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Birth of Stars

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Birth of Stars

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let's imagine we have a huge cloud of hydrogen atoms floating in space.
when I say huge clouds-huge both in distance and in mass
when we combine those hydrogen atoms it will just be this really really massive thing
well we know that gravity will make the hydrogen atoms attracted to each other
and you normally don't think about the gravity of atoms, but it will slowly affect these atoms
as they slowing draw close to each other-as they slowly condense
they slowly move towards the centre of mass of all of the atoms
they slowly move in, and so if we fast forward,
these clouds will get denser and denser and the hydrogen
atoms are going to start to bump into each other, rubbing up with each other and interact with each other
denser and denser and denser
there is a huge mass of hydrogen atoms, so its temperature is going up
and they will keep condensing, and condensing, until something really interesting happens
let's imagine that they got really dense in the centre
and there is a bunch of hydrogen atoms all over, really dense
i can never really draw the actual amount of atoms here, just give you and idea
-there is a huge amount of inward pressure from gravity
everything wants to get to the centre of the mass of our entire cloud.
the temperature here is approaching 10 million Kelvin
and at that point something neat happen
let's remember what a hydrogen atom look like
i'm just gonna to focus on the hydrogen nucleus, which is a proton
if you want to think about a hydrogen,
it also have a electron orbiting around it
and let's draw another hydrogen atom over here
and this distance isn't to scale, and that isn't to scale either
the nucleus is acutally much much smaller than the actual radius of the atom
so we know from the columb forces, these electromagnetic forces
these 2 positively charged nucleus would not want to get near each other
but we do know that if they did get close to each other
under huge temperature and huge pressure,
and you were able to get the 2 close to each other
then all of sudden the strong force will overtake, it is much stronger than the columb forces
and these 2 hydrogens- their nucleus, will actually fuse together
that is what actually happens, once this gets hot and dense enough
and now we have enough temperature and enough pressure to overcome the columb forces
and bring the 2 protons close to each other
for fusion to occur- ignition
the reason why fusion-i want to be very clear here
the reason why it is not ignition and the reason why it is not combustion
- not like your normal burning carbon with oxygen together.
the reason why it is not combustion, and it is ignition
and the reason why it is called ignition, is that when 2 of the protons fuse
the resulting nucleus has a slightly smaller mass
and so the first stage of this, you actually have 2 protons
under enough pressure- obviously it will not happen
there is enough pressure and then the strong interaction actually keeps them together
one of these guys degrades into a neutron
and the resulting mass of the combined proton
is lower than the mass of each of the orginal proton
by a little bit-and this little bit results in a lot of energy
plus energy-and this energy
is why we call it ignition
and this energy provide with a bit of ourward pressure so that this thing dont keep collapsing
so once we get pressure enough, fusion occurs, and this energy provides
outward pressure to balance what is now a star
so now we actually have ignition at the centre
we have all the other molecules trying to get in
providing the pressure for this fusion-ignition
now, what is the hydrogen being fused into?
well the first step of the reaction
well I'm just doing the most basic kind of fusion that happens to stars
the hydrogen gets fused into deuterium
what is called heavy hydrogen
this is still hydrogen.
it has 1 neutron and 1 proton and is not a helium yet- it does not have 2 protons
and the deuterium keeps fusing and we eventually end up with helium
and you can see that on the periodic table
okay i have lost my periodic table i will show you in the next video
but we know that hydrogen in its atomic state has a atomic number of 1
and it also has a mass of 1
it has only 1 neucleon in its nucleus
but it is being fused, it goes into hydrogen 2, which is deuterium
which is 1 neutron 1 proton, which is 2 neucleons,
and that eventually
gets fused into helium - and im not going to go into that reaction
and by definition, helium has 2 protons and 2 neutrons
ok we are talking about helium 4 in particular- that isotope of helium- it has a atomic mass of 4
and this process will release a ton of energy
because the atomic mass of helium is slightly lower than
4 times the mass of each of the constitunent hydrogen
so all of its energy from the fusion under super high pressure and super high temperature to happen
keeps the star from collapsing
and once the star is in this stage,
once it is fusing hydrogen in its core into helium,
it is now in its main sequence
main sequence star
and that is actually where the sun is right now
and now there is question -
oh what if there just wasnt enough mass to get to this level
and there are actually things that cant quite reach the treshold to that level
there are are few things that dont quite fuse to this level so they dont quite generate the heat
or even smaller objects that just get to the point that there is just this huge temperature and pressure
but fusion is not actually occuring inside of the core
something like jupiter for example,
several mass of the gases
you will need to reach certain treshold of the mass
with the pressure and temperature so large
that you start with fusion
but the smaller you are above the treshold, the slower fusion will occur
but you are super massive, fusion will occur really really fast
so that is just a general idea of how stars form and why they generally dont collapse on themselves
and why they are this kind of balls of fusion reactions happening in the universe
and in the next few videos we will talk more about what happens
when the hydrogen fuel in the core starts to run out

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Birth of Stars

Birth of Stars