Stars: 19.2 Life Cycle of Stars With help from: l .
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Transcript of Stars: 19.2 Life Cycle of Stars With help from: l .
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Stars: 19.2
Life Cycle of StarsWith help from:
http://www.cosmos4kids.com/files/stars_develop.htm l
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A star is born
• Just like living organisms, stars have a life cycle.
• In the same way that you are born, develop, age and die, stars do the same things.
• One big difference is that stars don't need parents.
• Stars are born from huge clouds of gas and dust.
• It's amazing how that gas and dust are probably the most boring things in the universe and they can become everything.
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A star is born
• So you've got that huge cloud of dust and gas.
• Astronomers call that cloud a nebula.
• That's when it all starts to happen.
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Contractions
• The nebula begins to condense and form a ball.
• That ball is called a protostar.• "Proto" is a prefix that means "early" or
"before." • So a protostar is the first step in
becoming a full-fledged burning star.
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Start the Fire• After the star finished the protostar
phase, it becomes even denser. • The heavy elements move to the
center of the star while the light gases stay in the star's atmosphere.
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Start the Fire
• Those gases are usually hydrogen (H) and helium (He).
• Then something amazing happens, the nuclear fire begins.
• The star heats up and the gases ignite.
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Not all of them make it
• Remember Jupiter?• Jupiter is a special planet in that it
has a very similar makeup to the Sun.
• It has a low density and hydrogen and helium are the main components of the atmosphere.
• It is still missing one thing, nuclear fire.
• Jupiter could be the star that never was.
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This is a portion of the Eagle Nebula.
It is a birthplace of many stars.
The bright area is lit by young stars forming from clouds of hydrogen gas.
This picture was taken by NASA’s Hubble Space telescope (HST).
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Start the Fire
• Once nuclear fusion begins, a star is in the main sequence stage of its life
• If you looked, you would see the birth of the star.
• This is the longest and most stable part of a star’s life.
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Start the Fire
• The time a star will stay in this stage depends on its mass.
• The larger the mass - the shorter its life. This is because it uses up it’s gases much more quickly.
• Conversely, low-mass stars live longer.
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Path 1:Average Stars:
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Reaching Middle Age
• After the main sequence, an average - sized star becomes what astronomers call a red giant.
• This is the time when the star begins to die.
• As with anything in nature, stars need fuel.
• Well there is only so much hydrogen to fuel a star's fusion reactions.
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Reaching Middle Age
• Eventually that fuel runs out. • When the star begins to cool,
it grows. • The cooling takes the color of
the star and drops it into the red range, leaving a red giant.
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Betelgeuse (“beetle-juice”) is a red giant. It is located in the shoulder of the constellation Orion.You can see it without a telescope.
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Shrinking Away
• This red giant begins to lose some of its layers.
• Eventually it enters the Cepheid stage.
• This is the final phase of the star's life.
• It then becomes a white dwarf.• In a white dwarf, the core of the star
is left, some fires still burn, but there is very little fuel left.
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Shrinking Away
• It is about the size of Earth, but with the mass of the sun (whoa, major density here).
• Sadly, the white dwarf eventually goes out and becomes a brown or black dwarf.
• Our universe is not old enough to have any black dwarfs - or at least that we know of.
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This image shows the colorful "last hurrah" of a star like our Sun. The star is ending its life by casting off its outer layers of gas,
which formed a cocoon around the star's remaining core.The burned-out star, called a white dwarf, is the white dot in the
center.
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This is a picture of two stars: Sirius A & Sirius BThis is also an examples of a binary star.Sirius A is the brightest star in our sky. It is a blue-white Class A star.Sirius B is a white-dwarf.Sirius is part of the constellation Canis Major…Harry Potter Fans??? Notice something?
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Fire Works & Explosions
• If star is massive, it becomes a red supergiant instead of a red giant.
• When a supergiant starts to use up its fuel, there comes a point where the star's reactions stop and an explosion occurs.
• One day, BOOM! • That boom is the supernova. • Basically, this is the death of a HUGE
star by explosion.• Cool, huh?
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Way Cool Stuff
• Supernovas are awesome.• It is brighter than 10 billion stars put together.• A supernova can even be SO bright that it
outshines an entire galaxy for a few seconds.• More than 90% of a star’s mass is blown away in
this explosion.• Heavier elements like gold and uranium are
made as the atomic nuclei are smashed together.
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Supernova 1987A was discovered in 1987 and could be seen without a telescope.
You can see the difference before and after the explosion.
Today, it looks like a double ring.
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Losing Its Atmosphere• After that explosion, the supernova,
the atmosphere is blown away from the star.
• In the same way there was a nebula of gas and dust before the star was born, a new nebula is created from the explosion.
• Astronomers call the nebula after the explosion a planetary nebula.
• These are VERY cool looking
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Planetary Nebulas… what a star looks like after it explodes
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More Planetary Nebulas: the Orion Nebula (top) & Eagle Nebula (bottom)
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Poor little dying star• The light & heat of a supernova fade away
eventually.• The remnants become a nebula that can be
used to make more stars.• All that remains of the original star is a core
made entirely of neutrons, called a neutron star.
• This super-dense object is no more than a few-kilometers in diameter.
• A pulsar is simply a neutron star that is spinning.
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Inside the crab nebula is a pulsar star, a type of neutron star.
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Sometimes its not the end…• The life of a star is not always finished
with the white dwarf. • Sometimes the star continues to contract
and its gravity increases.• Imagine that the Earth contracted.• First to half its size and then a quarter. • Then even smaller. Imagine that the
entire mass of the Earth was able to fit in your house.
• The gravity would be enormous.
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Sometimes its not the end…
• That's what happens with some stars.
• They continue to contract and their gravity increases.
• They become black holes.
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Strange Happenings• Black holes are areas in
space where there is a huge amount of mass in a very small space.
• The gravity of this mass is so great that everything in the area is pulled toward the mass.
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Strange Happenings
• Even light cannot escape… which is why we call them black holes.
• No object can escape the gravitational pull of a black hole.
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So, how do we know they exist?• Have we ever seen a black hole? No. • Actually you can't see a black hole because no
light escapes the event. • Astronomers use other ways to look for black
holes. • Since they have large masses and gravities,
they affect the surrounding stars and systems. • They have found evidence of black holes in
the dark centers of galaxies and systems that emit large amounts of x-rays.
• BrainPOP: Black Holes
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Age & the H-R Diagram
• This diagram shows the life cycle of a star.
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Stars & the HR Diagram
QuickTime™ and a decompressor
are needed to see this picture.
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Summary
• BrainPOP: Life Cycle of Stars