0:08 so what happens during the lifecycle of
0:13 a star some B movies an Oscar a star on
0:14 the Hollywood Walk of Fame
0:17 no that's a different kind of star
0:21 I mean stars found in space like our Sun
0:24 All Stars initially form from a cloud of
0:28 dust and hydrogen gas this cloud is
0:32 called a stellar nebula gravity over
0:35 millions of years causes the dust and
0:37 gas to spiral together the particles
0:39 move faster and eventually reach
0:42 temperatures of millions of degrees to
0:46 form a protostar a star forms when it is
0:49 hot enough for hydrogen nuclei to fuse
0:52 to form helium for more about nuclear
0:57 fusion watch this video the star then
0:59 enters a long stable period where the
1:01 outward pressure of the heat generated
1:04 by nuclear fusion counteracts the force
1:07 of gravity the star is now called a
1:10 main-sequence star and it stays in this
1:12 state for between 10 million and 10
1:16 billion years what happens next depends
1:19 on the size of the star let's talk about
1:21 a smaller star first one roughly the
1:26 size of our Sun up until now the nuclear
1:27 fusion has been occurring between
1:30 hydrogen nuclei but eventually the
1:33 hydrogen begins to run out now the
1:35 outward force of fusion is less than the
1:39 inward force of gravity this causes the
1:41 star to collapse inward and the
1:44 temperature to increase it becomes so
1:47 hot that helium nuclei can now begin to
1:50 fuse together to form heavier elements
1:54 but only as far as iron to form elements
1:55 heavier than iron
1:58 requires an input of energy which we'll
1:59 explain a little later
2:02 the star now expands and becomes what is
2:06 called a red giant when our Sun becomes
2:08 a red giant it will expand to such a
2:10 size as to engulf the three inner planets
2:12 planets
2:15 next fusion of helium in the red giant
2:18 will eventually stop suddenly the force
2:20 of gravity is greater than the outward
2:23 pressure of fusion causing the star to collapse
2:23 collapse
2:27 forming a white dwarf no more fusion is
2:29 occurring inside the star and so the
2:33 white dwarf cools down eventually after
2:36 many billions of years of cooling it
2:38 stops releasing Heat and it becomes a
2:41 black dwarf as cold as the empty space
2:47 that surrounds it so what about bigger
2:50 stars what happens to them they follow a
2:52 different pattern these stars to
2:54 eventually run out of hydrogen but
2:57 quicker than a smaller star would
2:59 massive stars as a result have a much
3:02 shorter main-sequence life than smaller
3:06 stars these stars then expand to become
3:09 super red giants now full of all the
3:13 elements up to iron eventually fusion
3:15 stops resulting in the collapse of the
3:18 super red giant the shock wave created
3:21 triggers an explosion a supernova
3:24 producing a lot of energy in the form of
3:27 heat and light which can outshine all
3:29 the other stars in the galaxy for
3:31 several weeks the extremely high
3:33 temperature and pressure that exists
3:36 inside a supernova enables the fusion
3:39 process to create all of the elements in
3:40 the periodic table
3:44 that's a heavier than iron the supernova
3:45 distributes these throughout the
3:48 universe so that means we're all made of
3:51 Stardust one of two things can happen
3:54 next either a neutron star or a black
3:57 hole is formed a neutron star is made of
4:00 densely packed neutrons formed when
4:02 under immense pressure electrons are
4:05 forced to merge with protons a black
4:07 hole is formed if the mass of the
4:10 neutron star is sufficiently high to
4:12 cause further gravitational collapse a
4:15 black hole has such strong gravity that
4:19 even light cannot escape it we cannot
4:21 yet observe a black hole directly but we
4:24 can detect it by the effects it has on
4:25 nearby objects
4:28 such as stars now that's one
4:32 star-studded lifecycle if you liked the
4:33 video give it a thumbs up and don't
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