23:16.634 - to figure out because 589 00:23:17.095 --> 00:23:19.335 - at the early epochs, the universe was a 590 00:23:19.335 --> 00:23:21.355 - lot denser, so mergers 591 00:23:21.750 --> 00:23:24.230 - were happening a lot more often. And then 592 00:23:24.230 --> 00:23:26.809 - you also get mergers of similar object 593 00:23:27.430 --> 00:23:29.690 - in terms of their sizes or masses. 594 00:23:30.230 --> 00:23:31.930 - So it becomes all rather, 595 00:23:32.869 --> 00:23:34.170 - difficult to disentangle. 596 00:23:34.549 --> 00:23:35.369 - But I think 597 00:23:35.845 --> 00:23:36.664 - with the new, 598 00:23:37.045 --> 00:23:38.424 - Gaia data releases, 599 00:23:40.005 --> 00:23:43.225 - and also with new surveys giving us chemistry, 600 00:23:43.365 --> 00:23:45.785 - I'm hopeful that we can push the boundary 601 00:23:45.845 --> 00:23:47.625 - much further back in time. 602 00:23:48.910 --> 00:23:50.829 - And and we've been talking about, I suppose, 603 00:23:50.829 --> 00:23:52.369 - the history or the archaeology 604 00:23:53.069 --> 00:23:54.450 - of the Milky Way. 605 00:23:55.230 --> 00:23:56.289 - What what does 606 00:23:56.670 --> 00:23:59.069 - your research and the research of your of 607 00:23:59.069 --> 00:24:02.045 - your colleagues, the other laureates, what does it 608 00:24:02.045 --> 00:24:04.365 - tell us about the fate of the Milky 609 00:24:04.365 --> 00:24:05.804 - Way? I mean, do you think is it 610 00:24:05.804 --> 00:24:07.184 - gonna keep going 611 00:24:07.724 --> 00:24:08.785 - on accreting 612 00:24:09.404 --> 00:24:12.045 - dwarf galaxies, or has it hoovered up all 613 00:24:12.045 --> 00:24:14.144 - the dwarf galaxies that are available? 614 00:24:14.609 --> 00:24:16.390 - And, you know, it's it it'll 615 00:24:16.849 --> 00:24:19.589 - go into a different phase of its existence, 616 00:24:19.650 --> 00:24:21.029 - or maybe it's in that 617 00:24:21.730 --> 00:24:24.130 - sort of steady phase at the moment. What 618 00:24:24.130 --> 00:24:26.690 - what what's going to happen to the Milky 619 00:24:26.690 --> 00:24:27.190 - Way? 620 00:24:28.595 --> 00:24:30.615 - So as as Per was saying, 621 00:24:31.634 --> 00:24:33.894 - it's currently eating up Sagittarius. 622 00:24:34.595 --> 00:24:36.595 - Right? So I think it will be one 623 00:24:36.595 --> 00:24:38.994 - more passage of the dwarf and it will 624 00:24:38.994 --> 00:24:41.494 - be gone. It will be completely dissolved. 625 00:24:43.100 --> 00:24:46.059 - What we're seeing is it's actually interacting with 626 00:24:46.059 --> 00:24:47.840 - the large and small Magellanic 627 00:24:48.220 --> 00:24:48.720 - clouds. 628 00:24:49.100 --> 00:24:51.740 - And these are more massive, so that also 629 00:24:51.740 --> 00:24:54.140 - leaves an imprint on the on the Milky 630 00:24:54.140 --> 00:24:56.380 - Way. We can actually see a response of 631 00:24:56.380 --> 00:24:58.075 - the Milky Way to their present 632 00:24:58.875 --> 00:24:59.375 - presence. 633 00:24:59.674 --> 00:25:01.615 - So that is, the next 634 00:25:02.075 --> 00:25:02.575 - merger. 635 00:25:04.075 --> 00:25:06.015 - And then in the in the future, 636 00:25:07.115 --> 00:25:08.654 - what we see is also, 637 00:25:09.859 --> 00:25:12.580 - you know, our neighbor that also Rodrigo Ibotta 638 00:25:12.580 --> 00:25:15.720 - has studied, the m 31 galaxy, the Andromeda 639 00:25:15.859 --> 00:25:16.359 - galaxy. 640 00:25:16.740 --> 00:25:18.980 - And it's very likely that the Milky Way 641 00:25:18.980 --> 00:25:22.119 - and Andromeda will actually merge in the future. 642 00:25:23.644 --> 00:25:25.664 - But the sky will look rather different, 643 00:25:26.444 --> 00:25:28.704 - at the time because the moment you merge 644 00:25:28.765 --> 00:25:31.884 - two systems of similar size, the discs are 645 00:25:31.884 --> 00:25:32.704 - very perturbed, 646 00:25:33.404 --> 00:25:35.579 - and so we may end up in an 647 00:25:35.579 --> 00:25:38.059 - elliptical galaxy. But, you know, it's a long 648 00:25:38.059 --> 00:25:39.519 - way down the road. 649 00:25:40.140 --> 00:25:42.460 - I see. Okay. And and what about you, 650 00:25:42.460 --> 00:25:43.259 - Per? What's, 651 00:25:43.660 --> 00:25:45.259 - I mean, what would you like to see 652 00:25:45.259 --> 00:25:47.279 - in terms of Milky Way 653 00:25:47.794 --> 00:25:50.595 - research or, you know, research on galaxies in 654 00:25:50.595 --> 00:25:52.994 - general? What what what what's your wish list? 655 00:25:52.994 --> 00:25:54.375 - What would you like to see 656 00:25:54.835 --> 00:25:56.454 - happen in the future of research? 657 00:25:57.875 --> 00:25:58.934 - Well, as a cosmologist, 658 00:25:59.394 --> 00:26:01.654 - I'm most intrigued really by, 659 00:26:04.230 --> 00:26:06.309 - the the work which Amina and her colleagues 660 00:26:06.309 --> 00:26:06.890 - are doing, 661 00:26:07.589 --> 00:26:09.349 - on what what it can say about the 662 00:26:09.349 --> 00:26:12.009 - nature of the dark matter. That is really, 663 00:26:14.079 --> 00:26:14.579 - because 664 00:26:15.394 --> 00:26:17.654 - there have been a number of of 665 00:26:18.274 --> 00:26:21.174 - problems with the Lambda CDM model, which 666 00:26:21.714 --> 00:26:24.115 - grew up in the nineteen nineties and really 667 00:26:24.115 --> 00:26:24.615 - was 668 00:26:25.075 --> 00:26:26.774 - and so is, 669 00:26:27.394 --> 00:26:29.335 - to from the late nineteen nineties, 670 00:26:29.634 --> 00:26:30.420 - have been the 671 00:26:30.900 --> 00:26:31.940 - really leading theory. 672 00:26:32.980 --> 00:26:34.980 - And I want to see that dead in 673 00:26:34.980 --> 00:26:37.619 - some way, because it's been with us for 674 00:26:37.619 --> 00:26:38.519 - so long now. 675 00:26:38.820 --> 00:26:41.640 - No. It it gives a very, very good 676 00:26:41.859 --> 00:26:43.080 - description of, 677 00:26:43.859 --> 00:26:44.680 - of our observations, 678 00:26:45.845 --> 00:26:48.565 - but I would hope to find something fishy 679 00:26:48.565 --> 00:26:49.605 - there. And, 680 00:26:50.565 --> 00:26:52.565 - what has been looked upon as a problem 681 00:26:52.565 --> 00:26:53.625 - was what, Amina 682 00:26:54.085 --> 00:26:54.724 - mentioned that, 683 00:26:55.525 --> 00:26:58.259 - the the the theory predicts 684 00:26:58.740 --> 00:27:01.000 - very many more dwarf galaxies 685 00:27:01.299 --> 00:27:03.700 - than we see. And the way out of 686 00:27:03.700 --> 00:27:05.539 - that is to say that, well, they are 687 00:27:05.539 --> 00:27:07.539 - there in dark matter, but they are not 688 00:27:07.539 --> 00:27:09.619 - there in stars. They they they don't have 689 00:27:09.619 --> 00:27:10.119 - stars. 690 00:27:11.515 --> 00:27:12.015 - And, 691 00:27:12.835 --> 00:27:16.075 - if, I mean, I've, said we can study 692 00:27:16.075 --> 00:27:18.894 - this further in the by the stellar streams. 693 00:27:18.954 --> 00:27:21.134 - That is something I'm looking forward to see. 694 00:27:22.634 --> 00:27:24.634 - Well, that's great. I mean, it sounds like, 695 00:27:24.794 --> 00:27:27.769 - there's lots more to know about the Milky 696 00:27:27.769 --> 00:27:28.269 - Way. 697 00:27:28.970 --> 00:27:29.950 - Amina, congratulations 698 00:27:30.329 --> 00:27:30.829 - again 699 00:27:31.369 --> 00:27:31.849 - on, 700 00:27:32.570 --> 00:27:34.750 - winning or sharing this year's, 701 00:27:35.289 --> 00:27:37.309 - Kavli Prize in astrophysics. 702 00:27:37.849 --> 00:27:41.505 - And, Per, thank you, and to Amina for 703 00:27:41.505 --> 00:27:42.644 - coming on the podcast. 704 00:27:43.184 --> 00:27:43.924 - Thank you. 705 00:27:44.464 --> 00:27:45.204 - Thank you. 706 00:27:53.130 --> 00:27:54.430 - That was the astronomer 707 00:27:54.809 --> 00:27:55.869 - Amina Helmi 708 00:27:56.170 --> 00:27:58.589 - who shares the 2026 709 00:27:58.970 --> 00:28:00.829 - Kavli Prize in Astrophysics 710 00:28:01.450 --> 00:28:02.349 - with Vasili 711 00:28:02.650 --> 00:28:03.150 - Balakarov 712 00:28:03.769 --> 00:28:04.750 - and Rodrigo 713 00:28:05.210 --> 00:28:05.710 - Ibadah. 714 00:28:06.494 --> 00:28:09.695 - We were joined by Per Barth Lilia, who 715 00:28:09.695 --> 00:28:12.355 - is chair of the twenty twenty six 716 00:28:12.654 --> 00:28:15.394 - Kavli Prize Committee in Astrophysics. 717 00:28:16.654 --> 00:28:17.154 - Congratulations 718 00:28:17.535 --> 00:28:20.015 - to Amina, and thanks to both of my 719 00:28:20.015 --> 00:28:23.440 - guests for their insights into the Milky Way. 720 00:28:24.220 --> 00:28:27.200 - This episode is sponsored by the Kavli Prize, 721 00:28:27.500 --> 00:28:31.039 - which honors scientists for breakthroughs in astrophysics, 722 00:28:31.819 --> 00:28:32.319 - nanoscience, 723 00:28:32.779 --> 00:28:33.599 - and neuroscience, 724 00:28:34.664 --> 00:28:38.205 - transforming our understanding of the big, the small, 725 00:28:38.265 --> 00:28:39.244 - and the complex. 726 00:28:39.945 --> 00:28:42.664 - The vision for the Kavli Prize comes from 727 00:28:42.664 --> 00:28:44.525 - Fred Kavli, a Norwegian 728 00:28:44.904 --> 00:28:45.404 - American 729 00:28:45.705 --> 00:28:46.205 - entrepreneur 730 00:28:46.759 --> 00:28:47.419 - and philanthropist 731 00:28:47.960 --> 00:28:49.339 - who turned his lifelong 732 00:28:49.799 --> 00:28:51.179 - fascination with science 733 00:28:51.480 --> 00:28:53.980 - into a lasting legacy for recognizing 734 00:28:54.519 --> 00:28:55.659 - scientific breakthroughs 735 00:28:55.960 --> 00:28:58.379 - and for supporting basic research. 736 00:28:59.164 --> 00:29:01.164 - I'm afraid that's all the time we have 737 00:29:01.164 --> 00:29:02.464 - for this week's podcast. 738 00:29:02.845 --> 00:29:05.964 - I'm Hamish Johnston, and our producer is Fred 739 00:29:05.964 --> 00:29:06.464 - Iles. 740 00:29:06.924 --> 00:29:09.884 - The music in this episode was composed and 741 00:29:09.884 --> 00:29:10.384 - performed 742 00:29:10.765 --> 00:29:11.585 - by the physicist 743 00:29:12.125 --> 00:29:13.025 - Philip Moriarty, 744 00:29:13.565 --> 00:29:14.625 - and it's called 745 00:29:15.099 --> 00:29:16.799 - one three seven. 746 00:29:17.339 --> 00:29:19.200 - We'll be back again next week.