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