# Ken’ichi Nomoto and Stanford Woosley share the 2026 Shaw Prize in Astronomy

An episode of [Physics World Weekly Podcast](https://invisiblenetwork.ai/podcast/1400686733), 18 Jun 2026, 48 min.

Audio: https://media.blubrry.com/physicsworldweeklypodcast/content.blubrry.com/physicsworldweeklypodcast/PWWeekly16June2026ShawPrize.mp3

Pair are honoured for their work on supernovae and nucleosynthesis

## Transcript

[0:08] - Hello, and welcome to this episode of the
[0:11] - Physics World weekly podcast,
[0:13] - which is sponsored
[0:14] - by the Shaw Prize Foundation.
[0:17] - I'm Hamish Johnston, and my guests are Kenichi
[0:21] - Namoto
[0:22] - and Stanford Woosley,
[0:24] - who share the 2026
[0:28] - Shaw prize in astronomy
[0:30] - for their studies
[0:31] - of stellar explosions
[0:33] - and the origin of the elements.
[0:37] - The Shaw prize is an international prize based
[0:40] - in Hong Kong.
[0:42] - Currently, it consists of three annual awards.
[0:46] - These are the prize in astronomy,
[0:49] - the prize in life science and medicine,
[0:53] - and the prize in mathematical sciences.
[0:57] - In 2027,
[0:59] - a fourth prize will be awarded for work
[1:03] - in computer science.
[1:05] - Each prize carries a monetary
[1:07] - award of 1,200,000
[1:11] - US dollars.
[1:13] - The prize was established
[1:14] - by Ranran Shah, a media mogul and philanthropist.
[1:19] - It was first awarded in 2004,
[1:22] - and since then, 121
[1:26] - prizes
[1:27] - have been given
[1:28] - to individuals
[1:29] - from across the world.
[1:32] - Kenichi Nomoto is emeritus professor
[1:36] - and visiting senior scientist
[1:38] - at the Kavli Institute
[1:40] - for the Physics and Mathematics
[1:43] - of the Universe
[1:44] - at Japan's
[1:46] - University of Tokyo.
[1:48] - Stanford Woosley
[1:50] - is professor of astronomy and astrophysics
[1:53] - at the University of California,
[1:56] - Santa Cruz
[1:57] - in The US.
[1:59] - Because of the large time differences between Tokyo,
[2:03] - California,
[2:04] - and my location
[2:06] - in The UK,
[2:08] - I was unable to speak to Stan and
[2:10] - Ken
[2:11] - at the same time.
[2:13] - Instead,
[2:14] - I spoke to them separately
[2:16] - for this podcast.
[2:26] - Hi, Stan. Welcome to the podcast. My first
[2:28] - question is for you.
[2:31] - Good morning, Hamish. Nice to see you.
[2:34] - So, Stan, can you give us an introduction
[2:36] - to the field?
[2:38] - What are supernovae,
[2:39] - and why do astronomers study them?
[2:43] - Well, you know, the the word kind of
[2:44] - explains it, supernova.
[2:46] - Nova,
[2:47] - a new star in the sky and super
[2:50] - really, really bright.
[2:51] - And,
[2:52] - you know, that's that's how they operate. We
[2:54] - see suddenly
[2:55] - a new a new star appear in the
[2:57] - sky.
[2:58] - About,
[2:59] - 10 times in the last
[3:01] - two thousand years, we've recorded them, though they've
[3:04] - been going on for billions of years before
[3:06] - that.
[3:07] - But it's kind of a misnomer
[3:10] - because a supernova is not a new star,
[3:12] - it's actually the death
[3:14] - of an old star.
[3:16] - And in these explosive deaths,
[3:19] - the explosions can shine with a luminosity a
[3:21] - billion times that of the sun.
[3:24] - But they're very far away because, you know,
[3:26] - the Milky Way galaxy's 100,000
[3:28] - light years across,
[3:29] - and they're scattered around that, so the ones
[3:31] - we see are mostly nearby. So even though
[3:34] - they happen every fifty years, we've only seen
[3:37] - about 10 of them in in recorded history.
[3:40] - Some of the brightest, like in October,
[3:42] - were so bright you could see them in
[3:44] - the daytime for about a month. The the
[3:46] - Crab was that way.
[3:48] - But most of the supernovae we see nowadays
[3:51] - are in other galaxies.
[3:53] - The most recent naked eye supernova was, supernova
[3:56] - 1987
[3:57] - a.
[3:58] - And I had to go down to Australia
[4:00] - to see it, but it was quite a
[4:01] - sight, a little little red jewel in the
[4:03] - middle of the Large Magellanic Cloud about as
[4:06] - bright as a star in the handle of
[4:07] - the Big Dipper.
[4:09] - But in 1987,
[4:11] - we discovered about 25 supernovae altogether.
[4:15] - This year, there will be thousands.
[4:17] - And next year, there will be tens of
[4:18] - thousands, and there's even a projection of maybe
[4:20] - a million a year in the not too
[4:22] - distant future.
[4:23] - It's incredible.
[4:25] - How many supernovae are there really? There's there's
[4:27] - about one per second in the observable universe.
[4:30] - That's an amazing number to get your head
[4:32] - around it. Somewhere
[4:34] - in in the observable universe, which is how
[4:37] - far light has gone since the big bang,
[4:40] - a star is dying catastrophically
[4:42] - and shining with a billion times the luminosity
[4:44] - of the sun.
[4:46] - Well, we see these events and astronomers in
[4:48] - their great creativity
[4:50] - have categorized them as thing one and thing
[4:52] - two,
[4:53] - or type one and type two we call
[4:55] - them. And type two supernova is one that
[4:58] - has hydrogen
[5:00] - in its spectrum,
[5:02] - kinda like the sun. The sun is mostly
[5:03] - hydrogen on its surface. In a type two
[5:05] - supernova,
[5:06] - apparently, the surface is not completely burned up
[5:09] - and we still see the the stuff it
[5:11] - was born with.
[5:12] - The other kind, type one, you don't see
[5:15] - hydrogen.
[5:16] - It's some kind of more evolved star.
[5:18] - And we know now, especially from supernova nineteen
[5:22] - eighty seven a,
[5:23] - that the type two supernovae are the deaths
[5:25] - of massive stars,
[5:27] - things much bigger than the sun. We saw
[5:30] - the progenitor of the explosion in that case.
[5:32] - It was
[5:33] - a a 20 solar mass blue supergiant, so
[5:36] - sort of sort of like Betelgeuse but only
[5:38] - blue.
[5:39] - So there's also two categories, I'm sorry to
[5:43] - say, to complicate things of type one. There's
[5:45] - one a and one b. Neither one has
[5:47] - hydrogen, but one b
[5:49] - systematically goes with the type twos. It's it's
[5:52] - a massive star explosion,
[5:54] - where the type one a's are something totally
[5:56] - different. They're exploding white dwarf stars,
[5:59] - and we've never seen the progenitor of a
[6:01] - type one a supernova.
[6:03] - So we infer a lot from the models.
[6:05] - There's a lot of observations, but we still
[6:07] - haven't seen the progenitor just before it blew
[6:10] - up in that case.
[6:12] - Now supernovae are not only big and bright
[6:15] - and and very impressive. And by the way,
[6:17] - the sun will never be a supernova. It's
[6:19] - it's not big enough. It'll end up as
[6:21] - a white dwarf. It's only the rare massive
[6:24] - stars that become supernovae type too.
[6:27] - But they they do other things besides glow
[6:29] - brightly. They also give birth to to some
[6:32] - of the most exotic objects in the universe,
[6:35] - black holes and neutron stars.
[6:37] - When we look in the the remnant of
[6:39] - the Crabbe supernova,
[6:41] - we see a pulsar,
[6:43] - a a rapidly rotating neutron star 33 times
[6:46] - a second. And we see black holes of
[6:49] - of several and sometimes ten, twenty solar masses
[6:53] - scattered around our galaxy. And the only way
[6:55] - those can have been made is in supernovae.
[6:57] - So they not only
[6:59] - are dramatic explosions and brilliant, but they they
[7:01] - leave behind very interesting,
[7:04] - objects.
[7:05] - But the final thing which I find most
[7:07] - interesting, and and this is largely what Ken
[7:09] - and I have been noted for,
[7:11] - is that they are fountains of creation. They
[7:13] - they make the heavy elements.
[7:15] - The stuff you and I and the ocean
[7:17] - and the earth and the mountains are made
[7:18] - out of, it was almost all made in
[7:21] - a 100,000,000
[7:22] - supernovae before the sun was born.
[7:24] - And so we are stardust or or more
[7:27] - correctly, we're actively
[7:28] - star fallout.
[7:31] - And and, Stan, what was it like in
[7:34] - 1987?
[7:36] - I assume by that time, you had you
[7:39] - had studied
[7:40] - supernovae,
[7:42] - for some time. And then you went to
[7:44] - Australia, and you actually got to to see
[7:47] - one. That must have been
[7:49] - I mean, that must have been a very
[7:51] - exciting
[7:52] - time for you, was it?
[7:54] - I should say see one with your with
[7:55] - the naked eye. I'm sure you've seen them
[7:57] - in telescope images. Supernova eighty seven a was
[8:00] - was simply amazing. I couldn't believe it. I
[8:03] - thought it must be a joke. I saw
[8:04] - someone sent around an IU circular, bathed it
[8:07] - up. And when it became real, my whole
[8:09] - life changed. And and for for so many
[8:11] - of us, it was such an international collaboration.
[8:14] - You know? There were observations coming from X-ray
[8:17] - satellites in Japan and supernova
[8:20] - observatory observations in South Africa and Chile,
[8:24] - and, gamma rays were being observed from the
[8:26] - Mir spacecraft by the Soviet Union. And we
[8:29] - were all collaborating. It was just one great
[8:31] - big happy party, and that went on for
[8:34] - a couple of years. And I I traveled
[8:35] - all over the place,
[8:37] - and one of them was to Australia
[8:40] - where I got to the privilege of of
[8:42] - going out in a field with Rob McNaught,
[8:44] - who actually was one of the discoverers
[8:46] - of the
[8:48] - of of supernova eighty seven. Ian Shelton actually
[8:51] - discovered it, but Rob McNaught, by peculiarity and
[8:53] - history, saw it first and didn't realize it.
[8:56] - But he showed me
[8:57] - my first real supernova and pointed out the
[9:00] - LMC because
[9:01] - being from California, I'd never
[9:03] - seen it. And sure enough, you could see
[9:05] - this little red jewel shining right in the
[9:07] - middle of that cloud. And it was it
[9:10] - was really an impressive thing. You know, I
[9:11] - study these things in in theory all my
[9:14] - life and here here was one shining that
[9:16] - I could actually reach out and see.
[9:18] - And and that's you you've touched on an
[9:21] - interesting point about supernovae as well that
[9:24] - that people
[9:26] - observe them across many different,
[9:29] - wavelengths of light. And I think am am
[9:32] - I right in thinking we've also seen neutrinos
[9:34] - from,
[9:36] - from events as well?
[9:38] - Yeah. I that was the most incredible part
[9:40] - of all, and I'm sorry I omitted that.
[9:43] - But in in,
[9:45] - Kamiokande,
[9:46] - in Irvine, Michigan, Brookhaven, in,
[9:50] - Mount Blanc, they saw neutrinos
[9:52] - from '87 a about a dozen, but this
[9:55] - was an event a 160,000
[9:57] - light years away, and a neutrino can go
[9:59] - through a light year of lead.
[10:01] - So just to capture that dozen was an
[10:03] - incredible feat and it told us that, yeah,
[10:06] - you're you're you're kind of right.
[10:08] - These supernova happen when the core of a
[10:10] - massive star collapses to a neutron star
[10:13] - and radiates away
[10:16] - 20% of the rest mass of the sun
[10:18] - in neutrinos.
[10:20] - Incredible.
[10:22] - Ken,
[10:22] - much of your career has focused on type
[10:25] - one a supernovae.
[10:27] - Can you describe
[10:29] - this phenomenon?
[10:30] - Okay. The there exists two types of supernovae,
[10:34] - basically.
[10:35] - And,
[10:36] - food's
[10:37] - spectra shows the existence of hydrogen and helium,
[10:41] - which are called type twos.
[10:43] - And, type one
[10:45] - does not show hydrogen or helium.
[10:48] - The hydrogen and the helium are formed from
[10:50] - the big barn,
[10:52] - so normal stars should have hydrogen and helium.
[10:58] - So without hydrogen helium,
[11:00] - the exploding stars of type one a should
[11:04] - be
[11:04] - a very special
[11:06] - supernova,
[11:07] - and that is quite rough.
[11:10] - And,
[11:11] - so let me explain why
[11:13] - there exist basically two types of supernovae
[11:18] - without without without without hydrogen, for example.
[11:24] - And, then it depends on the stellar evolution.
[11:27] - The
[11:28] - evolution of stars from its birth to the
[11:31] - end
[11:33] - depends on the mass of the high mass
[11:35] - of the stars that
[11:37] - formed from the interstellar gas.
[11:39] - And,
[11:40] - so if the stars,
[11:43] - more massive than
[11:45] - 10 solar mass solar mass mass of the
[11:48] - sun,
[11:50] - Then
[11:51] - the,
[11:52] - stars are big enough to contract
[11:55] - and eventually forming iron
[11:58] - in the core and collapse and
[12:00] - to become a type two supernovae.
[12:03] - And,
[12:05] - the stars below eight solar eight solar mass,
[12:09] - like the sun, our sun,
[12:11] - we
[12:12] - it was deep completely differently.
[12:16] - They are not
[12:17] - heavy enough
[12:19] - to continue to contract.
[12:22] - So
[12:23] - the
[12:25] - the pressure of electrons
[12:27] - are strong enough
[12:28] - to prevent the contraction
[12:30] - after
[12:31] - carbon and oxygen core is formed from
[12:35] - the burning of helium.
[12:37] - And,
[12:40] - then
[12:42] - the the star, for example,
[12:45] - future sun consists of
[12:47] - the core
[12:48] - of the, carbon and oxygen
[12:51] - and
[12:51] - plus
[12:52] - envelope which contains,
[12:54] - basically, hydrogen and helium.
[12:57] - And the core is contracting, and the envelope
[13:01] - of hydrogen and helium
[13:03] - expands
[13:03] - to a to to be a so called
[13:05] - red giant.
[13:07] - And, eventually,
[13:09] - those hydrogen helium envelope is lost from the
[13:12] - core
[13:13] - by the pressure of the radiation, the pressure
[13:16] - of the
[13:17] - photons. And
[13:19] - then
[13:20] - the the star becomes just the core
[13:24] - of an ocean,
[13:26] - and which which is just going to cool
[13:29] - down,
[13:30] - becoming a white dwarf. Dwarf means, the compact
[13:34] - star, like the size of the the Earth.
[13:38] - But the mass is
[13:40] - or be about point six four mass of
[13:42] - the sun, but
[13:45] - it's very,
[13:46] - dense, that compass system.
[13:49] - Yeah, that is a white dwarf.
[13:52] - So
[13:54] - in that sense,
[13:55] - just start divided into the,
[13:58] - type two supernovae and the formation of the
[14:00] - white dwarf.
[14:02] - Two types, basically.
[14:04] - And, which I I will discuss later, the
[14:07] - stars between
[14:08] - eight to tensor mass
[14:11] - also evolved a bit it's differently, including electron
[14:14] - capture supernovae, which I I will discuss later.
[14:18] - The white dwarf itself is just cooling stars
[14:21] - and does not does not explode.
[14:24] - In other words, the sun does not become
[14:26] - a supernova.
[14:28] - But if the white dwarf is
[14:31] - included in the closed binaries,
[14:35] - there is a companion
[14:36] - stars that
[14:38] - they,
[14:39] - trigger the explosion of white dwarf, which I
[14:41] - will discuss later.
[14:43] - Yeah.
[14:45] - So but that's why
[14:47] - there's the two types of the final fate
[14:49] - of the stars,
[14:51] - very massive type two supernovae and, very small
[14:53] - mass white dwarfs.
[14:55] - And,
[14:56] - in binaries, that could become type one, a
[14:58] - supernovae.
[15:00] - And, Ken, I wanted to ask you about
[15:02] - a very famous
[15:04] - supernova called the Crab
[15:06] - supernova, which I think you have done a
[15:08] - lot of work on.
[15:10] - This is thought to
[15:12] - have been created
[15:14] - by or or I should say the Crab
[15:15] - Nebula Mhmm. Is thought to have been created
[15:18] - by an electron
[15:20] - capture
[15:21] - supernova. Can can you talk a bit about
[15:23] - that event?
[15:24] - Okay.
[15:25] - The
[15:26] - the cloud is,
[15:28] - very well observed, but
[15:31] - and data
[15:32] - clearly
[15:33] - a remnant of the supernova explosions
[15:36] - because that forms a neutron star inside
[15:39] - that is very clearly seen. But as the
[15:42] - klebonylure is not not a typical
[15:45] - remnant of supernova explosions
[15:47] - because
[15:49] - its expansion
[15:51] - energy is
[15:54] - less than
[15:55] - 10 times less than the ordinary supermodel elements,
[15:58] - very weak explosions.
[16:00] - And it contains not much heavy elements,
[16:04] - which should have been produced in the explosion
[16:07] - ordinary supermodel,
[16:08] - but crab doesn't.
[16:10] - So their CREB is very different from
[16:14] - typical
[16:15] - supernova remnant.
[16:18] - Then
[16:19] - the case of the,
[16:21] - the electron capture supernovae,
[16:23] - which I mentioned,
[16:25] - comes from the stars between
[16:28] - probably around nine solar mass.
[16:31] - The as I said, the
[16:35] - the stars
[16:36] - between eight solar mass and 10 solar mass,
[16:39] - they
[16:40] - burn carbon
[16:42] - during its evolution and forming
[16:44] - the core of oxygen,
[16:46] - neon, magnesium.
[16:49] - And
[16:51] - then
[16:53] - the
[16:54] - the contraction of
[16:56] - the core stops.
[16:58] - So, basically,
[16:59] - the for example, eight to
[17:02] - nine for a mass case, lower lower side
[17:04] - of of that mass range
[17:07] - becomes
[17:09] - a forming
[17:11] - oxygen near magnesium white dwarf,
[17:14] - similar to the carbon oxygen white dwarf below
[17:18] - eight for a mass. But
[17:19] - the
[17:21] - stars,
[17:22] - for example, around nine to 10 solar mass,
[17:24] - slightly above it,
[17:27] - we can contract
[17:28] - to a very high density.
[17:31] - And
[17:33] - the density becomes high enough
[17:36] - for the electrons
[17:39] - captured
[17:40] - absorbed by
[17:42] - the neon and magnesium, for example.
[17:45] - So the number of number fraction of electron
[17:48] - decrease.
[17:49] - So the pressure
[17:51] - of electrons decrease, and that
[17:54] - induce the collapse
[17:56] - of the oxygen near magnesium core.
[17:59] - And that makes,
[18:00] - white are the explosions supernova type
[18:04] - basically, type two similar to type two,
[18:07] - but
[18:08] - the
[18:09] - the collapsing core of oxygen near magnesium
[18:12] - is
[18:14] - smaller than iron core.
[18:17] - So its explosion energy
[18:19] - in in calculation
[18:21] - is quite small
[18:23] - and less than 10 times
[18:26] - 10 times less than the water in super
[18:28] - explosion models.
[18:30] - And,
[18:31] - also,
[18:32] - it ejects
[18:33] - only the outer envelope
[18:35] - material,
[18:36] - so not much heavy elements.
[18:39] - So so those features,
[18:42] - not typical
[18:44] - compared with the ordinary,
[18:46] - super type two supernova explosions,
[18:50] - but it's very similar to the for what
[18:53] - we are observing in kravniviera.
[18:56] - Both
[18:57] - are different from typical one.
[19:00] - Observationally,
[19:01] - not typical,
[19:02] - and, electron capture superman will be theoretically not
[19:05] - typical.
[19:07] - So that's why I suggested
[19:09] - the Crab Nebula is formed from
[19:12] - the,
[19:14] - electron capture supernovae
[19:15] - around probably nine to 10 solar mass range,
[19:19] - lower end of the quark supernovae.
[19:22] - And that's, Ken, that's one thing that I
[19:24] - really like about
[19:25] - supernovae
[19:26] - is that
[19:27] - it's a lot of nuclear physics, isn't it?
[19:30] - I mean, do you consider yourself a a
[19:32] - nuclear
[19:33] - physicist?
[19:34] - Is that how you would describe yourself? Or
[19:36] - are you more of an astrophysicist?
[19:38] - Because I'm guessing you spent a lot of
[19:40] - time
[19:42] - doing nuclear physics. I am astrophysicist
[19:45] - and
[19:46] - kind of user of nuclear physics.
[19:49] - So I have to know
[19:51] - the new the physics of nuclear
[19:54] - nuclear materials and
[19:56] - for the equation of state and so on,
[19:58] - but
[20:00] - and the nuclear reactions.
[20:02] - But,
[20:03] - we are not
[20:04] - developing reaction rate by by ourselves.
[20:07] - So we we believe
[20:10] - a nuclear physicist can do it properly.
[20:13] - Well, that's great. We're gonna talk we're gonna
[20:14] - talk some more,
[20:16] - about,
[20:17] - nuclear physics and nucleosynthesis
[20:19] - a bit later in the podcast.
[20:22] - But now I'm going to go, my next
[20:24] - question
[20:25] - is for Stan.
[20:27] - Stan, you've done a lot of work on
[20:29] - type two
[20:30] - supernovae.
[20:31] - What distinguishes
[20:32] - these,
[20:33] - events from type one a
[20:36] - supernovae?
[20:37] - Well, type type one a is is an
[20:39] - entirely different thing.
[20:41] - It's the explosion of a white dwarf interacting
[20:43] - in a binary system,
[20:45] - as as Ken has been describing.
[20:47] - A type two and and a 1b also,
[20:51] - is the end of the life of a
[20:53] - star more than eight times the mass of
[20:55] - of the sun.
[20:56] - The sun is not big enough to become
[20:59] - a supernova.
[21:00] - It can fuse hydrogen to helium like it's
[21:03] - doing now and will for five billion more
[21:05] - years, and then it can turn helium into
[21:07] - carbon and oxygen,
[21:09] - but that's the end of the road for
[21:10] - the sun. It's just not big enough to
[21:12] - go on. But massive stars fuse carbon into
[21:16] - neon and magnesium and oxygen into silicon and
[21:19] - sulfur and silicon into
[21:21] - iron. And so, you know, it just keeps
[21:23] - on going, but there is an endpoint
[21:25] - in that once you've made iron, you can
[21:27] - get no more energy out of nuclear fusion.
[21:30] - So you end up with a star with
[21:31] - a composition kind of like a spherical layer
[21:34] - cake or a Russian doll set with a
[21:36] - core of iron and a shell of silicon
[21:38] - and a shell of oxygen and so on.
[21:40] - But the iron core can't support itself, it
[21:43] - has no more source of nuclear energy,
[21:45] - so it collapses and there's nothing to stop
[21:47] - the collapse and it collapses all the way
[21:49] - to the density of the atomic nucleus to
[21:51] - a neutron star.
[21:53] - And in the process, it radiates, as we
[21:55] - mentioned before, this stupendous flux of neutrinos.
[22:00] - 10 to the 58 of them, I believe
[22:02] - it is. 20% of the rest mass of
[22:04] - the sun.
[22:06] - And those neutrinos,
[22:07] - for the most part, just stream out and
[22:09] - are never seen again.
[22:11] - But of the order 1% of them capturing
[22:13] - the material outside of this collapsing iron core
[22:17] - and push on it and cause a shockwave
[22:19] - to be born. And so it pushes out
[22:21] - all of these ashes of the previous burning
[22:23] - of carbon burning and oxygen and silicon burning,
[22:27] - pushes them out into the interstellar medium and
[22:29] - it also pushes out some radioactive nickel 56.
[22:33] - And it makes a shockwave that interacts with
[22:35] - the envelope of the star
[22:37] - and as that envelope expands and dumps the
[22:40] - energy that the shockwave deposited,
[22:42] - you get a long, several month long, very
[22:44] - bright supernova.
[22:46] - And then the radioactive nickel, which we've actually
[22:48] - seen in many supernovae now, makes a tail
[22:51] - on that light curve.
[22:53] - And so go you go back
[22:55] - millennia later and you see the neutron star
[22:57] - there or maybe a black hole got made
[23:00] - and you see this remnant of of ashes
[23:04] - expanding at thousands of kilometers per second made
[23:07] - out of silicon, sulfur, and and so on,
[23:10] - the stuff that someday will make a million
[23:12] - Earths.
[23:13] - And so it it turns out that a
[23:15] - type two supernova,
[23:17] - although not widely appreciated, is is mostly a
[23:20] - neutrino explosion.
[23:21] - Most of the energy comes out in in
[23:23] - neutrinos.
[23:25] - 1% of that energy comes out in the
[23:27] - kinetic energy of the explosion,
[23:30] - and then 1% of that comes out as
[23:32] - the light.
[23:34] - And so bright as they are, the light
[23:36] - is sort of an afterthought, you know, point
[23:37] - o 1% of the actual explosion. It's really
[23:40] - a neutrino bomb,
[23:42] - and,
[23:43] - the kinetic energy is 1% of that.
[23:46] - And it sounds to me that there's a
[23:48] - lot of of nuclear physics going on here.
[23:52] - I mean, our our our supernovae, are they,
[23:55] - like a
[23:56] - a
[23:57] - a distant
[23:58] - laboratory that you can study
[24:01] - ideas of nuclear physics?
[24:04] - They they are the ultimate nuclear physics laboratory.
[24:07] - Everything reacts with everything.
[24:10] - The first three years of my research in
[24:12] - supernovae, I worked with,
[24:14] - Willie Fowler at Kellogg lab calculating the nuclear
[24:17] - reaction rates
[24:18] - for all of the things that go into
[24:20] - the nuclear synthesis that goes on these stars.
[24:22] - That's how I got started in
[24:23] - in my in my studies.
[24:26] - And you can have, as I mentioned, all
[24:28] - of the elements from from helium to to
[24:30] - nickel and beyond
[24:32] - interacting with neutrons, protons, and alpha particles.
[24:35] - There are literally tens of thousands of nuclear
[24:38] - reactions going on and keeping track of all
[24:40] - of them and seeing what comes out
[24:42] - is really a task for a big computer.
[24:45] - But yeah, they're type one a supernovae, especially,
[24:48] - are thermonuclear
[24:49] - bombs. They're entirely powered
[24:51] - by nuclear reactions.
[24:52] - In the type twos,
[24:54] - it's more, a neutrino event, as I said,
[24:57] - so there's a lot of particle physics as
[24:59] - well as nuclear physics.
[25:01] - But, yeah, just just about every nuclear reaction
[25:03] - you can think of happens in in these
[25:05] - explosions.
[25:06] - They are giant bombs.
[25:09] - So, Ken, thanks to work done by you,
[25:11] - Stan, and, of course, a lot of other
[25:14] - astrophysicists.
[25:15] - We know that,
[25:17] - some heavy elements are made during supernovae.
[25:21] - What elements are produced in type one a
[25:24] - supernovae,
[25:25] - and how are these elements produced?
[25:28] - Okay.
[25:29] - Yeah. As I said,
[25:31] - white dwarfs
[25:32] - are just cooling stars by itself
[25:34] - and doesn't explode.
[25:36] - But in close binary binaries,
[25:39] - we white dwarf had a companion star,
[25:42] - and that sent a lot of gas onto
[25:44] - the white dwarf.
[25:46] - So white dwarf mass grows
[25:48] - and becomes,
[25:49] - very much compact and becomes dense.
[25:54] - And, when there is a
[25:57] - they reach it the height of mass reaches
[25:59] - typically 1.4
[26:01] - so type for solar mass,
[26:03] - then the
[26:06] - the density in the in the central region
[26:08] - is high enough
[26:09] - for the carbon
[26:11] - to be ignited
[26:12] - by fusion.
[26:14] - And,
[26:15] - so because density is so high,
[26:18] - the white dough doesn't expand
[26:21] - because of the,
[26:24] - nuclear energy release. So nuclear energy
[26:27] - release just going to increase the temperature.
[26:30] - And
[26:31] - temperature
[26:32] - becomes so high
[26:34] - and not only carbon,
[26:36] - but also oxygen, magnesium,
[26:39] - and the silicon, and and eventually forming
[26:42] - the
[26:43] - nickel 56
[26:45] - and
[26:46] - at at almost
[26:49] - the 10 to the 10 degree in temperature.
[26:54] - And that nickel 56
[26:57] - is a radioactive
[26:58] - in this element.
[27:00] - And
[27:02] - so
[27:03] - that decays into cobalt 56,
[27:06] - which also unstable,
[27:07] - and
[27:08] - then it decays into iron 56,
[27:11] - most abundant
[27:12] - iron.
[27:14] - And,
[27:15] - so,
[27:17] - eventually,
[27:18] - type one s supernova produced lots of iron
[27:21] - because of the very high temperature
[27:23] - in the in the explosion
[27:26] - compared with more even higher than type two
[27:28] - supernova.
[27:29] - And
[27:32] - then the
[27:35] - the, the other thing is important is the
[27:38] - reductive
[27:39] - decays
[27:40] - of nickel 56 and cobalt 56.
[27:44] - They produce a lot of gamma rays
[27:46] - and the high energy X rays.
[27:49] - So that
[27:50] - provides a power for the light curve of
[27:53] - the supernovae.
[27:54] - So
[27:55] - the new in in terms of nuclear synthesis,
[27:58] - type one a supernova will produce lots of
[28:00] - iron 56
[28:02] - as
[28:02] - a decay product of the radioactive nickel 56
[28:06] - and produce some silicon sulfur, but which are
[28:10] - not much compared with the, massive explosion.
[28:15] - So the
[28:16] - in the evolution of the universe,
[28:21] - the the type one a is very special
[28:23] - role to increase the mass mass fraction of
[28:26] - the ion.
[28:29] - So so if we follow the chem so
[28:31] - called chemical evolution of galaxies,
[28:34] - we can know when type one is plasma
[28:36] - starts to increase ion
[28:39] - compared with others.
[28:40] - That is one thing. So, Ken, I I'm
[28:43] - sitting at a desk, and and the desk
[28:45] - has steel legs, which, of course, is mostly
[28:47] - iron.
[28:48] - What percentage of the iron
[28:51] - in that in those steel legs of my
[28:53] - desk do you think were made by type
[28:56] - one a
[28:57] - supernovae? Is it most of the iron, or
[29:00] - is it some of it? Could you can
[29:02] - you give a percentage? I think, this one
[29:04] - is about about 60%
[29:07] - of iron coming from
[29:09] - type one a, and,
[29:11] - this is coming from type twos.
[29:13] - Yeah.
[29:15] - Type twos also produce
[29:17] - the some iron and which is actually observed
[29:21] - in famous supernova
[29:23] - nineteen eighty seven a in Magellanic Cloud.
[29:28] - That is iron.
[29:30] - And what I wanted to say is that
[29:32] - the
[29:34] - the formation of the radioactive
[29:36] - nickel
[29:37] - to produce gamma rays are very important for
[29:39] - the brightness
[29:41] - of type one a.
[29:42] - And,
[29:43] - the white mass is very
[29:46] - relatively similar with each other.
[29:48] - It produced the mass of the
[29:51] - Nikkei 56 also similar.
[29:53] - So that makes the the brightness of type
[29:56] - one a also quite similar among them.
[30:00] - That makes the type one a a so
[30:03] - called
[30:04] - standard candle
[30:06] - for the distance measurement.
[30:08] - And that is related to the
[30:10] - the how
[30:12] - the type one a super has been used
[30:15] - to
[30:16] - to infer the distance of dark energy.
[30:19] - That's right, Ken. And that's something that we're
[30:21] - gonna talk about,
[30:22] - a bit later on in the podcast.
[30:25] - Stan, what about,
[30:27] - nucleosynthesis
[30:28] - in type two
[30:30] - supernovae? What what sort of elements are produced,
[30:33] - and and how do we know that these
[30:34] - elements are produced?
[30:36] - Most of the elements that we see in
[30:38] - in the everyday world are made in type
[30:41] - two supernovae.
[30:43] - Exceptions are hydrogen and helium, which are made
[30:45] - in the big bang.
[30:46] - And most of the iron group, but not
[30:48] - all of it, is made in type one
[30:50] - a supernova, the other kind.
[30:52] - But just about everything else, you know, the
[30:55] - most of the carbon, the oxygen, you know,
[30:57] - what we see in the ocean except for
[30:59] - the hydrogen, the mountains, our own bodies, it's
[31:02] - all made in supernovae.
[31:05] - How do we know?
[31:07] - Well,
[31:08] - several ways, but the most direct way is
[31:09] - looking at the remnants of supernovae and and
[31:11] - actually seeing,
[31:13] - as as in the Cas a supernova remnant,
[31:16] - the silicon and oxygen and and other heavy
[31:19] - elements that have been made there spewing out
[31:21] - at thousands of kilometers per second.
[31:24] - In supernova eighty seven a, we were able
[31:26] - to watch it expand and gradually uncover the
[31:28] - new elements,
[31:29] - And we actually detected the gamma rays coming
[31:32] - from the decay
[31:33] - of radioactive nickel 56 in supernova eighty seven
[31:36] - a.
[31:37] - Now that specific isotope is very interesting because
[31:40] - it it decays to iron.
[31:42] - And all of the iron in our bodies
[31:44] - and everywhere
[31:46] - has been created first as nickel 56.
[31:49] - So as I as I mentioned, we're not
[31:51] - just stardust, we are fallout. And in fact,
[31:54] - part of it is is formally radioactive fallout.
[31:57] - And and I think it's right to say
[31:59] - that,
[32:00] - some
[32:01] - heavy heavier elements
[32:03] - like gold,
[32:05] - also have a a connection
[32:07] - to type two
[32:10] - supernovae
[32:11] - because they're made in neutron stars or merging
[32:14] - neutron stars. Is that right? So there's a
[32:17] - connection there as well, isn't there? Yes. I
[32:19] - I kind of glossed over that by saying
[32:21] - the common elements of existence because
[32:24] - gold is is somewhat uncommon
[32:26] - as is platinum and so on and has
[32:29] - has has been in the news a lot
[32:30] - recently.
[32:31] - We now believe that most of those very
[32:34] - heavy elements are made,
[32:36] - by something called the r process in merging
[32:38] - neutron stars.
[32:40] - But supernovae still play a role because the
[32:42] - neutron stars came from from supernovae to start
[32:45] - with, so perhaps I wasn't stretching things too
[32:48] - much. It's just there's this other step that
[32:50] - you have to have two supernovae close to
[32:52] - each other that leave two neutron stars that
[32:55] - gradually spiral into each other and eject very
[32:58] - neutron rich matter that partially becomes gold.
[33:01] - Can you you sort of hinted earlier that
[33:04] - type one a supernovae
[33:06] - play an important role
[33:08] - in our understanding
[33:10] - of the expansion of the universe. Can you
[33:12] - explain
[33:13] - why?
[33:14] - Why are these,
[33:15] - objects so important to, cosmologists?
[33:20] - Because,
[33:22] - it's important to know the distance
[33:25] - or
[33:26] - the size of the universe
[33:27] - as a function of time
[33:29] - to understand the expansion of the universe.
[33:32] - To know the distance,
[33:35] - we should have
[33:36] - a so called standard candles, and that is
[33:39] - the luminosity is the same.
[33:42] - And,
[33:43] - if the standard candle is far
[33:45] - from us, it's faint, and it's closer, it's
[33:49] - brighter.
[33:50] - And, so measurement of the brightness of the
[33:53] - standard candles is important to know the distance
[33:57] - to the the distance of the galaxies which
[34:00] - the those standard candles are included.
[34:02] - And,
[34:03] - as I said,
[34:05] - the type one a supernova
[34:07] - is exploding white dwarfs, so then the mass
[34:09] - of the white dwarf
[34:11] - is
[34:11] - basically very similar with each other.
[34:14] - And,
[34:15] - that means that
[34:17] - produced amount of nickel 50 radioactive nickel 56
[34:20] - is also similar.
[34:22] - So that means the brightness
[34:25] - or some some even some variation, but also
[34:28] - quite similar.
[34:29] - Similar. So with with some corrections,
[34:32] - we can use
[34:35] - the observed
[34:36] - luminosity
[34:36] - brightness of type one and supernovae
[34:39] - as
[34:40] - the,
[34:41] - the constant.
[34:42] - And so
[34:45] - if we
[34:46] - so the people
[34:48] - using satellite to measure
[34:50] - the brightness of the many type one supernovae.
[34:53] - And,
[34:55] - so distant supernovae
[34:56] - type one supernovae is faint and the nearby
[34:59] - is brighter.
[35:01] - So if,
[35:02] - because the universe is now expanding,
[35:05] - the
[35:07] - the
[35:09] - in the old days,
[35:11] - the type one is super
[35:13] - at the at far far distance,
[35:16] - the is observed as the faint ones,
[35:19] - and the recent one is is
[35:21] - observed as bright one.
[35:23] - And
[35:26] - and,
[35:28] - if
[35:29] - the expansion of the universe
[35:32] - is being accelerated,
[35:35] - which we have a conclusion, but being accelerated,
[35:39] - that means,
[35:40] - in the past,
[35:42] - it's the
[35:44] - expansion
[35:45] - is slower
[35:47] - than the present.
[35:49] - From the past, it's slower and then being
[35:52] - accelerated to the current speed and then further
[35:55] - increase in exponential speed later.
[35:59] - And,
[36:00] - so that means,
[36:01] - the at the same time,
[36:03] - measured by the red circle redshift,
[36:07] - the
[36:09] - the if
[36:11] - if we compare the observed
[36:15] - supernova brightness
[36:17] - with
[36:18] - the prediction
[36:21] - without any acceleration or decelerations,
[36:27] - We know the
[36:29] - the,
[36:31] - if, okay, if the observed supernovae
[36:34] - is fainter
[36:36] - than
[36:36] - the predicted for the non accelerating universe,
[36:41] - then
[36:45] - the accelerate the expansion of the universe is
[36:48] - being accelerated.
[36:50] - In the past, it's through expansion.
[36:53] - So
[36:54] - in that way,
[36:56] - the standard candles
[36:58] - can be used
[37:01] - to decide if
[37:03] - the universe is being accelerated
[37:05] - or even
[37:08] - or decelerating
[37:09] - compared with the, nothing.
[37:13] - Just simple ex the expansion.
[37:16] - So
[37:17] - the observed group,
[37:20] - the two groups measured
[37:22] - the distant type one supernova brightness
[37:25] - and found
[37:26] - at so called redshift point 5.5,
[37:30] - the the super observable supernovae
[37:32] - is fainter significantly
[37:34] - fainter than the predicted
[37:36] - by the the,
[37:38] - non accelerating
[37:40] - expansion being universe.
[37:42] - So that faint means,
[37:44] - the in the past, expansion is slower
[37:47] - than the current one. And so the current
[37:50] - rate, the universe is being accelerated.
[37:53] - And that, of course, is a big surprise.
[37:55] - Yes. Right. Because, people believe
[37:58] - the universe has a matter.
[38:00] - So it's being even
[38:02] - decelerated
[38:03] - by the by its matter itself.
[38:06] - And,
[38:09] - so there
[38:11] - is no clear idea of what
[38:13] - is
[38:16] - the causing expansion
[38:18] - of the universe.
[38:20] - So we are calling that that is dark
[38:23] - energy. Dark energy
[38:25] - is being, decelerated
[38:27] - the universe.
[38:28] - So in a sense, supernovae are responsible
[38:31] - for,
[38:32] - perhaps one of the most profound
[38:35] - discoveries
[38:36] - in cosmology
[38:38] - in the last,
[38:39] - well, fifty years or
[38:40] - what what whatever. Yeah. So it I mean,
[38:43] - it just goes to show how important these
[38:45] - objects are,
[38:47] - to astronomy and, our understanding
[38:51] - of the universe.
[38:52] - So, Stan, what are you most excited about
[38:55] - in current
[38:56] - supernovae
[38:57] - research?
[38:59] - Well, there's so many exciting things coming up,
[39:01] - but the the first that comes to mind
[39:03] - is the,
[39:04] - Rubin Observatory
[39:06] - legacy survey of space and time, which is
[39:08] - going to discover, they say, about a quarter
[39:11] - of a million supernovae per year for
[39:14] - maybe the next ten years.
[39:16] - That's that's a huge number, obviously, and and
[39:19] - a lot of it'll just be more of
[39:21] - the same, which is interesting to people like
[39:23] - me. But the most interesting cases
[39:26] - will be the outliers with millions of supernovae.
[39:28] - There'll be thousands of
[39:30] - unusual
[39:31] - super luminous supernovae, supernovae
[39:34] - connected with gamma ray bursts,
[39:36] - supernovae with strange stars and progenitors, and so
[39:39] - on. It's enough to last
[39:42] - at least one lifetime just analyzing that, and
[39:44] - so I'm really looking forward to that.
[39:47] - Another telescope coming online is is the James
[39:50] - Webb Telescope,
[39:52] - which is very good good at looking in
[39:54] - the far infrared and seeing
[39:56] - high redshift galaxies and measuring abundances there.
[40:00] - And it's very exciting to think that we
[40:01] - can actually look back in time
[40:03] - and see when the first elements were being
[40:05] - made and the first stars, the first supernovae.
[40:08] - And so that's extremely exciting. I might I
[40:11] - might add parenthetically, this is
[40:14] - partially the reason that Ken and I got
[40:16] - the the Shaw prize,
[40:18] - was our quantitative
[40:19] - theories of nucleosynthesis.
[40:21] - For seventy years, we've we've known that, that
[40:24] - the elements are probably made in stars and
[40:27] - supernovae,
[40:28] - but now that's an absolute certainty.
[40:31] - And,
[40:32] - now it's become a quantitative field, and so
[40:34] - what we've done is to calculate
[40:37] - models for stars of different masses, supernovae of
[40:40] - different types, of all types,
[40:42] - and to add it all up and get
[40:44] - a history of the abundances in our galaxy,
[40:47] - the abundances in the sun, the abundances in
[40:49] - other galaxies.
[40:51] - So everywhere you can make a new abundance
[40:53] - determination,
[40:53] - we're we're very interested in that.
[40:56] - We're still waiting for the galactic supernova.
[41:00] - Now 87 a was close, but it's a
[41:02] - 160,000
[41:03] - light years away in in the Magellanic Cloud.
[41:06] - Supposedly, there's one every fifty years.
[41:09] - Most of them, we don't see with our
[41:11] - naked eye because
[41:13] - they're in the disc of the galaxy and
[41:15] - the dust and the gas
[41:16] - makes it hard even for a supernova to
[41:18] - be seen so far away.
[41:21] - But with neutrino observatories that are now online
[41:24] - and with gravitational radiation
[41:26] - observatories that are now online and infrared and
[41:28] - radio, we we would now see a supernova
[41:30] - anywhere in the galaxy.
[41:32] - And it happens every fifty years statistically and
[41:35] - it hasn't happened
[41:36] - in a long time.
[41:38] - And so any day now or any decade
[41:40] - now or any century now,
[41:43] - we're gonna have the next supernova and that
[41:45] - will be exciting. We'll study it close-up. We'll
[41:48] - study the neutrinos
[41:50] - carefully and finally learn you know, you can't
[41:52] - see what's going on in the middle of
[41:53] - this collapsing star.
[41:55] - Except with neutrinos, you can.
[41:57] - And so maybe we can uncover a little
[41:59] - more about what what the central engine is
[42:01] - going to do there.
[42:03] - On computers, they also get bigger and amazing
[42:06] - every year.
[42:08] - And simulations
[42:09] - in three dimensions with detailed neutrino transport
[42:13] - are starting to become available, but they're still
[42:15] - pretty primitive.
[42:17] - And after,
[42:18] - what's it been,
[42:19] - sixty years since we first had the
[42:22] - proposed model by Colgate of the neutrino transport
[42:25] - supernova,
[42:26] - which I described,
[42:27] - we still haven't
[42:29] - all in the community agreed on just which
[42:31] - stars blow up and just how
[42:33] - because it's just such a hard three-dimensional,
[42:36] - maybe magnetohydrodynamic
[42:38] - rotational
[42:39] - neutrino transport problem.
[42:41] - But the computers and the codes are getting
[42:43] - where they can do that, and so I'm
[42:45] - excited about that.
[42:47] - I'm excited about gamma ray bursts. Now this
[42:50] - is something we didn't mention much, but they're
[42:52] - an unusual kind of supernova.
[42:54] - These are really the brightest explosions in the
[42:57] - universe. They
[42:58] - they emit as much light in our direction
[43:02] - in in a few seconds as the sun
[43:04] - will put out in its ten billion year
[43:06] - lifetime multiplied by a 100.
[43:08] - And
[43:09] - I'm I'm excited about them partly because I
[43:11] - proposed the model for how they work, which
[43:14] - is that when one of these supernova collapses
[43:17] - the core, that instead of making a neutron
[43:19] - star, it makes a black hole and the
[43:20] - rest of the star falls in
[43:22] - and forms a disk around the black hole
[43:24] - and makes a little miniature quasar
[43:26] - which launches jets. And if we're in the
[43:28] - jet, we see the gamma ray burst. Well,
[43:30] - it's it's a nice story and in fact,
[43:32] - I think the community largely believes it, but
[43:34] - it's still to be completely verified.
[43:37] - There are other possibilities all involving massive stars,
[43:41] - but I'd like to see some confirmation, perhaps
[43:44] - observational of that.
[43:46] - We haven't seen the actual progenitors of type
[43:48] - one a supernova,
[43:50] - And we'd really like to, you know, get
[43:52] - a handle, if not see them directly,
[43:55] - see the companions or see evidence that this
[43:57] - nice fiction that we've built that explains so
[44:00] - much
[44:00] - of accreting white dwarfs
[44:02] - really is
[44:04] - what's going on.
[44:06] - And finally,
[44:07] - most exciting
[44:08] - today is what LIGO, Virgo, Kogra are doing,
[44:11] - watching merging black holes and studying the gravitational
[44:14] - radiation.
[44:15] - They've seen 300 black holes merge so far,
[44:18] - but they're gonna see many, many more. And
[44:20] - so we'll be able to map out the
[44:22] - distribution
[44:23] - of the black hole remnants that supernova leave
[44:26] - behind,
[44:26] - which is fascinating in itself, but also a
[44:28] - powerful constraint on what blows up and what
[44:30] - doesn't. And and, Ken, what are you most
[44:33] - excited about in current
[44:35] - supernovae research?
[44:37] - I was very much excited with the observation
[44:40] - of the type the supernova
[44:42] - '19 80 '7 a,
[44:44] - imaginary cloud,
[44:46] - because, the our colleagues in University of Tokyo
[44:49] - observed neutrinos
[44:51] - from that event, and we we are very
[44:54] - close to them.
[44:56] - And, but theoretically,
[44:58] - the
[44:59] - what I was very much excited is
[45:02] - we have I made a kind of prediction
[45:05] - of the model of type one a super
[45:07] - and b as a exploding white dwarf
[45:10] - and calculated the
[45:13] - the light carbon
[45:14] - spectra.
[45:15] - But,
[45:16] - in Japan, we didn't at that time have
[45:19] - a observer observed groups
[45:21] - of supernovae.
[45:23] - So we have no way to check. Then
[45:25] - I
[45:26] - I went to US and attended conference, and
[45:31] - then the, several people
[45:33] - told me,
[45:35] - your model
[45:37] - prediction is very much fit to the observed
[45:40] - type one super.
[45:42] - Actually,
[45:43] - the comparison my with my models with all
[45:45] - the observations
[45:47] - are in very good agreement, and that was
[45:49] - a big very big surprise and exciting
[45:53] - how my theoretical model is confirmed.
[45:56] - I didn't expect my storage model will be
[45:59] - confirmed by the observational universe.
[46:03] - So but in US, they did. So it's
[46:06] - that that is very much exciting.
[46:16] - That was Ken Namoto
[46:18] - and Stan Woosley
[46:20] - who shared the 2026
[46:22] - Shaw prize in astronomy.
[46:25] - Thanks to both of them for a fascinating
[46:27] - discussion
[46:28] - about supernovae.
[46:30] - And thanks to the Shaw prize foundation
[46:33] - for sponsoring this episode.
[46:36] - The Shaw Prize is an international
[46:38] - prize based in Hong Kong.
[46:40] - Currently, it consists of three annual awards,
[46:45] - the prize in astronomy,
[46:46] - the prize in life science and medicine,
[46:50] - and the prize in mathematical sciences.
[46:53] - In 2027,
[46:55] - a fourth prize will be awarded
[46:57] - for work in computer science.
[47:00] - Each prize carries a monetary
[47:03] - award of 1,200,000
[47:06] - US dollars.
[47:07] - The prize was established
[47:09] - by Runrun Shaw,
[47:11] - a media mogul and philanthropist.
[47:14] - It was first awarded in 2004,
[47:17] - and since then,
[47:18] - 121
[47:20] - prizes
[47:21] - have been given to individuals
[47:23] - from across the world.
[47:26] - I'm afraid that's all the time we have
[47:27] - for this week's podcast.
[47:29] - I'm Hamish Johnston, and our producer is Fred
[47:32] - Isles.
[47:33] - The music that you heard in this episode
[47:36] - is called one three seven,
[47:38] - and it was composed and performed
[47:41] - by the physicist
[47:42] - Philip Moriarty.
[47:44] - We'll be back again next week.

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