the life & death of stars. nuclear fusion nebula supernova black hole
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Let’s review: What is a star? Giant ball of hot gases The huge objects in the universe Our Sun is an example of a star Made of mainly hydrogen and some heliumTRANSCRIPT
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The Life & Death of Stars
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Nuclear fusion
Nebula
Supernova
Black hole
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Let’s review: What is a star?
• Giant ball of hot gases• The huge objects in
the universe• Our Sun is an example
of a star• Made of mainly
hydrogen and some helium
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How do stars generate energy?
• Stars burn by a process called nuclear fusion• This process combines two hydrogen atoms
into one helium atom, which then fuse to form elements with even more protons
• This process gives off a lot of heat & energy• Gives the illusion of “burning”
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Types of stars• 3 main sizes of stars
• Small/medium (like our Sun)• Large (aka giant)• Very large (aka supergiant or hypergiant)
• Different colours of stars indicate they’re different temperatures• Blue is hottest• Yellow is average• Red is ‘coolest’
• Usually, the bigger the star, the cooler it is• Most big stars are called Red Giants because they’re relatively cool• Blue giants are very rare
• The hotter the star, the shorter its lifespan
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Sizes of stars1) small / med – most common2) large – rare3) extremely large – very rare
• The Sun is a med (average) sized star
• Small stars are called dwarf stars
• Large stars are called Giants
• Extremely large stars are called Supergiants
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The Birth of a Star• All stars start out the same way, as
a nebula• A nebula is a giant cloud of gas
and dust• Stars are created in a nebula as the
gases contract due to the force of gravity, turning into a hot, dense clump
• As they become larger, they heat up until they reach a temperature of 10 000 000 C
• At this temperature, nuclear fusion begins
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A Star’s Life • For the major part of a star’s life, it
undergoes nuclear fusion• Lower-mass stars can undergo this
process for up to 100 BILLION years!
• Stars like the Sun can last for about 10 billion years
• Higher-mass stars produce energy for only a few million years
• Fast-burning, hot (blue) stars only last for a million years… yikes!
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A Star’s Death • A Star begins to “die” when the
hydrogen that fuels it runs out • H has fused into new substances (He)
• Outer layers swell• Once the core fuses into lead, fusion
stops and the star collapses inward, followed by an outward projection of particles
• Depending of the star’s size, its collapse is either in the form of a planetary nebula or a supernova
• After that, it then becomes one of the following:1) White dwarf (small/medium-sized stars)2) Neutron star (large stars)3) Black hole (extremely large stars)
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Supernovas• In 1987, Canadian astronomer
Ian Shelton discovered one while working at an observatory in Chile
• His discovery was by accident!• He was looking at images of
stars when he noticed something unusual: one star looked MUCH brighter than the others
• Named it SN 1987A and it is 163 000 light years away• This means Shelton was looking at the
supernova the way it was 163 000 yrs ago!
• SN 1987A was the closest one to Earth since 1604
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White DwarfsLife After Death of Small & Medium
Stars• When the star’s core
becomes lead it can not undergo fusion any longer
• This white hot ball of lead is called a white dwarf
• It cools over a loooong time to form a black dwarf star
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Neutron Stars Life after death of a large star
• Sometimes a star is so heavy & under so much pressure that it cannot support its weight (even if it’s fused into lead!)
• The atoms collapse even further creating a ball of neutrons
• This forms a rapidly spinning neutron star that is only a few kilometers in size
• We see neutron stars from the radiation that shoots out of either end
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Black holesThe Life After Death of Huge Stars
• Sometimes a star is so heavy that not even the neutrons can stay apart
• The neutrons crash together, forming a black hole
• After that we are not sure as this creates a black hole
• A black hole is an object so dense that not even light can escape it
• We can find black holes by looking for objects in space that are orbiting seemingly empty space
• These are very, very rare
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How will our Sun die?
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Death of a Biiiig Star
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Life Sequence of StarsStar’s Size Phases of a star’s “life & death”
Small/Mediumnebula nuclear fusion red giant planetary nebula white dwarf black dwarf
Largenebula nuclear fusion red supergiant supernova neutron star
Extremely Largenebula nuclear fusion red supergiant supernova black hole
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Life cycle of Stars… in pictures
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