Chapter 25 Chapter 25 Stars and Galaxies Stars and Galaxies Section 2 Section 2 Stellar Evolution Stellar Evolution Notes 25-2 Notes 25-2
Jan 04, 2016
Chapter 25Chapter 25Stars and GalaxiesStars and Galaxies
Section 2Section 2
Stellar EvolutionStellar Evolution
Notes 25-2Notes 25-2
NebulaNebula
First stage of a starFirst stage of a star’’s lifes life Cloud of dust and gasCloud of dust and gas
70% H, 28% He, 2% heavy elements70% H, 28% He, 2% heavy elements Begins to contract when a star near by Begins to contract when a star near by
explodes or another nebula collides with itexplodes or another nebula collides with it Gravity increases as the matter gets closerGravity increases as the matter gets closer
Region of dense matter shrinks and begins to Region of dense matter shrinks and begins to spinspin
Rate of spin increases as shrinking continuesRate of spin increases as shrinking continues
NebulasNebulas
ProtostarProtostar
Shrinking, spinning gases flatten into a Shrinking, spinning gases flatten into a disk with a central portion called a disk with a central portion called a protostarprotostar
Pressure builds and temperature buildsPressure builds and temperature buildsEventually the gas heats to the point it Eventually the gas heats to the point it
becomes plasma (millions of years)becomes plasma (millions of years)Temp. increases to 10,000,000Temp. increases to 10,000,000°C°CNuclear fusion beginsNuclear fusion beginsA star is bornA star is born
ProtostarProtostar
Main Sequence StarsMain Sequence Stars
Second stage of life for a starSecond stage of life for a starLongest stage of lifeLongest stage of life
Fusion releases energy as hydrogen Fusion releases energy as hydrogen atoms fuse to become helium atomsatoms fuse to become helium atoms
Energy moves outward but is kept in Energy moves outward but is kept in check by gravitycheck by gravity
Star maintains a stable size while there is Star maintains a stable size while there is enough hydrogen to keep fusion goingenough hydrogen to keep fusion going
Sun (Main Sequence Star)Sun (Main Sequence Star)
Giants and SupergiantsGiants and Supergiants
Third stage in the life of a starThird stage in the life of a starWhen almost all of the hydrogen has fused When almost all of the hydrogen has fused
into heliuminto heliumCore of star contracts and causes increased Core of star contracts and causes increased
temperaturestemperaturesThis allows for the fusion of helium atoms into This allows for the fusion of helium atoms into
carbon atomscarbon atoms
He and H fusion cause lots of energy that He and H fusion cause lots of energy that causes the outer shell to expandcauses the outer shell to expand
Giants and SupergiantsGiants and Supergiants
As it expands it becomes coolerAs it expands it becomes cooler It is no longer a main sequence starIt is no longer a main sequence star
It is now a red giant or red supergiantIt is now a red giant or red supergiantGiants 10 times bigger than the sunGiants 10 times bigger than the sunSupergiants 100 times bigger than the sunSupergiants 100 times bigger than the sun
Scientist estimate that the sun has only Scientist estimate that the sun has only converted 5% of its original hydrogenconverted 5% of its original hydrogenStill lots of time until the giant stageStill lots of time until the giant stage
SupergiantSupergiant
White DwarfWhite Dwarf
Last stages of a giant starLast stages of a giant starStar loses its outer gasesStar loses its outer gases
Core showsCore showsA planetary nebula occurs when the outer A planetary nebula occurs when the outer
gases are heated by the core and escapegases are heated by the core and escapeThe core collapses and leaves a hot, The core collapses and leaves a hot,
dense mass – white dwarfdense mass – white dwarf
White Dwarf in Planetary NebulaWhite Dwarf in Planetary Nebula
White Dwarf
Black DwarfBlack Dwarf
A white dwarf can cool and become faintA white dwarf can cool and become faintOnce it no long gives off energy it is deadOnce it no long gives off energy it is dead
Called a black dwarfCalled a black dwarfDonDon’’t exist yett exist yetThe universe isnThe universe isn’’t old enough to have t old enough to have
produced any yetproduced any yet
NovaNovaA white dwarf can have a different endingA white dwarf can have a different ending It can explodeIt can explode
Called a Nova Called a Nova May become a nova more than onceMay become a nova more than once
Becomes 1 million times brighter than the Becomes 1 million times brighter than the sunsunBrightness lasts only a few days then it Brightness lasts only a few days then it
returns to normalreturns to normalBelieved only to happen when a white Believed only to happen when a white
dwarf revolves around a main sequence or dwarf revolves around a main sequence or giant stargiant star
SupernovaSupernova
Last stage of a supergiantLast stage of a supergiantSupergiant explodes up to 100 times Supergiant explodes up to 100 times
brighter than a novabrighter than a novaBlows itself apartBlows itself apart
Fusion begins againFusion begins againCarbon fuses into heavier elements like Carbon fuses into heavier elements like
magnesiummagnesiumThese fuse into ironThese fuse into iron
SupernovaSupernova
Fusion continues until the core is ironFusion continues until the core is iron Iron absorbs energy from the gravity Iron absorbs energy from the gravity
contracting the mattercontracting the matterCore collapses and causes the outer layers to Core collapses and causes the outer layers to
explodeexplode
Neutron StarNeutron Star
The core of a supernova contracts to form The core of a supernova contracts to form a neutron stara neutron starMost dense star in the universeMost dense star in the universe
One spoonful of the star would weigh 100 million One spoonful of the star would weigh 100 million tons on the earthtons on the earth
Neutron star rotates quicklyNeutron star rotates quicklyCan give off two beams of radiation Can give off two beams of radiation
Called pulsarsCalled pulsars
Black HoleBlack Hole If the core of the supernova is too If the core of the supernova is too
massive, it wonmassive, it won’’t make a neutron star but t make a neutron star but instead a black holeinstead a black hole
It is so massive and gravity so strong that It is so massive and gravity so strong that not even light can escape itnot even light can escape it
Can only detect black holes by observing Can only detect black holes by observing the matter and stars around itthe matter and stars around itXrays are given off just before matter is pulled Xrays are given off just before matter is pulled
into the black holeinto the black holeCan see the XraysCan see the Xrays
More SitesMore Sites
http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html
http://amazing-space.stsci.edu/resources/explorations/blackholes/
Very cool site!Very cool site!
http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html