all the elements that are heavier than
ion like the golden platinum in your
jewelry the barium used in green
fireworks and the lead used in your car
batteries they were all created by
nuclear fusion reactions in a fraction
of a second during a super NOA
explosion or are they the story is
almost correct except for these elements
are not really created by nuclear fusion
reactions and they're mostly not created
in super noi when I first learned that
this was a huge misconception that I had
I got so many questions like why do we
say that these heavier than ion are not
created by nuclear fusion reactions and
if not by nuclear fusion how are they
created and if not in superi where are
they created and most importantly how do
we know about all this stuff oh my God
so many questions and I had no answers
to all of them until I met Margaret
Burbridge and then my mind was truly
Brown so the goal of this video is not
just to learn but like always to
ReDiscover where and how exactly are
these elements that make up your jewelry
or fireworks how are these elements
heavier than ion actually created so if
you're ready for this let's begin let's
back up a little bit we all know about
the incredibly beautiful but also
incomplete story about how the elements
are made it goes something like this the
hydrogen and the helium were made in the
Big Bang and all the other elements were
manufactured in the stars by the way you
keep asking me where I get my t-shirts
well I've started making my own and now
you can buy them as well okay stars are
powered by nuclear fusion reactions you
probably know this right because when
lighter nuclei fuse together the heavier
nuclei are more tight bound as a result
they release energy and the Stars use
that energy to you know counteract
Against Gravity so if you could Peak
inside the core of a very massive star
you will actually find shells of heavier
and heavier Elements which are being
forged by nuclear fusion reaction but
that is only until we get an ion core it
is one of the most tightly bound nucleus
in the universe so if you try to fuse
ion together it will not release energy
you require energy and therefore Fusion
stops and that's why you can only use
nuclear fusion to produce elements up to
ion and now because there's no longer
Fusion there's no longer a power source
gravity vins and the core starts
shrinking and because of the extreme
pressure generated inside the core the
electrons actually fuse with protons to
create a neutron star this is one of the
densest things in the universe and now
the collapsing shell bounces off against
this neutron star sending a shock wave
producing a supernova explosion and the
story usually ends with one last
sentence which says that all the other
elements in the periodic table are
created in a fraction of a second during
this super NOA explosion and it's this
last sentence that we really want to
pick apart in this video and to do that
we're going to talk to who is she you
ask oh you know just a regular badass
astronomer I mean she was incredibly
influential in a field that was
completely dominated by men during that
time not only that when she was awarded
a prestigious astronomy award which was
exclusively reserved for women she
rejected it because gender
discrimination and most importantly she
she co-authored one of the most
influential one of the most argu
arguably the most important paper ever
written in astronomy the b square FH
paper so Market why are elements heavier
than ion cannot be created by nuclear
fusion reactions I mean I understand
that fusing these elements will not
release energy they will you know
they're endothermic reaction they absorb
energy but we we're talking about
Supernova explosion there's so much
plenty of energy over there so surely
this must be happening right and
Margaret says Mahesh fusing such heavier
elements require hundreds of billions of
Kelvin to overcome the kum's barrier and
I'm like I get it but
Supernova and she's like that's not the
point do you have any idea how much
energy photons would have at such
temperature and I'm like no but why are
we talking about energy of the photons
and marget says well you can easily
calculate that just by using bolman's
equation right like KB into T um where
KB is the bolman's constant and T is
absolute temperature in in Kelvin
temperature in Kelvin okay so if you
just plug in the numbers you would find
that the average energy of the photons
at such high temperatures of hundreds of
billions of kin would be about 10 to 20
Mega electron Vol and I'm like okay but
why should I care about that because
this is The Binding energy of all the
nuclei in other words a photon with this
much energy can actually rip apart a
nucleus so Margaret what you're saying
is if you want to fuse heavy nuclei the
temperatures required are so high
hundreds of billions of Kelvin that even
if we do achieve that temperature the
photons over there would be so energetic
they would actually rip the nucleus
apart and Margaret is that that's yeah
exactly and that's why you cannot have
nuclear fusion of heavier elements this
is called photo disintegration and I'm
like oh my God I never really thought
about this so Margaret it looks like
it's going to be hard for nature to
start creating heavier than iron
elements isn't it and Margaret says
actually mes it's going to be super easy
bar in inconvenience I'm like how use
neutrons during a supernova a lot of
neutrons are created some of them come
from the photo disintegration at such
high temperatures we spoke about others
can come because you have a neutron star
at the core of a supernova right so when
something bounces off of it a lot of
neutrons get splattered off and so these
heavy nuclei like ion for example can
start capturing a lot of neutrons and
that's how it can start creating heavier
and heavier elements and I'm like
Margaret wait a second capturing
neutrons does not produce new heavier
elements they just produce the new
isotopes of the same elements right well
marget reminds us that mahes true but
when you capture a lot of neutrons like
what happens in a supern noi nuclei
tends to get unstable too many neutrons
make a nuclei unstable remember that
we've talked about that in detail you
know as to why that happens in a
previous video but just to summarize
just like electrons protons and neutrons
inside the nucleus also have energy
levels and they fill it kind of like the
electrons do and so if you have too many
neutrons look the energy level of the
entire nucleus becomes too high and so
what the nucleus what happens now is
that some of these neutrons will get
converted to protons so that the energy
overall energy can be reduced and the
whole thing becomes much more stable
than before this is called the beta
Decay it's called so because in this
conversion beta particles like electrons
are created and even neutros are created
which I haven't shown over here because
that's besides the point also because I
got a little lazy animating that but
long story short if you have too many
neutrons if you capture too many
neutrons well it becomes unstable and
some of those neutrons can be converted
into protons and that's how you can
create newer and heavier elements okay
so Market what you're saying is because
fusing heavier elements directly is not
possible because of the huge kums
barrier we get instead what happens is
they capture a lot of neutrons and then
convert some of the neutrons into
protons via better
Decay I find that hilar ious because
that's kind of like nature giving the
kum's barrier the
finger all right so we now have our
correct story all the elements that are
heavier than ion like the gold and the
platinum in your jewelry the barium used
in the green fireworks and the lead used
in your car batteries they were all
created by Neutron captures and then a
better DK in a supernova
explosion or is it so mahes now we know
that Neutron capture is the key to
creating heavier than IR elements right
so if you have a lot of neutrons flying
around more chances of the capture more
efficient this process becomes so superi
definitely creates a lot of neutrons and
back then we thought that super noi is
the only source of creating neutrons but
where else do you find a lot of neutrons
packed together neutron stars the core
of the neutron star is packed with
neutrons and the density is that of an
atomic nucleus the one of the densest
things in the universe besides black
holes depending on how you think about
density by the way but there is a thin
crust of heavy nuclei like ion and
nickel over here as well which can act
like seeds to capture these neutrons but
wait a second we need some kind of an
explosion to set this in motion isn't it
what kind of an explosion can do that
well what if you have two neutron stars
orbiting each other then they can lose
energy due to gravitational waves and
crash into each other and when that
happens of course they create a black
hole but a lot of neutrons are whipped
out and you have a lot of neutron flux
over here a perfect sight for an
efficient Neutron capture so today we
think that neutron star mergers they are
the dominant sites for creating such
heavier than ion elements in an
explosion but wait a second neutron star
mergers are way more rare compared to
supern noi because you need two neutron
stars orbiting each other right and yeah
they are but we believe that the
efficiency is so high that it
compensates for that but the big
question is do we have evidence for this
well certainly not during Margaret's
time because back then the concept of
neutron star was just being theorized
but today we do you probably know that
in 2017 Humanity for the very first time
detected gravitational waves from a
neutron star merger but what else
happened is we looked at the signature
the optical signature that you know that
comes during the neutron star merger and
from that we were able to actually see
we were able to detect heavier than ion
elements being formed in fact our
estimat showed that roughly about 10
Earth wors of gold and Platinum alone
were formed during that one you know
neutron star merger that must have
happened you know I think millions of
years ago so yes today we have proof
that it is indeed the neutron star
merger which is the dominant site for
creation of these heavier than iron
elements not superi neutron star mergers
okay so putting it all together we
finally have our story this means all
the elements heavier than ion like the
gold and the platinum in jewelry the
barium used in the green fireworks and
the lead used in your car batteries they
were all created by Neutron captures and
a subsequent bar Decay mostly in neutron
star
mergers or is it turns out that neutron
star mergers and the small contribution
that we get from superi they're
collectively responsible only for
creating about 50% of the Isotopes that
are heavier than ion so the big question
is what about the remaining 50% where do
they come from and again how do we know
over all of this stuff well to answer
that question Market says let's get into
the details of the neutron capture
that's happening during explosive events
like this so for example during a
neutron St merger let's say we have an
ion nucleus over here okay it is
capturing lots and lots of neutrons per
second very rapidly because there are so
many neutrons over there right in fact
the ion has become extremely unstable
right now and it wants to undergo a
better DK maybe it even does but it's
capturing neutrons at such a staggering
rate it just keeps accumulating neutrons
until it reaches a point where it can no
longer just hold neutrons anymore and
only once it reaches this point it'll
stop capturing neutrons and now it can
better Decay and convert those neutrons
into protons and eventually get to a
stable element and you can see now this
new new stable nucleus has a much higher
atomic number compared to ion because
there are so many more protons compared
to so many new protons compared to what
we had before right this is what we call
the r process rapid Neutron capture R
stands for Rapid over here
this is what must be happening in
explosive events like Neutron St mergers
and supern noi and the beautiful thing
about this is that we can even predict
what the end elements of the r process
would be where it would naturally end up
if we do the math which we're not going
to do it but if we do it turns out that
our processes should end in elements
like gold and platinum and other
elements like selenium for example so
these must be The Natural end points of
the art process theoretically now if
that is true then if you look up in the
sky then these elements which are the
natural end products of our process
these elements must be abundant right
because they should get
accumulated and so we looked up in the
sky and guess what that's exactly what
we found we found that elements like
gold platinum and selenium which are the
natural end products of our process they
are indeed more abundant compared to
their neighboring Isotopes and that was
a huge evidence in support of our
process in support of neutron capture
which is insane if you think about it
right but there was a problem we also
found some other elements to be abundant
compared to their neighbors which are
not the end products of our fres for
example berium and Lead they in fact
turns out that they get skipped over by
the r process so what's causing them to
get accumulated was the big question
what's going on over here Margaret
Margaret says to answer that question
she and her team can hypothesize that
there must be another way Neutron
capture must be happening one that's
happening much more slowly so that it
doesn't skip over any element for
example let's again start with ion and
let's say you capture now one Neutron
per month so you capture a neutron you
wait for a month if it's stable fine it
stays that way capture another one and
wait for a month if it wants to dek it
can Decay and now look the next element
can be formed and then you wait for
another month and see if you want to
capture another Neutron again if it's
stable it's stable and then if you want
to Decay well again you can Decay so you
can get the next element and maybe now
you'll get to the element like barium
and Lead what's special about barium and
Lead is that they have a neutron magic
number so just like how in noble gases
electrons are completely filled and so
they will not react with any element and
that's what makes them Noble and stable
turns out the same thing happens at a
nuclear level as well certain isotopes
of barium and Lead they have a neutron
shells which are compl completely filled
and as a result they will not accept any
more neutrons after that and so look in
this slow Neutron capture process barium
and lead and elements like these which
have Neutron magic numbers they tend to
be unnatural endpoints right and so if a
process like this happens then these
elements can build up so Margaret and
her team hypothesized that there must be
an S process as well s stands for slow
Neutron capture allowing enough time for
bet Decay to happen but the big question
now the final question now is where
exactly does s process happen I mean
clearly it cannot happen in explosive
EVS like neutron star mergers or supern
noi because that's there you get a rapid
flux where do you get one Neutron per
month where does this happen
Margaret turns out that there are
certain dying stars in which nuclear
reactions can produce neutrons and so
that would be a perfect site for the s
process but wait do you see how radical
this claim is I mean so far we used to
think that all the heavy elements were
produced in an explosion but now
Margaret and her team are challenging
that and saying ah about 50% of those
elements heavier than iron are produced
in a dying star not explosion but in a
star that is an extraordinary claim back
then and extraordinary claims need
extraordinary evidences so Margaret
what's the evidence for that and
Margaret asks Mahesh what do you think
what would be the evidence for finding s
process you know that s process indeed
happens in a star and I'm like oh I know
just point your telescopes at those
particular stars and see if you can find
spectral signatures of elements that are
created by S process like barium and
Lead if you see them then that's
evidence that they're over there that
that they're indeed present in the stars
and therefore they must be created over
there right and Market says not really
just because you find the elements in a
star doesn't necessarily mean they were
created there right it's possible that
those elements were created outside and
they found their way into the star just
like how all of the ion that is there in
the earth right now were created outside
of the earth and it's found its way into
the Earth right so just because you find
it over there doesn't mean you know it
was created over there I'm like okay
fine that doesn't work so then what do
we do look for radioactive isotopes that
have a very short halflife and I'm like
that is ingenious I mean if you detect a
radioactive isotope an isotope that only
has element that only has radioactive
isotopes with a short half life say for
example radium which is only half life
of, 1600 years then if it was created
outside then there's a very good chance
it would have decayed long before it has
any time to enter into the star so if
you detect radium inside the star you
know for sure that it was created in the
star amazing so all we have to do is
look for elements that have radioactive
only radioactive isotopes and short
half-lies that means we have to look for
elements above bismo that have very
short half lives right yeah the problem
though is that all the elements after
bismo can only be created in our process
because remember s process ends in lead
so that doesn't work oh no okay so this
means we need element which only has
radioactive isotopes which are heavier
than iron but lighter than lead and has
a relatively short halflife do we have
an element like that luckily we do we
have technum it doesn't have any stable
isotopes only radioactive isotopes it is
heavier than iron lighter than lead and
it's the maximum half life it has is
about 4 million years which is very
short compared to the life cycles of
these Stars which is hundreds of
millions of years so if we could detect
technum in stars that would be a strong
evidence of s process so it all boils
down to this trying to detect technici
in Stars so what happened did we detect
it yes we did in fact astronomer made
Paul mer just before his retirement
detected technum in those particular
stars and since then we have detected a
lot of technum stars so the fact that
we've seen technician being found in the
stars is a proof Beyond doubt that
indeed those elements were created in
the Stars themselves and therefore s
process is indeed a thing that happens
in these Stars this is how we know today
that about 50% of these elements heavier
than iron must be forged in those dying
Stars oh my
God putting together all this reasoning
and evidence and so much more Margaret
and her team wrote what some people call
the most important paper in astronomy
the b square FH paper it completely
revolutionized the way we think about
Stellar nucleo synthesis so now we can
put it all together you and me for one
last time you can say it with me all the
elements that are heavier than iron like
the gold and the platinum in your
jewelry the barium in your green
fireworks and the lead in your car
batteries the 50% of them are created by
the r process in neutron star mergers
and some of them in supern as well and
the remaining 50% of them are created by
this s process the slow Neutron capture
process in certain dying stars but I
guess the broader message over here is
that whatever we learn as facts about
this universe are actually conclusions
that scientists have made based on logic
reasoning and evidence and learning
about them is so much more richer than
just learning about the facts and one of
have a Merry Christmas and a Happy New
Year