# ‘Galactic archaeologists’ share the 2026 Kavli Prize in Astrophysics

An episode of [Physics World Weekly Podcast](https://invisiblenetwork.ai/podcast/1400686733), 11 Jun 2026, 30 min.

Audio: https://media.blubrry.com/physicsworldweeklypodcast/content.blubrry.com/physicsworldweeklypodcast/PWWeekly11June2026KavliPrize.mp3

Laureate Amina Helmi and Per Barth Lilje of the prize committee are our guests

## Transcript

[0:07] - Hello, and welcome to this episode of the
[0:10] - Physics World Weekly Podcast,
[0:12] - which is sponsored by the Kavli Prize.
[0:15] - The Kavli Prize honors scientists for breakthroughs
[0:19] - in astrophysics,
[0:21] - nanoscience,
[0:22] - and neuroscience,
[0:24] - transforming our understanding of the big, the small,
[0:27] - and the complex.
[0:29] - The vision for the Kavli Prize comes from
[0:32] - Fred Kavli, a Norwegian American entrepreneur
[0:36] - and philanthropist
[0:38] - who turned his lifelong
[0:40] - fascination with science
[0:41] - into a lasting legacy for recognizing
[0:45] - scientific breakthroughs and for supporting basic research.
[0:49] - The 2026
[0:51] - Kavli Prize in Astrophysics
[0:54] - was announced on June 10. And I'm very
[0:57] - pleased to be joined by the astronomer
[1:00] - Amina Helmi,
[1:02] - who shares this year's prize with Vasily
[1:05] - Bolakarov
[1:06] - and Rodrigo
[1:08] - Ibadah.
[1:09] - She joins me down the line from the
[1:11] - Kapteine Astronomical
[1:13] - Institute
[1:14] - in The Netherlands,
[1:15] - where she is professor of astronomy.
[1:19] - I would also like to welcome
[1:21] - Per Barth Lilia
[1:23] - to the podcast.
[1:24] - He is chair of the twenty twenty six
[1:27] - Kavli Prize Committee in Astrophysics
[1:30] - and speaks to us from the Institute of
[1:33] - Theoretical
[1:34] - Astrophysics
[1:35] - at Norway's
[1:36] - University of Oslo,
[1:38] - where he is professor of cosmology.
[1:41] - Amina and Per,
[1:43] - welcome to the podcast,
[1:45] - and congratulations,
[1:46] - Amina, for sharing the 2026
[1:49] - Kavli Prize in Astrophysics.
[1:52] - Thank you, Hamish.
[1:54] - Thank you for,
[1:56] - inviting me,
[1:58] - and thank you also to Per for selecting
[2:02] - us to be the winners of this year
[2:04] - for being the chair of the committee.
[2:08] - It's an enormous pleasure and an honor to
[2:10] - be here today.
[2:12] - And, Per, before we chat about Amina's work
[2:15] - and that of her fellow laureates,
[2:18] - can you give us a citation
[2:20] - for this year's prize
[2:21] - and perhaps provide a little insight into why
[2:24] - the committee
[2:25] - came to its decision?
[2:28] - Well, the citation,
[2:30] - for for the award is that it it's
[2:32] - given for uncovering the fossil evidence of past
[2:35] - mergers
[2:36] - proving that the Milky Way galaxy was built
[2:38] - through hierarchical accretion.
[2:40] - The three Kavli Prize laureates have fundamentally transformed
[2:44] - our understanding
[2:45] - of how massive galaxies
[2:47] - have evolved over the history of the universe.
[2:49] - In the hierarchical framework of galaxy formation,
[2:52] - massive galaxies are thought to grow by accreting
[2:55] - numerous smaller galactic systems
[2:58] - from their surrounding circumgalactic
[3:00] - environment.
[3:01] - The laureates have provided clear observational evidence
[3:05] - that major
[3:06] - merger events have indeed occurred, that their signatures
[3:09] - remain visible years later in our Milky Way
[3:12] - galaxy.
[3:13] - The committee,
[3:15] - has received quite a number of nominations
[3:18] - in all different fields covering
[3:21] - space science and astronomy,
[3:23] - astrophysics,
[3:24] - instrument
[3:26] - instrumentation.
[3:27] - And,
[3:28] - we had a tough job, of course,
[3:30] - which, the committee always has of,
[3:33] - narrowing down who we wanted to,
[3:37] - to give the, to give the price to
[3:39] - this year. But we found that,
[3:43] - this is really fundamental work. It's also done
[3:46] - by,
[3:47] - quite young scientists who are still in their
[3:50] - most active,
[3:52] - period their career. And we thought this would
[3:55] - be a very good,
[3:57] - signal to them and to this community. And,
[4:00] - also,
[4:01] - in addition to that, really,
[4:03] - a signal showing how important, especially the Gaia
[4:06] - space mission is, and that it's important to
[4:10] - really
[4:11] - we also would like to
[4:13] - show that this it's important to fund this
[4:15] - until the final data releases,
[4:18] - hope to come in 2030.
[4:21] - And, Amina, can you set the scene for
[4:24] - our listeners?
[4:25] - Can you give us an overview of the
[4:27] - Milky Way?
[4:28] - What shape is it? How big is it?
[4:30] - And how many stars does it contain?
[4:33] - And and how old is it? Can can
[4:35] - you give us a potted history of the
[4:37] - Milky Way?
[4:39] - Yes. Of course. So the Milky Way is,
[4:42] - as we all know, is the galaxy that
[4:44] - we live in.
[4:46] - It's about 90,000
[4:48] - light years in diameter.
[4:50] - It has about a 100,000,000,000
[4:53] - suns or stars.
[4:55] - And and it is a typical galaxy. That's
[4:58] - so that's quite interesting.
[5:00] - It's a disk galaxy.
[5:03] - The stars in the days the majority of
[5:06] - these have formed in the last,
[5:08] - about ten billion years,
[5:12] - and it's still forming stars at about the
[5:14] - rate of a few suns per year.
[5:18] - So because it's it's a typical galaxy, it
[5:20] - also gives us the the,
[5:23] - the possibility of trying to understand how galaxy
[5:26] - formation in general works.
[5:28] - But the truth is it's our home in
[5:30] - the universe, so that makes it also extra
[5:32] - interesting.
[5:35] - And and is it I mean, I would
[5:37] - assume that because we're in the Milky Way,
[5:40] - it's it's easy for us to study. But
[5:43] - but but is that the case? I mean,
[5:45] - you know, for example, we can't stand back
[5:47] - from the Milky Way
[5:49] - and and look at it from a distance
[5:52] - and sort of see it whole.
[5:54] - On the other hand, you know, it's it's
[5:56] - very all stars are very close to us.
[5:59] - So are there pros and cons in in
[6:02] - studying the Milky Way?
[6:05] - Yes. You're absolutely right. So one of the
[6:07] - things we're still struggling, for example, is to
[6:10] - understand how many spiral arms the Milky Way
[6:13] - has because they are in the disk, and
[6:15] - we're also in the disk. So we cannot
[6:17] - raise above
[6:19] - the plane and look at it from the
[6:20] - outside.
[6:22] - But like you say,
[6:23] - because we have access to,
[6:27] - information about the individual stars, we can measure
[6:29] - the properties, we can measure how fast they
[6:32] - move, where they are located in space,
[6:35] - We can measure ages and chemical compositions.
[6:38] - All of that information is really only available
[6:42] - at the moment for stars in our galaxy.
[6:44] - And so that is what allows us to
[6:46] - reconstruct the history in so much detail.
[6:51] - And, Per, you mentioned that this year's laureates,
[6:54] - have done,
[6:56] - some really, really good work on,
[7:00] - the hierarchical
[7:01] - accretion,
[7:03] - and how the Milky Way was formed
[7:05] - by this process. Can can you give us
[7:07] - a little more insight
[7:09] - into hierarchical
[7:11] - accretion?
[7:12] - How does it happen, and and why is
[7:14] - it important
[7:15] - that we understand the Milky Way was was
[7:18] - made
[7:19] - by that process.
[7:21] - Well, from the,
[7:22] - nineteen eighties, early nineteen eighties,
[7:26] - hierarchical,
[7:27] - accretion,
[7:28] - has been
[7:29] - the common theory. But,
[7:31] - that small structures form first in the universe
[7:34] - just because
[7:36] - fluctuations
[7:36] - on that scale,
[7:38] - in the density field, which
[7:40] - finally became galaxies,
[7:42] - stars, everything,
[7:44] - was stronger on the small scales than on
[7:47] - large scales. And then these merged. But we
[7:50] - haven't really seen,
[7:52] - this working in,
[7:54] - this happening in in,
[7:56] - real time. But now,
[7:58] - Amina and her colleagues, they are showing us
[8:02] - that we really see the remnants of recent
[8:05] - and ongoing such merger events now.
[8:09] - Thanks, Per. So, Amina, much of your research
[8:12] - has focused on stellar streams.
[8:15] - And I think there's actually a stellar stream
[8:18] - named after you.
[8:19] - So what is a stellar stream,
[8:22] - and why do they support the idea of
[8:25] - hierarchical
[8:26] - accretion?
[8:29] - Yes. So, indeed, there's a stream named after
[8:32] - me.
[8:34] - So so as Pero was saying, we think
[8:37] - that galaxies or we thought, from the this
[8:40] - model from the eighties that galaxies
[8:43] - must have experienced mergers
[8:46] - as they grew in mass, particularly
[8:48] - at early times.
[8:50] - And as a galaxy orbits another galaxy,
[8:55] - it loses it feels the tidal forces of
[8:58] - the bigger system, and
[9:00] - that leads to the formation of stellar streams.
[9:03] - So these are groups of stars that have
[9:06] - lost their parent system,
[9:08] - and that actually can remain coherent
[9:11] - for even,
[9:12] - the age of the universe and longer.
[9:15] - So these are basically
[9:17] - if you would,
[9:19] - make a map of the sky, you will
[9:21] - see,
[9:23] - streams of stars, so groups of stars on
[9:25] - very coherent structures.
[9:29] - And these groups of stars also share similar
[9:32] - motions because they are all lost at similar
[9:35] - times, and therefore, they they move together through
[9:39] - space.
[9:41] - So they are actually the way to,
[9:45] - discover,
[9:46] - these mergers is by looking for such groups
[9:49] - of stars that are moving together through space.
[9:52] - So that's very important because that then helps
[9:55] - us. If we find such groups of stars,
[9:57] - then we basically know such stars
[10:00] - formed together,
[10:02] - and that pinpoints to a common origin.
[10:07] - And you've all you've used a technique called
[10:09] - chemodynamics
[10:11] - to show that many stars in the Milky
[10:14] - Way were born in dwarf galaxies.
[10:17] - Can you explain this technique?
[10:21] - Yes. Indeed. So,
[10:22] - chemodynamics
[10:23] - refers to the fact that we use both
[10:26] - dynamical information, so say the motions of stars,
[10:30] - and their chemical properties, the chemical composition. So
[10:34] - the chemical composition of a star reflects the
[10:37] - environment in which they were born.
[10:40] - And so if stars are in a stream,
[10:43] - then, you can ask whether such a stream
[10:46] - was indeed formed in a dwarf galaxy.
[10:50] - And one way to testing to test that
[10:52] - is actually to look at the chemical compositions
[10:54] - of the stars because if they they were
[10:57] - born in a galaxy, they they would have
[10:59] - similar
[11:00] - DNA as it were. They will follow a
[11:02] - very characteristic
[11:04] - track
[11:05] - in chemical space.
[11:07] - So that's that's at the core of identifying,
[11:12] - the stars associated
[11:13] - to past mergers.
[11:15] - I see. And and, Per, I'd like to
[11:18] - ask you about,
[11:20] - the other two laureates,
[11:23] - this year.
[11:24] - Vasiliy
[11:25] - Belokharov
[11:27] - of The UK's University of Cambridge
[11:30] - is honored for his work on stellar streams.
[11:34] - What are his main contributions
[11:37] - to our understanding of the Milky Way?
[11:40] - Well, there are several, but,
[11:42] - I can mention,
[11:44] - first of all, his discovery of what was
[11:45] - called the field of streams where you see,
[11:49] - several streams,
[11:51] - being split up in,
[11:53] - and
[11:54] - some of these, at least those which were
[11:57] - in the original paper, mainly come from the
[11:59] - merger with the Sagittarius dwarf galaxy, which had
[12:02] - been discovered by Ibotta earlier.
[12:05] - And,
[12:08] - it's showing that these are from several,
[12:10] - rounds of the Sagittarius dwarf galaxy
[12:14] - having orbited our own galaxy
[12:16] - and and go coming through the the the
[12:18] - disc of our galaxy.
[12:20] - And,
[12:21] - he also,
[12:24] - independently of, Amina,
[12:27] - discovered,
[12:28] - what has been called the,
[12:32] - this,
[12:34] - Gaia Enceladus,
[12:37] - sausage or
[12:39] - Gaia and and so with this
[12:43] - event, which is the really last merger of
[12:45] - a big galaxy with our own galaxy,
[12:48] - some 10,000,000,000 years ago. And,
[12:51] - in in two different,
[12:54] - somewhat different ways, Amina and,
[12:58] - Vasili,
[12:59] - discovered this
[13:01] - simultaneously.
[13:03] - Yeah. I I I was intrigued by this
[13:05] - sausage.
[13:07] - I mean, maybe, Amina, could you tell us
[13:08] - a bit more about this this sausage event?
[13:12] - I mean, I'm guessing it's called a sausage
[13:14] - because it's sausage shaped.
[13:16] - Is it a sausage say shaped structure of
[13:19] - stars
[13:20] - out there in the Milky Way?
[13:23] - Yes. So so the,
[13:25] - the way,
[13:27] - the name of the sausage comes from,
[13:30] - the distribution of stars actually in their velocity
[13:34] - space.
[13:35] - So if you look at stars in the
[13:37] - solar vicinity,
[13:39] - and you plot the velocities,
[13:43] - the rotation of velocity against the velocities
[13:46] - of the oscillations
[13:47] - in the plane itself, what you see is
[13:49] - a structure that is very elongated,
[13:52] - and that's where the name sausage came from.
[13:57] - And and it reflects how actually was,
[14:00] - identified
[14:01] - by,
[14:02] - Vasili
[14:03] - in in his work.
[14:06] - Complimentary
[14:07] - to that or independently
[14:09] - of that,
[14:11] - we identified it in a different way. We
[14:14] - also looked at the kinematics of stars, but
[14:16] - as I was explaining before,
[14:20] - we looked at the chemistry,
[14:23] - of the stars. And what we found was
[14:25] - actually that stars that have peculiar kinematics, they're
[14:29] - slightly retrograde,
[14:31] - so they they go counterclockwise
[14:34] - in the opposite direction of the vast majority
[14:37] - of stars in the disk.
[14:39] - What we found is that the chemistry
[14:41] - was clearly telling us that the stars were
[14:44] - not born in the Milky Way, but were
[14:46] - born elsewhere
[14:47] - in a different
[14:49] - galaxy, in a different system.
[14:52] - So in that way, the two pictures kind
[14:54] - of,
[14:56] - came together, and the system was really identified
[14:59] - as such as and in fact, we could
[15:01] - tell when the merger happened and how it
[15:04] - happened
[15:05] - and,
[15:06] - that there was a disk at the time.
[15:09] - So very many things actually emerged for that
[15:11] - from that from those studies.
[15:15] - And I suppose the the story of the
[15:17] - Milky Way's formation
[15:18] - isn't over.
[15:20] - And,
[15:21] - I I think one of the reasons we
[15:23] - know that is,
[15:25] - thanks to the work of the third, laureate,
[15:28] - Rodrigo,
[15:29] - Ibata
[15:30] - of France's
[15:32] - University
[15:32] - of Strasbourg.
[15:34] - Per, can you can you tell us a
[15:36] - bit about his work
[15:38] - and,
[15:39] - his discovery that the Milky Way is still
[15:41] - accreting
[15:42] - dwarf galaxies?
[15:45] - Well, the early work,
[15:48] - is really all the way back to his
[15:50] - PhD thesis, I think, which, was discovered in
[15:53] - 1994,
[15:55] - of him together with Irvin and Gilmore,
[15:57] - of the Sagittarius Dwarf Galaxy,
[16:00] - which is directly on the other side of
[16:03] - our of the center of our galaxy.
[16:06] - It's,
[16:08] - he identified it, I think, through,
[16:12] - so called carbon stars. These are,
[16:15] - extremely red, the very luminous stars at the
[16:18] - end of their lives,
[16:20] - and which,
[16:22] - we're we're seeing on on through
[16:25] - the bulge of our own galaxy on the
[16:27] - other side of our galaxy, and and this
[16:30] - was identified. And
[16:32] - it's going on
[16:33] - a polar orbit and has left these,
[16:35] - several,
[16:37] - streams after it.
[16:39] - So this is
[16:41] - probably the most recent merger because it's ongoing
[16:44] - now.
[16:46] - Probably this is,
[16:48] - Sagittarius
[16:49] - dwarf
[16:50] - will finally be totally merged into our galaxy.
[16:52] - Maybe
[16:53] - a substantial part of it has already,
[16:56] - been mixed, other stars, and it has been
[16:58] - mixed into the stars of our galaxy, but
[17:01] - it's still ongoing.
[17:02] - So this was,
[17:04] - his early work.
[17:06] - What we are also very,
[17:08] - really like is his,
[17:10] - much more recent work on
[17:12] - stellar streams in the Andromedae galaxy, the nearest
[17:17] - really big galaxy,
[17:19] - from,
[17:21] - to ours,
[17:22] - a bit bigger than our own galaxy.
[17:25] - Where he has also identified similar,
[17:28] - collision events, in the in that galaxy. So
[17:31] - it's not something only happening our in our
[17:33] - own galaxy. It happens in other galaxies too.
[17:37] - I see. And and are we confident
[17:39] - that other galaxies are also
[17:42] - being built or have been built use, by
[17:46] - hierarchical
[17:47] - accretion? Is does this seem to be a
[17:49] - universal thing in in galaxy formation?
[17:53] - Well, that it's still a subject under study,
[17:55] - of course. But,
[17:58] - for example,
[17:59] - the European Space Agency
[18:01] - is now planning this is Araki's mission to
[18:04] - be launched in 2030,
[18:06] - which will look look for,
[18:09] - features in the halos,
[18:11] - dwarf galaxies and stellar streams and around 80
[18:15] - nearby galaxies.
[18:17] - So this,
[18:18] - can be interesting in the next decade.
[18:22] - And, Amina, I wanted to ask you about
[18:24] - the sort of the significance of knowing
[18:27] - that,
[18:29] - that this
[18:30] - accretion process is occurring.
[18:34] - Does this tell us something about, you know,
[18:37] - mysteries of of the universe like like dark
[18:40] - matter?
[18:42] - You know, for example, does, hierarchical
[18:45] - accretion,
[18:47] - does it sort of agree with the idea
[18:49] - that,
[18:50] - the universe is permeated
[18:52] - by dark matter and that dark matter is
[18:55] - involved
[18:56] - in this accretion process? Does it tell us
[18:58] - something about that?
[19:01] - Yeah. I guess there are multiple ways in
[19:03] - which it tells us about,
[19:06] - dark matter. One of the things is, of
[19:08] - course, if,
[19:10] - you know, the lambda called dark matter model
[19:12] - is correct, the mergers
[19:14] - must have been important in the history of
[19:17] - galaxies. So finding the mergers is a first
[19:20] - step.
[19:20] - Right? And so this and and what we're
[19:23] - finding for the Milky Way is indeed consistent
[19:26] - with the expectations
[19:27] - of this cosmological
[19:29] - model of hierarchical
[19:31] - merging.
[19:32] - On the other hand, these streams,
[19:35] - because they are composed of stars on very,
[19:38] - similar orbits, they're very sensitive
[19:41] - to actually the nature of dark matter.
[19:44] - The cold dark matter model predicts that the
[19:47] - halos of galaxies
[19:48] - have
[19:49] - tiny,
[19:51] - substructures
[19:52] - in them in the form of dark satellites,
[19:55] - dark subhalos.
[19:56] - And if these dark subhalos come close to
[19:59] - stellar streams,
[20:01] - then they cause a perturbation.
[20:03] - It is as if these streams are moving
[20:05] - in a on on a bumpy road as
[20:08] - it were, and you would see the bumps
[20:10] - if such,
[20:12] - collisions or encounters would happen.
[20:15] - So stellar streams are also useful in this
[20:17] - context, and what people are finding
[20:20] - at the moment is that very many of
[20:22] - the streams
[20:23] - actually show signs of perturbations,
[20:26] - which is very interesting,
[20:28] - except that for at the moment, it's hard
[20:31] - to disentangle
[20:32] - what are the sources of the perturbations.
[20:34] - So we're really working out what other ways,
[20:38] - could be,
[20:40] - could actually cause,
[20:42] - the the the features that we see in
[20:44] - the streams. It might be these dark matter
[20:46] - subhalos, but we're not certain yet.
[20:50] - I see. And and so
[20:53] - so when you look at a galaxy
[20:54] - or at the Milky Way,
[20:57] - your
[20:59] - I suppose your interpretation
[21:01] - of the structure would would lean towards,
[21:05] - cold dark matter rather than, you know, for
[21:08] - example, the theory of modified gravity,
[21:11] - like MOND,
[21:13] - the hierarchical
[21:14] - accretion.
[21:16] - Should it be interpreted as, well proof is
[21:18] - probably a strong word for dark matter rather
[21:21] - than evidence for,
[21:24] - MOND? Or or are the things that you're
[21:26] - looking at maybe too
[21:28] - or the or the the the length scales
[21:30] - too small to really tell you anything about
[21:33] - something like MOND?
[21:36] - So so in fact, I think MOND,
[21:38] - can be tested. We've also tested our, MOND
[21:42] - using stellar streams,
[21:44] - and we find we find it's not a
[21:47] - very good description
[21:48] - actually of the motions of stars in stellar
[21:51] - streams.
[21:52] - But that doesn't rule out that there may
[21:54] - be other theories, alternative theories of gravity that
[21:58] - could explain what we see around us. I
[22:01] - think
[22:02] - if we have an alternative model, it probably
[22:05] - will be very close to the Lambda CDM
[22:08] - model because,
[22:10] - you know, the it works. It seems to
[22:13] - it's not proof, like you say, because that's
[22:15] - too strong, but, certainly, there is consistency
[22:18] - as far as we can tell.
[22:21] - And,
[22:22] - there must be lots that we don't know
[22:26] - about the Milky Way.
[22:30] - Amina,
[22:31] - what's the big mystery for you? What's the
[22:33] - mystery that you would like to solve,
[22:36] - you know, if if you had the chance?
[22:40] - I guess there are quite a few mysteries.
[22:42] - I think I I can think of a
[22:44] - couple. One is indeed the nature of dark
[22:46] - matter. Right? So using streams to really constrain
[22:50] - if,
[22:51] - establish if there are these dark matter clumps
[22:54] - orbiting in the halo of our galaxy.
[22:57] - That is one really big question.
[23:00] - But also going further back in time, we've
[23:03] - been discussing,
[23:04] - you know, the last merger that we know
[23:06] - of, last big merger ten billion years ago.
[23:09] - What happened before that? And that's actually rather
[23:13] - hard,
[23:15] - to figure out because
[23:17] - at the early epochs, the universe was a
[23:19] - lot denser, so mergers
[23:21] - were happening a lot more often. And then
[23:24] - you also get mergers of similar object
[23:27] - in terms of their sizes or masses.
[23:30] - So it becomes all rather,
[23:32] - difficult to disentangle.
[23:34] - But I think
[23:35] - with the new,
[23:37] - Gaia data releases,
[23:40] - and also with new surveys giving us chemistry,
[23:43] - I'm hopeful that we can push the boundary
[23:45] - much further back in time.
[23:48] - And and we've been talking about, I suppose,
[23:50] - the history or the archaeology
[23:53] - of the Milky Way.
[23:55] - What what does
[23:56] - your research and the research of your of
[23:59] - your colleagues, the other laureates, what does it
[24:02] - tell us about the fate of the Milky
[24:04] - Way? I mean, do you think is it
[24:05] - gonna keep going
[24:07] - on accreting
[24:09] - dwarf galaxies, or has it hoovered up all
[24:12] - the dwarf galaxies that are available?
[24:14] - And, you know, it's it it'll
[24:16] - go into a different phase of its existence,
[24:19] - or maybe it's in that
[24:21] - sort of steady phase at the moment. What
[24:24] - what what's going to happen to the Milky
[24:26] - Way?
[24:28] - So as as Per was saying,
[24:31] - it's currently eating up Sagittarius.
[24:34] - Right? So I think it will be one
[24:36] - more passage of the dwarf and it will
[24:38] - be gone. It will be completely dissolved.
[24:43] - What we're seeing is it's actually interacting with
[24:46] - the large and small Magellanic
[24:48] - clouds.
[24:49] - And these are more massive, so that also
[24:51] - leaves an imprint on the on the Milky
[24:54] - Way. We can actually see a response of
[24:56] - the Milky Way to their present
[24:58] - presence.
[24:59] - So that is, the next
[25:02] - merger.
[25:04] - And then in the in the future,
[25:07] - what we see is also,
[25:09] - you know, our neighbor that also Rodrigo Ibotta
[25:12] - has studied, the m 31 galaxy, the Andromeda
[25:15] - galaxy.
[25:16] - And it's very likely that the Milky Way
[25:18] - and Andromeda will actually merge in the future.
[25:23] - But the sky will look rather different,
[25:26] - at the time because the moment you merge
[25:28] - two systems of similar size, the discs are
[25:31] - very perturbed,
[25:33] - and so we may end up in an
[25:35] - elliptical galaxy. But, you know, it's a long
[25:38] - way down the road.
[25:40] - I see. Okay. And and what about you,
[25:42] - Per? What's,
[25:43] - I mean, what would you like to see
[25:45] - in terms of Milky Way
[25:47] - research or, you know, research on galaxies in
[25:50] - general? What what what what's your wish list?
[25:52] - What would you like to see
[25:54] - happen in the future of research?
[25:57] - Well, as a cosmologist,
[25:59] - I'm most intrigued really by,
[26:04] - the the work which Amina and her colleagues
[26:06] - are doing,
[26:07] - on what what it can say about the
[26:09] - nature of the dark matter. That is really,
[26:14] - because
[26:15] - there have been a number of of
[26:18] - problems with the Lambda CDM model, which
[26:21] - grew up in the nineteen nineties and really
[26:24] - was
[26:25] - and so is,
[26:27] - to from the late nineteen nineties,
[26:29] - have been the
[26:30] - really leading theory.
[26:32] - And I want to see that dead in
[26:34] - some way, because it's been with us for
[26:37] - so long now.
[26:38] - No. It it gives a very, very good
[26:41] - description of,
[26:43] - of our observations,
[26:45] - but I would hope to find something fishy
[26:48] - there. And,
[26:50] - what has been looked upon as a problem
[26:52] - was what, Amina
[26:54] - mentioned that,
[26:55] - the the the theory predicts
[26:58] - very many more dwarf galaxies
[27:01] - than we see. And the way out of
[27:03] - that is to say that, well, they are
[27:05] - there in dark matter, but they are not
[27:07] - there in stars. They they they don't have
[27:09] - stars.
[27:11] - And,
[27:12] - if, I mean, I've, said we can study
[27:16] - this further in the by the stellar streams.
[27:18] - That is something I'm looking forward to see.
[27:22] - Well, that's great. I mean, it sounds like,
[27:24] - there's lots more to know about the Milky
[27:27] - Way.
[27:28] - Amina, congratulations
[27:30] - again
[27:31] - on,
[27:32] - winning or sharing this year's,
[27:35] - Kavli Prize in astrophysics.
[27:37] - And, Per, thank you, and to Amina for
[27:41] - coming on the podcast.
[27:43] - Thank you.
[27:44] - Thank you.
[27:53] - That was the astronomer
[27:54] - Amina Helmi
[27:56] - who shares the 2026
[27:58] - Kavli Prize in Astrophysics
[28:01] - with Vasili
[28:02] - Balakarov
[28:03] - and Rodrigo
[28:05] - Ibadah.
[28:06] - We were joined by Per Barth Lilia, who
[28:09] - is chair of the twenty twenty six
[28:12] - Kavli Prize Committee in Astrophysics.
[28:16] - Congratulations
[28:17] - to Amina, and thanks to both of my
[28:20] - guests for their insights into the Milky Way.
[28:24] - This episode is sponsored by the Kavli Prize,
[28:27] - which honors scientists for breakthroughs in astrophysics,
[28:31] - nanoscience,
[28:32] - and neuroscience,
[28:34] - transforming our understanding of the big, the small,
[28:38] - and the complex.
[28:39] - The vision for the Kavli Prize comes from
[28:42] - Fred Kavli, a Norwegian
[28:44] - American
[28:45] - entrepreneur
[28:46] - and philanthropist
[28:47] - who turned his lifelong
[28:49] - fascination with science
[28:51] - into a lasting legacy for recognizing
[28:54] - scientific breakthroughs
[28:55] - and for supporting basic research.
[28:59] - I'm afraid that's all the time we have
[29:01] - for this week's podcast.
[29:02] - I'm Hamish Johnston, and our producer is Fred
[29:05] - Iles.
[29:06] - The music in this episode was composed and
[29:09] - performed
[29:10] - by the physicist
[29:12] - Philip Moriarty,
[29:13] - and it's called
[29:15] - one three seven.
[29:17] - We'll be back again next week.

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