The Life Cycle of a Star A Really “Hot” Topic By Samantha Edgington.
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Transcript of The Life Cycle of a Star A Really “Hot” Topic By Samantha Edgington.
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The Life Cycle of a Star
A Really “Hot” Topic
By Samantha Edgington
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Objectives
• Describe how stars are formed.
• Explain the concept of equilibrium.
• Define the “death” of a star.
• Identify the different types of stars.
• Describe how the process of nuclear fusion works within a star.
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What is a Nebula?• A nebula can be defined as a
thinly spread cloud of interstellar gas and dust.
• Some nebulae are the remains of a supernova explosion.– the death and collapse of a massive
star can cause this explosion, this means nebulae can be the remains of old, dead stars.
• Most nebulae are gravity-induced condensations of gases where protostars are born.
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How is a Protostar Formed?
• Inside a nebula, there are areas where gravity causes dust and gas to “clump” together.
• As these “clumps” gather more and more mass their gravitational pull increases, forcing more atoms together.
• This process is known as accretion, and the result is a protostar.
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How does a Protostar Become a Star?
• In order to comprehend this process, the concept of equilibrium must be understood.
• Equilibrium is in essence a balance.
• In the case of star formation this balance exists between gravity and gas pressure.
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Achieving Equilibrium
• First gravity pulls gas and dust inward towards the core of the prospective star.
• Inside the core, density and temperature increases as atomic collisions increase, causing a rise in gas pressure.
• Finally when gas pressure is equal to gravity, the protostar has reached equilibrium and is therefore reached a reasonably stable size.
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The Birth• Once the protostar has
achieved equilibrium one of two things occur:
If there is not a sufficient mass, it becomes a brown dwarf which is a “star” that doesn’t radiate much heat and light.
In the event it does contain an appropriate amount of matter, nuclear fusion begins and light is emitted.
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The Main Sequence• A star is basically a huge ball of gas undergoing
nuclear fusion.• The main sequence phase is where stars spend
the majority of their “life” by fusing hydrogen into helium.
• There are two types of main sequence stars:a red giant which is a large bright
star with a cool surface.a red dwarf which are very cool, faint
and small stars
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The Ending of Main Sequence• The star slowly shrinks over billions
of years as the hydrogen is used by fusion.
• The star’s temperature, density, and pressure at the core continues to increase.
• Once the hydrogen is depleted, the helium is fused into carbon, when this occurs the star has reached “old age”.
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The Death• There are one of two ways a star can die
depending on its size.
• If the star is of low mass, it expands its outer layers, creating nebulae and a white dwarf forms from the core.
• If it is of high mass, death occurs in a massive explosion known as a supernova, the remaining core then transforms into a neutron star or a black hole.
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What is a White Dwarf?
• They form from the core of a dead red giants that were too small to fuse carbon.
• Since they do not undergo fusion, they have no energy source and gradually fade.
• When they radiate away all of their energy they will theoretically become a black dwarf.
• Since white dwarfs cannot be older than the universe (13.7 billion years) no black dwarfs are currently in existence.
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What is a Supernova?
• They can form when the gravitational potential energy—created by a sudden gravitational collapse of a large red giant—heats and expels the star's outer layers, resulting in an explosion.
• Also, they can form when a white dwarf ignites carbon fusion, which results in a runaway nuclear fusion reaction and causes a supernova.
• Supernovae can be so immense that the energy produced can equal the energy the Sun creates over a time period of 10 billion years!
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What is a Neutron Star?
• A neutron star is formed as a result of a massive star being compressed.
• The core material, known as neutron degenerate matter, mostly consists of neutrons with a few protons and electrons.
• The gravity is so intense that if an object were to reach the surface it would disperse all of its subatomic particles and merge with the star!
• The matter is so dense that a teaspoon would weigh billions of tonnes!
• Some people view neutron stars as giant atoms.
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What is a Stellar Black Hole?
• If a collapsing star exceeds the maximum mass a neutron star can be it will develop into a stellar black hole.
• Black holes are extremely dense areas with a gravitational pull so powerful not even light can escape!
• What could be a reason why black holes are black?
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Chart of the Stars
Star Type Solar Mass Temperature (K) Color
Red Giant 10 - 15 2,500 - 3,500 orange - red
Red Dwarf 0.1 - 0.5 2,500 – 3,500 red
Blue Giant 10 - 15 ~30,000 blue - white
Brown Dwarf 0.013 - 0.084
~1,000 red
Yellow Dwarf 0.8 -1 5,300 - 6,000 white - yellow
White Dwarf < 1.4 4,000 - 150,000 white
Neutron Star 1.4 - 3 ~1,000,000 blue
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The Sun’s Life
• Now that a basic overview of a star’s life cycle has been covered, the details of the most important star’s life can be revealed.
• Can you guess what type of star the Sun is?
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The Sun in Main Sequence
• The Sun was born like any other star, out of a nebulae and into a protostar.
• It is now in its main sequence and can be classified as a yellow dwarf.
• The Star is about 4.57 billion years old, about halfway through its complete lifecycle.
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The Sun’s Death• Since the Sun is considerably smaller it will
not explode in a supernova.• Instead it is predicted that it will become a
red giant in about ~6 billion years.• When this occurs, all the water on earth will
be vaporized and life will cease to exist.• In the final phase the Sun will form a white
dwarf and slowly fade out of existence.
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Works Cited• www.dictionary.com
• aspire.cosmicray.org/labs/star_life/starlife_proto.html
• www.astro.keele.ac.uk/workx/starlife/StarpageS_26M.html
• http://www.telescope.org/pparc/res8.html
• www.antonine-education.co.uk
• www.darkstar1.co.uk
• www.pbs.org
• outreach.jach.hawaii.edu
• www.spaceflightnow.com
• wikipedia.org• www.cosmographica.com