Stars in space, like our Sun, undergo a lifecycle beginning with formation from nebulae, progressing through stable fusion stages, and culminating in different end-states based on their initial mass, ultimately contributing to the creation and distribution of elements in the universe.
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so what happens during the lifecycle of
a star some B movies an Oscar a star on
the Hollywood Walk of Fame
no that's a different kind of star
I mean stars found in space like our Sun
All Stars initially form from a cloud of
dust and hydrogen gas this cloud is
called a stellar nebula gravity over
millions of years causes the dust and
gas to spiral together the particles
move faster and eventually reach
temperatures of millions of degrees to
form a protostar a star forms when it is
hot enough for hydrogen nuclei to fuse
to form helium for more about nuclear
fusion watch this video the star then
enters a long stable period where the
outward pressure of the heat generated
by nuclear fusion counteracts the force
of gravity the star is now called a
main-sequence star and it stays in this
state for between 10 million and 10
billion years what happens next depends
on the size of the star let's talk about
a smaller star first one roughly the
size of our Sun up until now the nuclear
fusion has been occurring between
hydrogen nuclei but eventually the
hydrogen begins to run out now the
outward force of fusion is less than the
inward force of gravity this causes the
star to collapse inward and the
temperature to increase it becomes so
hot that helium nuclei can now begin to
fuse together to form heavier elements
but only as far as iron to form elements
heavier than iron
requires an input of energy which we'll
explain a little later
the star now expands and becomes what is
called a red giant when our Sun becomes
a red giant it will expand to such a
size as to engulf the three inner planets
planets
next fusion of helium in the red giant
will eventually stop suddenly the force
of gravity is greater than the outward
pressure of fusion causing the star to collapse
collapse
forming a white dwarf no more fusion is
occurring inside the star and so the
white dwarf cools down eventually after
many billions of years of cooling it
stops releasing Heat and it becomes a
black dwarf as cold as the empty space
that surrounds it so what about bigger
stars what happens to them they follow a
different pattern these stars to
eventually run out of hydrogen but
quicker than a smaller star would
massive stars as a result have a much
shorter main-sequence life than smaller
stars these stars then expand to become
super red giants now full of all the
elements up to iron eventually fusion
stops resulting in the collapse of the
super red giant the shock wave created
triggers an explosion a supernova
producing a lot of energy in the form of
heat and light which can outshine all
the other stars in the galaxy for
several weeks the extremely high
temperature and pressure that exists
inside a supernova enables the fusion
process to create all of the elements in
the periodic table
that's a heavier than iron the supernova
distributes these throughout the
universe so that means we're all made of
Stardust one of two things can happen
next either a neutron star or a black
hole is formed a neutron star is made of
densely packed neutrons formed when
under immense pressure electrons are
forced to merge with protons a black
hole is formed if the mass of the
neutron star is sufficiently high to
cause further gravitational collapse a
black hole has such strong gravity that
even light cannot escape it we cannot
yet observe a black hole directly but we
can detect it by the effects it has on
nearby objects
such as stars now that's one
star-studded lifecycle if you liked the
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