But the most important thing is that the star's form bigger and bigger chemical elements.
The sun burns hydrogen to build helium. That can happen even
in a very smallish star, like the sun, the hydrogen can
go to helium. In the
case of the sun, it can probably go all
the way up to carbon it will bring in three helium nuclei together fuse them
into carbon. That is
going to happen in the sun as well after it comes very close to the end of its life when it runs out of the hydrogen fuel. But it’s believed
it doesn't go any beyond that. We need much bigger
and more massive stars to let the reaction go further. By going from carbon
to neon and silicon
and iron we can keep building up heavier and bigger elements by
using the inner core of bigger stars. If you take some example
of a typical star which goes all the way down
to iron, the time scale is actually not that long.
Hydrogen burning may last like only like seven
million years. Then things start to get
faster and faster, helium burning into carbon, to neon, oxygen,
silicon. At the end of the day, silicon burning may last only
one day and then comes to a dead end. Once it comes all the way to iron, it cannot go any further beyond that. That’s simply based on energy
conservation. If we want to go beyond iron,
then instead of
releasing energy, by shedding mass, we need to put energy
in to make the reaction happen. So that doesn't happen
inside the sun or any
stars as far as we are concerned. So this is a dead end.
Once it comes to iron core then it cannot do any more nuclear
fusion process to release more energy to
support its weight. Then it would collapse. That would
lead to an explosion of the star. This explosion
also caused lot of nucleus
to come out. Even
though this is a very, very big explosion, we
could see by naked eye that this explosion emits
light almost comparable
to the entire galaxy of Large Magellanic Cloud.
Actually, 99% of energy
is released in the form of neutrinos. Only 1% is
something you'll observe in terms of light. So tons of neutrinos
are released and after the travel of 160,000 years, they reach another water tank, or that happened in
1987. So this burst of neutrinos came from the explosion of this supernova.
But more importantly from this observation even this distant star that has
exploded 160,000 light years away is also made
of atoms. This
star has been putting these atoms together
to build up heavier and bigger elements all along.
contd...
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