Supernovas: Gravity-powered Neutrino Bombs

good evening and thank you all for

coming to the latest installment of the slack public lectures we're very pleased

for those of you who are not here last time to have this beautiful new auditorium in our beautiful new

administration building and we're very glad that it accommodates a large crowd

and I think the biggest explosions in the universe bring out a large crowd so

thank you very much for being here we are very lucky this evening to have with

us dr. Alexander Freedland he grew up in Russia he came his family emigrated to

the US he got into UC Berkeley for graduate school working with the oh

maybe somewhat well-known professor higashi-murayama there in that time he

became one of the world's experts on the various interactions of neutrinos he is

responsible for discovering something called the dark side of the neutrino face base and then after that he was for

a long time a richard fineman fellow and then a permanent staff member at Los Alamos National Laboratory which is a

place that knows a lot about shockwaves explosions and such things and he

basically developed the relation between what happens inside a supernova and the

detailed micro physics of neutrinos and so that's what he'll took now he's come

back come to slack to basically help the next generation neutrino experiment

learn more about the core of supernovas a topic that he'll talk about in this talk so without further ado let me

introduce Alex and he will discuss neutrinos as gravity-powered neutrino

bombs

and you hear me now okay thank you Michael and thank you all for coming

this is obviously a crowd that's

interested in neutrinos this is also I'm this is a public lecture though this

lecture is designed to be on a certain level but if you have questions especially questions of any level no

matter how technical there is a team of ours here who will hang around after the talk and we're happy to entertain your

questions just remember that in the in during the talk and the first part of

the question session it's a public lecture well the Wizards are not allowed to do

magic we can not answer very technical questions just yet but we're happy to

discuss them them as the evening goes on so and this is a title of this lecture

now I will talk about a time of the most powerful energetic explosions in the

universe what happens when a massive star and his wife and I will convince

you that in a proper way doing these objects they are priority

powered convenor bombs so the story begins something like a hundred and

sixty six thousand years ago give or take a few thousand years though the

earth was the and an ice age and there were no telescopes or or or anything at

that time modern humans have not yet left the Africa and in a small galaxy

not too far away there was an explosion a spectacular explosion of a very very

large star and because this galaxy was a hundred and sixty-six thousand

light-years from us the light the signal of this explosion has been traveling to

us ever since and then arrived on earth on the night

of February 23rd and twenty worth in 1987 well most of the people on

this night sensible people went to sleep as they as they should if you are crazy

scientists were sitting on a mountain in South America and killing and were

looking up at the sky and observing a region of space called the Large

Magellanic Cloud and they had a rather routine task to take photographs the

pictures to see for look for certain phenomena well that's what they expected

to see and this had been a picture of this region of the sky taken prior to

this night but on this night when they developed their photo place they saw

something like this though to their great amazement there was an extremely

bright star in their field of view and bars are not supposed to do that

you know planets move around the sky you know the moon moves and wrote in the

rotates and in phase so that it shows the same phase to us our stars are the

vast majority of the time perfectly stationary and the fact that the very bright star would appear in this region

was a course surprising they went outside and looked at the sky and there

it was you could see it within with a naked eye but of course you start that you can see

wherever the naked eye have to be very close this one was in a different galaxy so must have been very very bright

though the serendipity in this case as they they discovered a supernova

explosion by not going to sleep looking at the sky and so this gentleman all the

Ian Shelton is credited as a discoverer of this phenomenon which was last time

seen by Johannes Kepler a famous German astronomer and mathematician ah

who did this almost 400 years earlier when another super I went off and could be simple to make a

die but just to give you the reference on the time frame Kepler saw it before a

telescope was invented a few years before so he could not have taken a you

know a telescope and pointed at it but he did note this vocation well this is

amazing serendipity and obviously you know it would make a great Hollywood

movie but if you think about it what this means is that every night when most

sensible people go to sleep there are a few crazy people who look at the sky and

this is a truly amazing fact I think and they could be writing the next app and

getting rich and famous or they could be you know pursuing various other

interests they are fascinated by looking out at the universe though these people

will en was obviously a very lucky guy that night but perhaps not the only lucky person in this story there is a

whole team of people who got extremely lucky that night and this team of people has to do with with with this amazing

experiment that was going on at the same time deep on the ground in the mine in Japan so this this experiment comprised

of three hundred tons of very pure water surrounded by light sensor is called

photomultiplier was buried deep inside the kameoka mine in Japan and there was

a similar experiment of this type in the United States was called simply inb4 UC

Irvine Michigan and Brookhaven universities that may made up the team so these experiments both of them had

the similar characteristic they were doing a very strange thing they had a large volume of what of water with

absolutely nothing happening they're surrounded by for the multiplier tubes

and to make it worse it was buried the very deep inside mine though what they

were waiting for our tiny light flashes that would occur and this and this big

volume of of pure water and will they were built at that time to search for an amazing

prediction of a very exciting theory that took the world of political physics

by storm in 1970s four years ago and this theory

was which was called the sort of how should I say very you know the creators

of this theory were so impressed that they called it grand unification or guts grand unified theory this theory

proposed that all known forces of nature except for gravity so electromagnetism

strong and weak forces would be manifestation of the same fundamental interaction and therefore there was a

profound harmony to our universe and this theory was making a very important

prediction that protons would decay so protons which make up without

fundamental ingredients of of matter were not eternal but they would decay of

course you know if they cannot decay too fast so the vast majority of them

survived since the beginning of the Big Bang but a very small fraction according

to this theory would decay and so the way to do that is to get a very large

number of protons in a very very quiet and isolated space pointed light detectors at this and and watch and this

was an experimental race that was happening and this was the reason why these detectors were were built but this

kamiokande detector came online in April of 1993 and the other detector IMD that

I mentioned came online a bit earlier in 82 and you know these guys test tasted

successful knows that this theory was so beautiful and it looks awesome you know

sort of elegant minimalistic and convincing that they thought that they would run the detector for a year and

they would see it well to their great disappointment they ran it and they

didn't see anything oh and of course the question is you build a fantastic

detector you wait you would like to do something else with it so what could they do though it was a

very profound and very smart suggestion

made at that time to use these detectors which were designed for proton decay to

look at something called the solar neutrino problem but now I make a little detour but it's time well spent I will

talk to you tell you about this song using a problem and how it's related to

the loo to to the the topic of my talk and super No well the first big

underground experiment the first experiment of this type was actually built 20 years before in 1960s and they

leave the result this experiment or rate Raymond Davis who is here and John pacol

who will provided theory support the apparatus for this experiment is sounded

with you know it's quite an odd apparatus if you think about it it had a

large volume a hundred thousand gallons of basically dry cleaning fluid though a

hundred thousand gallons that I mentioned here is about Olympic sized pool of fluid they put this detector

which was in this in this cylinder again

deep on the ground in South Dakota and they waited what did they wait for though what they waited for the

hypothesis that they were trying to test is that there were neutrinos coming from

the center of the Sun and these are three noes were produced in the Sun as

part of the solar energy generation so these neutrinos were supposedly produced

in the Sun escaping the Sun and then coming to earth going on the ground and

reacting in ray Davis's detector though these neutrinos were were expected to

cause a certain number of reactions basically alchemy reactions interacting

with chlorine nuclei in the detector and converting them to another type to

argon though John Bacall made the calculation and the prediction was that there should be 51 argon atoms converted

every month ray Davis when he started running his experiment he would

recirculate his detector and do it do the extraction of argon once every month

and he counted only 17 per month though there were indeed argon atoms made in

this detector in this giant Olympic sized tank of cleaning fluid but

unfortunately only one-third well if you

think about this this discrepancy persisted month after month year after year so in a you know very quickly this

is a very statistically significant signal and it existed you know

apparently this was an obvious statement in our face and we didn't know nobody

knew what to do with this so this came to be known as the solar neutrino problem the difference between the

predicted rate of argon atoms created by these ghostly elementary particles and

they observed rate now course you say

well then in science we know what to do there is a well-defined procedure of the

scientific method where you have a hypothesis then you test this hypothesis with

experiment and if your experiment the poor's the hypothesis and you reproduce

your experiment many times then this becomes accepted theory apparently this

was not the case or for these people so then of course the scientific method tells you that there is something wrong

either you have a flawed experiment or the hypothesis is incorrect and then you have to revise it though that's the

official way science is supposed to work that's the way I learned when I went to

the Science Museum with my kids but unfortunately in real life or

fortunately things are more interesting when you ask the Ray Davis whether his

experiment was flawed he said no and he had done many calibrations that is over the years to prove it and

then down the khole similarly analyzed solar model in many different ways and

came to the conclusion that it did not predict one third of the flux though here it was the problem that there was

no obvious flaw in either of these calculations yet the result was

obviously inconsistent though this was the Solon between the problem and how do you proceed well the way to proceed at

this point is to at least try to make this measurement and preferably with an entirely different detection technology

now come land already had a detector now you say well why didn't others jump on

the repeat Davis's experiment does it's a very difficult experiment well you basically you have to invest the maybe

10 or more years of your life to do something very very difficult you will do it only if you think the stakes are

high and you know you know where you can you know where something is if you think

that maybe there is a theoretical uncertainty for reluctant to spend 10 years of their lives portioned leave for

camera country they already had a detector and they wanted to apply this detector though in theory in practice

this detector was not ready to do this Solon is been a measurement and so they were required to perform a number of

very challenging technological upgrades but they needed the better water

purification system they needed better detection system electronics they needed

to instrument their their volume with something called the dito additional

sensors around the detector they did that and they completed troubleshooting

by January 2007 now of course you know why they got lucky because in February

2007 the supernova went off though when there was a news the news propagated

through the field that the supernova exploded in the Large Magellanic Cloud these new to the underground physicists

went back to their data and examined it and when they examined it they were completely thrilled because there were

in in in their detectors additional events that could be

triggered by something coming out of the supernova but there were 11 interactions

in the kamiokande experiment these interactions were closely spaced on time

in the 10-second window and interestingly there were two hours before the optical change was observed

in the in the same time window with these eleven events there were eight

interactions in the time window at the imb experiment and there was another experiment in the in the caucus

mountains of the Soviet Union likes and scintillated telescope which also saw five events though based on these 2000

events are I am going to make a claim that one hundred and sixty-six thousand

years ago in the neighboring galaxy a gravity power between the bomb exploded

in the centre of a dying massive star now this is the story how the we saw a

supernova is we knows I just have to explain my title do I have to say what gravity has to do with this and what our

nutri knows and why they are important for the explosion and they might have done so the first is gravity so gravity

as anybody who ever studied physics knows Newton's law of gravitation tells

us that the masses attract each other and this attraction is always on the

same force that pushes us down right now in this room makes us you know sit or

stand and not flow through the room with the same force that makes planets go around the Sun so the immediate question

is if you have a star which is a large amount of mass there is a force of

gravity that pushes on this material to compress so the question is why doesn't

this object class and if there was only gravity the star would collapse in

freefall and you can compute this time for our Sun it's about the aboutis order

a thousand seconds of freefall so there is nothing sticking the gravity

from collapsing this the material in the Sun would just fall to the center by the mutual attractive force though then a

very valid question is why doesn't this happen so obviously there is something that

counteracting this force very very precisely and this something is internal pressure of the gas now the situation is

known from everyday life think of a balloon so you have I have a balloon a balloon as surface tension mmm which

wants to the balloon to compress but if you have air trapped inside the balloon

the air will push out and the equilibrium will be established now the

harder the gas inside the more the pressure is that's an experimental fact

which you have seen in in many many cases for example if you if you drive a

car and you measure a tire pressure because of the friction tires get warmer you will actually measure a higher

pressure than on a cold day so the pressure pushing the gas in the case of

the Sun must be sufficiently high to on counteract this gravitational pressure of all of this mass well from this we

know that inside the Sun must have must be dense and hot and indeed the Sun is a

ball of very hot plasma and the pressure in the centre is about eleven million Kelvin temperature in the centre is 11

million Kelvin and the density is about 100 times the density of water so the

problem with this it's good that stars are balanced by this the problem is that

the Sun is a leaky balloon so what it leaks is not gas it's not that the gas

is coming out of the centre of the Sun but it leaks Heat well they heat the

energy of the gas that makes the molecules go around and push is constantly lost which is a great thing

because the Sun shines well we owe our existence to the fact that the Sun is a leaky balloon but unless there is a way

to replenish this heat the star would it's pressure and it would compress a

little bit then as it compresses a little bit that compression would raise the temperature and it would leak a bit

more heat than than it would compress and so forth well this object that though it doesn't collapse on the

timescale of 15 minutes it would collapse on the timescale of 30 million

years and this is just taking the gravitational binding energy of the Sun dividing it by the solar luminosity this

calculation was done by Kelvin also Helmholtz in the nineteenth centuries

great physicists of the nineteenth century they computed that the lifetime of the Sun would be only about 30

million years and they argued with Charles Darwin so Charles Darwin when he proposed the theory of the evolution the

theory of evolution he computed the rate with which you know natural selection

and evolution to take place and he got the hundreds of millions of years well

then these learned gentlemen told him we only have 30 million years though there

was a lot of trouble that the Charles Darwin had to go through and in his later writings he doesn't mention the

timescale of the evolution very much now it turns out Darwin was right and the

great physicists of the 19th century were not quite right even though older calculation was correct what they didn't

know is that there was an additional way to generate energy there was a way to replenish the energy of the in the

center of the Sun and that was nuclear reactions now this is the this is 20th century physics so there are you know

steps done by many Giants of the 20th century physics and this is sort of a

very cartoon summary of it there was a discovery about a hundred years ago that

if you took four hydrogen nuclei these are you know atoms the hydrogen has an

atom with an electron and the nucleus but you would weigh this system you would weigh the mass of this nucleus and

then you would take a helium nucleus which made of two protons and two

neutrons and so you would observe ation was made that four hydrogen nuclei

wait a bit more slightly more than a helium nucleus now Albert Einstein by that time is a equals M c-squared law

was well known though it was realized that this mass difference could be converted to energy and actually Arthur

Eddington based on this observation made a suggestion that the Sun which was made

mostly of hydrogen and helium would be powered by converting hydrogen to helium slowly and this amount of power given

the amount of energy available in this process would take a long time for the Sun to do to sustain itself though there

are a number of brilliant physicists worked on this including people like George Gamow and Hans bethe and in the

end result is that by the end of 1930s the theory of stellar interiors and

energy generation was developed they they got a Nobel Prize for this and in 1960s this theory predicted that so long

as there are nuclear reactions in the Sun and they replenish the heat loss

through the surface gravitational collapses hold it and that's wonderful another really wonderful aspect of it is

that this process is a perfectly self-regulating if the Sun wants to contract and they raise the temperature

this speeds up the reactions the reactions are very sensitive to temperature which would produce

additional heat which would make the pore expand and which would keep things just so that the amount of energy is

equal to the amount of energy loss whether the evolution timescale for the

Sun is not how fast these reactions can occur but how fast the energy is lost so

Sun fortunately sits in this quasi equilibrium state this stationary state

for billions of years enough for a life to evolve and in the

world and so on so this is wonderful now for massive stars there is a similar

story only it turns out that if you go through modeling the stars are these stars are hotter and they evolve faster

so they burn they need more hydrogen burning and they run through their high

not in billions of years but perhaps in 10 or 15 million years and then what

happens gravity is always on right it's relentless it will not it will not take

a pause so what happens once one fuel is exhausted hydrogen the core will

contract as advertised now fortunately when it contracts conditions become right for the next

nuclear reactions that start though helium is burned into carbon which is

also good because in our world we know that carbon is very essential for life so in if you ask where it comes from

when BBM happened they were only hydrogen and helium well the you know

stars had to make the rest of the materials that we see but then if you're

if you want to push this further you can say well what happens as a carbon is exhausted so what you end up with four

massive stars is a structure of the star where you have so this sort of onion right you have hydrogen on the outside

it is burning into helium then there is a shell where helium burns into carbon and there is a carbon burning to neon

oxygen silicon finally in the center after all these consecutive stages and

iron core is formed though there is an onion and this onion takes about seven

and a half million years to form for 25 solar mass star now if you look on

Wikipedia how much energy is is available for binding elementary protons

and neutrons into a nucleus something interesting happens I apologize this is

the most technical slide of this presentation but bear with me well the idea here is that when you combine

hydrogen helium and so forth into more and more complicated things as the mass

of this nucleus increases the average binding energy of a given particle

nucleon and this nucleus also increases though it's advantageous in energy to

move this way these are more and more stable di that you encounter as you burn from

these elements to these elements you can generate energy that can hold the collapse but it turns out that it

doesn't go forever there is a turnover and heavy elements like uranium and so

forth are actually less energetically favorable the most energetically favorable element a nucleus is iron so

if you have these guys like uranium you know they want to beta decay so

basically you know nuclear energy and the atomic bombs work by taking this

energy and visioning these guys whereas a thermonuclear bomb and the and and the

things of that nature are tapping this energy here but as I mentioned in the

beginning the iron core is the most stable element and there is nothing less

to burn nothing else left to burn though when that happens and the core reaches a

certain magical number which I'm happy to explain maybe in the question and answer session all they can dress a car

limit is game over gravity finally wins there is nothing to all the collapse and this the central

region the core just three Falls just collapses onto itself well when this

collapse happens it's really dramatic it happens in a millisecond and then this free fall this material which is a

quarter of the speed of light so this is what this is basically the story of a big star what happens inside of it now

say I have this material it's collapsing through a very very dense state what

happens next well this is where the rest of the talk comes in oh the story I told you is

great and the question is how can you ever be sure I made statements about

things that are you know very very many light years away I cannot look inside

the core of this is hidden from us even if I make a theory for you for what happens next how

can we ever directly verify it and you think about it even if I am talking

about the Sun the first step that I told you that I'm burning hydrogen and hydrogen is converting into helium and

that's what's holding the Sun I cannot see that directly either right I mean

there are photons in this region but they don't travel out so there is no visible light coming out from the center

of the Sun so it's as if you have this guy and you would like to ask how big is

his heart you don't know all you see on the outside is a big fuzzy ball and you need

a way to look inside you need some kind of x-ray do x-rays is hard to see whether it's like this like this and

turns out in three noes provide this x-ray though the idea that was

motivating John Bacall and Ray Davis was to use neutrino particles to look in the

core of the Sun and measure the temperature and physical conditions there well this idea as far as I could

trace it in the literature goes back to the great physicist Bruno Pontecorvo and

occurs in his papers starting in 1946 and on through the 50s and 60s

Pontecorvo actually played the key role in many aspects of messina physics

he also defected to the Soviet Union from the Western 1950 and spent the

latter part of his career working in the intensity the nuclear research in Moscow oh that's mean this guy had a

fascinating life but anyway so there were these these suggestions that you

could look inside of their Sun the watering adrenals so neutrinos are you

know tiny elementary particles that have no electric charge and they don't

interact it was the strong interaction force that binds nuclei it was the neutrino was first proposed

in nineteen 30 by Wolfgang Cowley as a way to rescue

a problem that was baffling the physicists at that time they were measuring energies of positrons and

electrons coming from beta decays and these positrons had energies that could

not be accounted for unless there was something else to produce well some other particle was coming out the idea

of poly was to say that there is a particle it's a desperate remedy in his

opinion but at least something as fundamental as energy conservation is restored by the way there were big

debates whether the energy should be conserved in quantum mechanics at that time he said yes he was right and the

price for that was that he postulated that in these processes additional

particles came out when he made this suggestion Powell he said that he committed a great sin for a theorist he

predicted the particle that could never be discovered he called it a neutron but

it turned out in early 1930s no matter particle was discovered what we now call

the neutron though there was a problem with the name another great physicist

Enrico Fermi decided to call it a neutrino which in Italian meant a little

Neutron he also discovered the first theory of weak interactions which

produced which explained how many xenos are produced now for a while it was

thought you could never see the Agena no Hans bethe who I said was a giant of the

of the field at the time even wrote that there is practically no possible way to observe the athina not yet there were

very stubborn people who persevered and you know 25 years later succeeded well

Los Alamos scientists rather Aquinas and quite common set up a large detector

next to very close to a nuclear reactor at Savannah River and through devising a

clever technique did detecting in China why did we do it he explained because

everybody said you couldn't do it though sometimes science is driven by

sheer stubbornness and we're certainly glad that that he did you know fast forwarding to now reactor anti neutrino

experiments there is an experiment in China called the daya Bay and twin experiment sample of neutrinos is

300,000 neutrinos though right now you have very very very large experiments

measuring a lot of neutrinos back in 57 it was a feat to even senior t know once

now so this was in 57 so I'm you can put

a reactor next to a detector next to a nuclear reactor but what about 1987a

though the claim is that the Homestake neutrinos they expect the detector of

ray Davis which was at the Homestake mine in South Dakota was detecting its winners from the Sun which is eight

light minutes away but this this this exploding star as I told you is much much farther it's over a hundred

thousand light years away so if we are to see neutrinos from that source the

total number of emitted neutrinos has to be absolutely mind-boggling and then you can go through an exercise and compute

just how mind-boggling it has to be but you imagine that there is an explosion if winners are coming out in all

directions most of them miss the earth right they go in the sphere which spends a hundred

and sixty six thousand light years so a very small number of them reach the earth and Amanda those that reach the

earth most of them go right through the earth because the way in and Trina interacts if you somehow were able to

arrange water a Lightyear of water these winners could travel through this water

without scattering even once so a very small fraction of all neutrinos that

went through the detector is actually interacted and now we have 2,000 neutrinos so you can work you can take

this number and work backwards knowing their probability interact and the distance to the explosion you can infer

the total energy emitted in the engine knows if you go through this exercise which is not that hard

you will discover that the neutrino burst was actually a hundred times more powerful than the visible explosion and

the visible explosion I told you could be seen with the naked eye between the bursts in fact is so powerful that

during the ten seconds neutrinos are emitted the power in neutrinos is equal

to the power of all stars emitting light in our visible universe all stars and

the visible universe are matched by a single star by a single neutrino burst

from a single dying massive star but only for ten seconds now the

gravitational energy the energy providing this is the energy per gravity

of this collapsed core and you can put it in various units you can say that

it's ten to the twenty seven times greater than the most powerful from a nuclear weapon ever tested on earth and

those were horrible things that were tested on earth well ten to the twenty seven is ten to the twenty seven zeroes

though that a thousand trillion trillion times more powerful using more seriously

using again Einstein's relationship between mass and energy we can say that about tenth of the mass of the collapsed

core was converted into pure energy emitted and neutrinos the one neutrinos

left this collapsed core the object actually got the 10% lighter because of

this tremendous energy release well that's fascinating so this is if you

took the final object that forms in this collapse a neutron star and you

superimpose that on scales that we know so in superimposing this in the Bay Area with the center that's like it would

extend from about San Mateo to Cupertino but this round object would have more

mass than the entire Sun so because of such tremendous amount of mass

compressed such a small amount of such a small region of space a lot of energy is

released when it comes out in the bursts of neutrinos after neutrinos are emitted

and object cools depending on the details of the explosion you form something called

a neutron star which is basically a giant nucleus made of nuclear of of neutrons or maybe if it's a bit more

massive in a black hole so that the light can not even escape it's it's

gravity we don't know what happens in 1987a because we have not yet seen a pulsar that would correspond to the

neutron star well it's an open question the question is how the energy that was

liberated in this collapse was carried out and this is another important physics point that I would like to make

so you have a very very energetic system though I took this material I collapsed

it the collapse was halted when nuclei were pushed rise against each other the nuclear force finally pushes things

apart though the collapse is halted but there is a tremendous amount of energy

stored in this and it's carried out but by what the photons that are normally

carrying energy from the core of the Sun would take a very very long time because

this material in the collapsed core is a trillion ounces per cubic inch it's just

the so dense that a photon would scatter and would scatter again and would scatter many many times and it wouldn't

make it very far though turns out that the weaker your particle interacts the

better it is at carrying the energy neutrinos are also trapped as it turns out but not not as much they because

remember they are very very weakly interacting they bounce out they bounce

a certain number of times about a billion times but with this bouncing and

the size of the object which is about ten kilometers in radius they escape and only about ten seconds though this time

of diffusion of the neutrinos and seconds is exactly what sets the

duration of the bursts that was seen in 87 though

that's it in terms of energy diagram you

have a region of the central the central region on the star which collapses to

this object which fits on the map of the Bay Area a lot of energy is liberated

over 99% is emitted in 10 seconds and even the burst somehow the remaining 1%

is diverted into the visible explosion in terms of energy it's a tiny perturbation but in terms of

the universe as we know it is very very important it makes it takes the elements

that were produced in the center of the subject and throws them until outer space so a lot of things in this room

the gold and so forth were we think made somehow in the centers of the Sun of

these massive stars and expelled early on though this observation and the

observation of Solon gino's under 2002 Nobel Prize in Physics for pioneering

neutrino astronomy detection of cosmic neutrinos though Masatoshi Koshiba was

the leader of the chemical the experiment and ray Davis was the leader

of the South Dakota home state minister now and we do more than this though the

important thing is that people Nova explosions happen from time to time how

often in our galaxy is a subject of debate but estimates run from perhaps 30

to 50 years like major earthquakes and the Barry so

these are timescales that it does it happen tomorrow probably not is it the

worst to be prepared for the next one absolutely now I should make a parenthetical comments that some

supernova explosions have a different mechanism they are called type 1a they're extremely important for

cosmology they used to make measurements of dark energy I will not be talking

about these explosions because they produce fewer neutrinos point is that

there is this rate of events and this rate of events there is a good chance that the next one will be of this type

where core inside the massive star collapses and if we are to measure

neutrinos from that burst with more accuracy then we can really appear

inside the exploding region and the supernova well Ocean Utley it just

happens that there are new bigger more

accurate and the ground detectors in the work and particularly in the u.s. there

is a development called the deep underground neutrino experiment or doom it is going to be located in the same

mind in South Dakota where Ray Davis did his experiment and it will involve a lot of material it will involve a hundred

thousand tons of pure liquid argon and at the day it will be equipped much

better than the old detectors of the of the 1980s this is a big international

collaboration and the total cost of this project is going to be a billion dollars now you should be alarmed as a taxpayer

you are paying for it what for what is happening why is this being big detector

being built though it turns out that there is the second part of the story remember the song Venus they were

missing two-thirds of them were missing turns out this was not an experimental mistake the theoretical prediction on

the number of neutrinos produced in the Sun were correct some of these neutrinos were transformed on their way out of the

Sun into another type and this discovery which has been recently confirmed by

several experiments is the biggest discovery in particle physics in the last several decades or one of the

biggest discoveries though these people did not make a mistake instead they had

a discovery so it turns out that there are several materials several types just

like there are several types of electron

type particles so in addition to the Tron there is another particle called the muon and another particle called the

Tau leptin they have the same interactions as an electron but they're

more massive so they are created for some time then they decay to an electron and and other particles the Tau lepton

by the way was discovered here at SLAC first time and the Martin Perl got a

Nobel Prize for this discovery in 1995 the point is that each of these guys has its own siblings of antennas and these

are these neutrinos are called different flavors of neutrinos it turns out with if they have a nonzero mass they can

transform into each other in flight and that was happening in the Sun though

there were several experiments built tends to test the soloing between the problem and conclusive measurement came

from this detector in the set very mine in cam in in Canada

the idea there was that you have different ways of measuring neutrinos

and some ways would detect all three flavors all three types when this

measurement was done for all three types the total flux was exactly as the solar

model predicted and the reason why Bray Davis was measuring one-third of this

flux is because his detector was sensing to only one type called the electron

regime oscillations were also confirmed in other experiments so this this

anaconda detector that I showed that was fortunate enough to see the supernova

neutrino burst was superseded by a bigger detector called super-kamiokande

which was much bigger 50 times bigger in volume it measured neutrinos produced in

the atmosphere as a function of the direction and so unambiguously that depending upon how far neutrinos travel

they change from one flavor to another and the both of these experiments earned

the Nobel Prize in Physics this past year so this is the price

was given in October a few months ago though the the solingchina problem was

not a problem it was a discovery but it took of course a long time to devise other Paramount's to prove this and

ambiguous now what is this billion-dollar experiment doing the one that I described this billion-dollar

experiment is going to create neutrinos in the suburb of Chicago at the

laboratory called formula is going to shoot these neutrinos to the to a giant fire detector in South Dakota and the

the way neutrinos oscillate from one flavor to another will be measured extremely precisely there are thoughts

that by measuring it precisely maybe we will learn additional things about our

universe how there are theories how matter antimatter asymmetry is created

in the universe why there is more matter than antimatter and maybe neutrinos hold

the clue maybe there is something totally unexpected in this measurement anyway we know that neutrinos oscillate

and there will be a next next generation precision the experiment to measure the

measure this process now this detector is perfect to measure supernova

neutrinos it's not built for the sole purpose of waiting for the next supernova it has a daytime job but once

it's there it can do other things one thing it can do it can look for proton

decay remember I told you that protons were not found to decay in the first

experiment now we would like to know if they decay but just on the longer timescale and of course while this

experiment is doing it's a daytime job it will be waiting for the next supernova when the next supernova birth

comes instead of two dozen events we expect many many thousand events so you

will be able to measure to observe between inspector you know second-by-second to see what happens in

this object and how it evolves which will really provide a window inside the subject what will we learn

how the explosion develops as I already said the way the explosion is launched

is still an open question there are efforts to model this process which is

extremely complicated on the world's largest supercomputers and this will be

a way to look inside that animal directly you see Beckham by second what

happens in the explosion it will also tell us about matter that compressed to

the super dense object how it behaves when it's compressed to such densities notice that there is nothing that you

can do in the lab compares matter to similar densities so this experiment is

outside of what is possible in our control the environments in the lab how

neutrinos oscillate under these conditions again this is an experiment

that you can only do in the sky and last but not least whether there are other

particles even less interacting than neutrinos that are showing up in the

supernova and perhaps pulling it faster than what things we know is a long wood

though there is a long long list of physics questions sometimes in the next

several decades there will be an explosion in our somewhere in our galaxy we don't know when but we know that for

10 seconds there will be enormous burst of neutrinos and there will be no warning for this burst though this

detector which is being designed now better be designed right though that you know 20 or 30 years from now it can get

the most physics out of this signal and that's all I want to say that's why many

of us are quite excited about about studying for novel explosions and what

neutrinos should come out of them they're Methodists what to know what would like to know how they design their

detector though that they can and can get a look inside the some of the most

powerful explosion in there in the universe no that's thank you I just want to close

with this picture Oh John Bacall was not only a great physicist who was central

to the neutrino physics but he was actually remembered fondly by many of us

as a great mentor he was a he certainly

taught me a lot and he it was a had great fun teaching young scientists and

so now we just have to carry on this and now if you can recognize this guy he is a slightly younger version of what you

see in front of you here anyway um thank you and if there are new

questions go ahead okay so we've seen

that Alex can comprehend explosions as

powerful as all the stars in the universe so any questions the the procedure for

the questions is the following um will call on you make sure you have the microphone in your hand before you

ask the question so the question can be on the video that's being made of this lecture so sorry you can have the first

one bring them the microphone please yes so my question is this the core where

are you know okay when the core is

collapsing you have this outburst at last ten seconds but as the on the other

slide you show that combining two hydrogen atoms in you get a helium atom

and then the positron in the new Trina but it seems unrelated to the collapse

of the core it seems like the the new Trina that get emitted during these ten seconds already exists inside the core

they're not actually generated because the helium in the night and the hydrogen

are actually on the surface of of this I'm glad you're asking this because it gives me an option to clarify something

that I don't I don't want any possibility of that confusion so the

neutrinos that come from nuclear reactions allow you to look at the stage of stellar evolution when they're

burning lighter elements to heavier element this is what we're doing in the case of the Sun right we're looking at

neutrinos that come there and they tell us that hydrogen is slowly being turned into helium when the massive star dies

it's when this all this process went through its full task to to iron you

have an iron core there is nothing left to burn so you know the fuel tank is empty the car ran out

of fuel though then gravity says aha at last though then it just it wins and it

collapses when it collapses it's a very dense and and hot object well the

conditions are such that neutrinos can be created by just interactions that

other particles moving around the same way that photons can be created when charged particles bounce around normally

we don't think that it's important because neutrinos are weakly interacting if I take something and I shake it

I don't emit neutrinos however these are so these conditions are so extreme that

neutrinos are created not by nuclear reactions so this is the important clarification but by other physics by

particles colliding with each other electrons turning into protons toriel

electrons turn and neutrons turning into protons and so forth now when they are created they're

trapped which is insane because that's the only place about in the universe where they are trapped but they they go

through a Lightyear of water but their density is so high the death trap

what trapped means that they bounce around and after about a billion bounces

they get to the surface and they escape so that's the story oh yeah the Solar

story is analogous in a way that it provides you a way to look inside but

the way the neutrino produced inside the supernova the physics of production is different you're absolutely right to

note thank you much um my question is um

could you explain a little about the change with Fay Cawley limit there we go

this is one of those cases where a wizard is not supposed to use magic but

I will in say mask though it turns out

that there is another way in nature to counteract pressure other than thermal weight and that other way is formally

called the electron suppression sorry about this name the

idea is that if you take a lot of electrons and you push them in the same region of space they don't like to be

there so this is called the Pauli exclusion principle and it's why chemistry exists that you have you know

electrons taking up different orbitals inside the nucleus they don't want to be

on top of each other Pauli told us that they're not allowed to be together when you push an object together an object

like our Sun eventually will be halted by this pressure and our Sun will end up

as a white dwarf the white dwarf is an object that you know went through several stages of burning but it has

electron pressure that keeps it from collapsing it's great because this

object can just sit there forever and that's why white dwarfs sit there they slowly cool but they don't need to

collapse turns out that if you put enough material in this object the

electrons trapped in this space become relativistic and then another set of

great scientists told us that in this case that the pushing force is not

enough so when the object becomes more and more massive eventually the penalty

for that you get by compressing it more the energy released and gravity is not

compensated by increased pressure of electrons and that's what happens

actually when the iron core collapses it also happens when a white dwarf accretes

mass from other stars for example a companion and when it reaches one point

four solar masses it goes up and that one is called the typ type 1a supernova which I promise not to talk about but

the point is that you know there is another mechanism other than heat to keep to keep gravity in check but it

only works unless until the object becomes sufficiently massive now one point for solar masses happens it's a

magic of our universe it's the combination of Newton's and the proton mass it's a combination

of very basic properties in our universe why they have to come up to one point

for solar mass is magic but it is of the

stars that are massive enough to produce a neutrino bomb supernova there are any

characteristics of the light or any signals that you can pick up from these stars to allow you to focus on ones that

are more likely to go supernova soon do they give off like into the same kind of

information that that it may be geologists use to predict on earthquake that's about to happen there are

discussions there are stars that we know are in their late stages so when they're

in the late stages on the outside they start losing material there are certain

telltale signs the problem is that it will explode soon means it could explode

in the next 20 thousand years not soon by the stellar timescales but not enough

for us it is actually one you know a very cool idea that these stars before

they collapse they are already meeting in Venus from the energy losses in their

course these are called pre supernova neutrinos and they should be emitted one

or two days before the color impending collapse there is another type of

detector that I didn't talk about that is being planned in Japan of the hyper kamiokande detector they already had

super so next is hyper even more water and that detector it is thought if it's

built correctly within principle detect such pre supernova neutrinos if the supernova happens to be close enough so

it happens on the other side of the galaxy no but if it's close like Kepler within you know two kiloparsecs from us

perhaps though when I said that there will be no warning it's a slightly

simplifying statement we may get lucky and there may be a neutrino warning too in between the bomb the neutrinos coming

from these life stages are actually very in late stages of evolution are very important I flashed the diagram which I

didn't discuss very much but there is something very cool happening in this onion picture no this guy is fantastic I

love him though the onion picture right though the onion shows how long it takes

for different elements to burn though I said that hydrogen burns seven million

years but notice that the light stages take only a day now I said that the rate

with which stellar evolution proceeds is not by how quickly things could merge but by how quickly energy is carried out

though you know it's like if you have a balloon it has a hole you want to keep

it steady so you keep blowing how much do you blow as much as escapes through the hole though it turns out

that in these late stages neutrinos coming from the center become important

they are the ones that carry energy and well then you have to burn faster so instead of burning for millions of years

these last stages only take months and then days and so right so well there is

something very important happening at the very center of the Sun all of this lots the Sun this massive star but we

will not know until and unless we look with neutrinos inside on the outside it

looks like a star could be twenty thousand years before explosion hi

I use it something about the formation of neutrinos during the star collapse that I'm not sure I caught correctly

okay you said that during the collapse of the star all the neutrinos were formed of one of the three flavors and

that some of them changed into the other two flavors on their way out oh I'm glad I'm getting these fantastic questions

when you make a public talk there are a lot of things that the you hope the audience will ask that you can't explain

and do so it turns out that when you have nuclear reactions in the center of

the Sun you only make one flavor of meeting nuts because you own

they make electrons or positrons and in part of your reactions though let me

take you back to where is death oh yeah and this guy is now there so now

I have two protons they merge one of them becomes a neutron there is a positron which is emitted to compensate

charge right so there was the word charge to here though something positive had to come out and then there is a

neutrino this neutrino is the brother of this positron so it's of an electron

type doesn't say here but this is electron that means we know we can say well what about the other guys can I be

made a muon the muon turns out to be too heavy there is not enough energy in this

burning process only a few MeV and the muon is over 100 we just can't make

muons and Tau's the only electron neutrinos are produced then you'll let them fly for eight minutes to us and

then somewhere in this path they get converted into the other one so that's the Solar in between a problem and

solution we started with only one type because of nuclear reactions and not enough energy and you ended up with

three by just this magical phenomenon called oscillation in the supernova the

conditions are so energetic that you can produce all three types we can produce

tau muon and electron already there at the source just because there are many

more is much more energy available for it for that they still have different

spectra because they interact differently and this is a more subtle question the magician here the wizard is

really tempted to use some magic and start writing equations so they are more

energetic but they have different spectra and what comes is some permutation as they further oscillate

into each other though by disentangling this isolation from the signal that you observe you can

learn a lot about the physical conditions in this in this explosion but that's beyond the scope of

a public lecture so ask me offline I saw

on one of your slides that there was about a 10 minute delay between the neutrino signal and the optical signal a

lot of jars if you make up at a significant delay yeah and I was wondering whether that was due to the

relatively weak scattering of the neutrinos meaning they were more rapidly well this is great too right this is

great to discuss that so what happens is the following you have this central region which emits a giant burst of

neutrinos and somehow as bipro is a byproduct of this process there is a short wave with 1% of the total energy

that goes through the rest of the star and disrupts it how long does it take for the short wave to get to the surface

two hours right though something happens in the center between us come out and

you see them immediately right because this is a message from the center and then there is some complicated

hydrodynamics which takes place where this the explosion travels through the

star disrupts it and then on the outside at some point you see oh there was an

explosion and it got out though that's the delay it takes to get out if you

have and then this next generation of telescopes and there is a way to roughly

pinpoint the direction from which neutrinos are coming from you can use that to tell astronomers where to look a

clarification question regarding that argon arm in a pool what kind of

permutation do you expect of are going to go through and the second question is a dry cleaning fluid dry and fluid right

cleaning fluid it's a molecule of two carbon and for chlorine okay that's the

it's a chemical compound okay that is commonly used as a dry cleaning fluid so therefore it was available it wasn't

some exotic thing okay the doones right it was not clear exactly in fluid it's what you would use to take your you know

clothes cleaned the same one that was that's why it's dry cleaning okay good

it's a t2 chlorine for Hawaii it was chosen because it has a lot of chlorine

and chlorine nucleus had this property that it could react with an electron

neutrino coming from the center of the Sun and the one ingredient inside of it

put flip right so in an electron neutrino would become an electron

negatively charged one neutron inside of this guy would dip become a proton but

you know then it becomes a different chemical element it turns out that the next this element it becomes this argon

argon is great because it's inert so it doesn't react so you have hope of

extracting it you still have to do fantastic chemistry but you have a way of extracting that that argon and in the

case of radius ki was extracting 17 atoms bargain because if it was

something that was strongly reacting you know it gets attached to something else and then good luck pulling it out so

chlorine is one step away from Arden though that that's why it was chosen and it had right properties or a neutrino

interactions yeah so a couple weeks ago

I was at a meeting with a fella named Mark Messier who's one of the experimenters working on this June

project and someone asked him what neutrino detectors are made of and he

went into some long spiel and then he said neutrino detectors they're so huge they have to be made of stuff that's

extremely cheap and so that's what it is cleaning fluid plastic big sheets of

iron um that's the stuff that you have to work with to build detectors at this

scale okay why don't we take two more questions so this one here one question

was respect to the speed of travel of the neutrinos the timing of events seems

to imply they are traveling clothes or at the speed of light given that they have even a little tiny

mass is is there any relativistic effect no not at all of the neutrino I didn't plan these

questions let you know so there is an

effect if it's a particle of a finite mass so it's traveling at the speed of light but not exactly and the question

is can we ever know right though because there is no other reference to say there

was a zero of the explosion it's not clear when the new Trina comes to you

that it was delayed by a some amount however it turns out that the exact

arrival in that case depends on the entry no energy more energetic guys they still travel faster because for them

matter mass relatively speaking means less right though if you have a pulse of

neutrinos where there is some a very strange pattern that more energetic guys

arrive first and then they become less energetic this would suggest that this

dispersion effect the difference of speeds is what you are observing though for poorer

from 1987a we know that this this separation between different energies

could not have been longer than ten seconds that provides a bound on the convenient mass about twenty electron

volts if you are interested it's not the best bound we have but it is you know a

bound from the next supernova we think one electron volt is plausible against

not the best but it's close to what you are getting now from the best Rest

really experiment and that's that will

be one of the scientific byproducts of the next supernova you will know how if

between a mass is a one electron volt or or more you will see it in your in your

distribution of neutrino energy

hi also about the speed so it seems that the neutrino is travelling very close to

speed of light and a couple years ago we refuted a claim that it was travelling faster probably experimental error but

do we have a good mechanism for why it's travelling at speed of light we know photons go this way because the characteristic stiffness of the E and

the B field or magnetic electric constants yes we think that based on the

laws of relativity of Einstein any particle with a zero mass has to travel

with the speed of light and it's the same speed of light for all massless particles and all particles we have now

finite masses have to deviate from the speed of light in the same prescribed

manner in the vacuum if this was not so

and you could use one particle send the signal in the past of the other particles things would get very

complicated very quickly so Einsteins postulate that the speed of light was

exactly the same and all the reference frames actually applies not just light not just photons but any kind of

massless particle that exists in nature it was thought that madrenas travelled literally with the speed of light now we

know it's very very close but technically not exactly the speed of light and the fact that they are

oscillating it's because it's not at the speed of light so you can go to the frame where they are at rest and when

you look at them in that frame something happens you can catch up with the neutrino and you can look at the news we

know but there is time for it to happen that was moving at exactly the speed of light you could catch up with you could

not catch up with this neutrino so it couldn't undergo changes on the flight

hey we we're done so so very so then

it's like Alex

SLAC National Accelerator Laboratory