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Stellar Stellar EvolutionEvolution
Or How and Where do Or How and Where do stars come from?stars come from?
Let’s follow the evolution Let’s follow the evolution of a star the same size as of a star the same size as the sunthe sun
End product G class starEnd product G class star
1 solar mass – 2 x 101 solar mass – 2 x 103030 kg kg
Surface temp. ~ 6000 KSurface temp. ~ 6000 K
Where did the gas clouds Where did the gas clouds come from?come from?
The big bangThe big bang
Supernova explosionsSupernova explosions
Where did the sun come Where did the sun come from?from?
The sun is a third generation starThe sun is a third generation star It formed from a supernova It formed from a supernova
explosion that happened about 5 explosion that happened about 5 billion years agobillion years ago
How does a nebula form a How does a nebula form a star?star?
A nebula, or interstellar cloud, is A nebula, or interstellar cloud, is the beginning stage of a star the beginning stage of a star (Stage 1)(Stage 1)
Witch’s Head NebulaWitch’s Head Nebula
These are stars in the middle of the Rosetta Nebula
Stage 2Stage 2
Gas cloud starts to contract due to Gas cloud starts to contract due to gravitygravity
Stage 3Stage 3•Gas starts to heat upGas starts to heat up•Near the end of stage 3, the star is Near the end of stage 3, the star is called a “Protostar”called a “Protostar”
Stage 4Stage 4
Begins around 100,000 years after Begins around 100,000 years after the cloud started contractingthe cloud started contracting
The protostar’s density and The protostar’s density and temperature increase temperature increase
Stage 5Stage 5•The “star” is heading toward the The “star” is heading toward the main sequencemain sequence•These are often called T Tauri starsThese are often called T Tauri stars
This is a protostar This is a protostar blowing away blowing away excess gas and excess gas and dustdust
This is a T Tauri This is a T Tauri star formingstar forming
Stage 6Stage 6
At 10 million years the protostar has At 10 million years the protostar has shrunk shrunk
-the core density and pressure are high -the core density and pressure are high enough for nuclear enough for nuclear fusionfusion to start to start
It is now called a “Star”It is now called a “Star” For 30 million more years the star For 30 million more years the star
contracts a little more and settles down contracts a little more and settles down to the main sequenceto the main sequence
And then finally, after a total of 40-50 And then finally, after a total of 40-50 million years…million years…
Stage 7, main sequence. The star Stage 7, main sequence. The star has “arrivedhas “arrived”
What about other size What about other size stars?stars?
Larger massLarger mass (>1 solar (>1 solar mass)mass)
Get to main sequence Get to main sequence quickerquicker
Burn much brighter Burn much brighter and fasterand faster
Largest can become a Largest can become a star in <1 million star in <1 million yearsyears
Smaller massSmaller mass (<1 solar (<1 solar mass)mass)
Take longer to get to Take longer to get to main sequencemain sequence
Burn dimmer and Burn dimmer and longerlonger
<.08 solar masses <.08 solar masses never become stars, never become stars, these are called these are called “Brown Dwarfs”“Brown Dwarfs”
Once again let’s follow the Once again let’s follow the Sun’s evolutionSun’s evolution
Right now about halfway through Right now about halfway through its 10 billion year lifespanits 10 billion year lifespan
Burning Hydrogen in its coreBurning Hydrogen in its core
Middle aged looking forward Middle aged looking forward toward retirementtoward retirement
From Hydrogen to HeliumFrom Hydrogen to Helium
Inside core Hydrogen keeps burningInside core Hydrogen keeps burning A Helium “ash” forms in the very centerA Helium “ash” forms in the very center As the helium core grows a hydrogen As the helium core grows a hydrogen
burning shell surrounds itburning shell surrounds it The core density increases as it shrinks The core density increases as it shrinks
under gravity’s pressureunder gravity’s pressure Core temp. increases causing H burning Core temp. increases causing H burning
to increaseto increase This causes the star to expand against This causes the star to expand against
gravity trying to pull it ingravity trying to pull it in
Stage 8Stage 8
As the star burns more Hydrogen, As the star burns more Hydrogen, it starts to swell. This is Stage 8-it starts to swell. This is Stage 8-the Subgiant phasethe Subgiant phase
The star continues to become a The star continues to become a Red GiantRed Giant
Stage 9Stage 9
If it were simple, the star would If it were simple, the star would continue to expand and cool offcontinue to expand and cool off
It’s not that simple, the core is in a It’s not that simple, the core is in a “degenerate” state“degenerate” state
When helium burning starts, the core When helium burning starts, the core heats with no change in pressure or size heats with no change in pressure or size in the corein the core
This increase in temp causes a “Helium This increase in temp causes a “Helium Flash,” the star burns uncontrollably for Flash,” the star burns uncontrollably for a few hoursa few hours
This is a red giant star This is a red giant star with a dust ring around itwith a dust ring around it
Stage 10Stage 10
The core now is steadily burning The core now is steadily burning heliumhelium
The star resides in a stable area off The star resides in a stable area off the main sequence called the the main sequence called the “Horizontal branch”“Horizontal branch”
It remains here for 50-100 million It remains here for 50-100 million yearsyears
Stage 11Stage 11
As the temperature in the core As the temperature in the core increases, helium starts to burn and increases, helium starts to burn and form carbonform carbon
The core now becomes carbon ashThe core now becomes carbon ash This core is surrounded by a helium This core is surrounded by a helium
burning shell and around that a burning shell and around that a hydrogen burning shellhydrogen burning shell
Like before, the star swells, this time Like before, the star swells, this time becoming a Red Supergiantbecoming a Red Supergiant
Which Red Supergiant is Which Red Supergiant is this?this?
Betelgeuse Betelgeuse Betelgeuse
This is what will happen to This is what will happen to the sunthe sun
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Where do we go from Where do we go from here?here?
The core is now building up carbon The core is now building up carbon ashash
Temp. is approaching 300 million KTemp. is approaching 300 million K This isn’t hot enough for the next This isn’t hot enough for the next
step in fusionstep in fusion The core becomes more dense and The core becomes more dense and
the outer shell expands. This is the outer shell expands. This is stage 12. It continues until the final stage 12. It continues until the final part of this stage.…part of this stage.…
The outer shell is thrown The outer shell is thrown off as a planetary nebulaoff as a planetary nebula
The star that is left is a white dwarf, this is The star that is left is a white dwarf, this is Stage 13Stage 13
This will eventually cool to become a black This will eventually cool to become a black dwarf, this is the final stage, Stage 14dwarf, this is the final stage, Stage 14
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Here is an example from Here is an example from start to finishstart to finish
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That’s all folksThat’s all folks
You might have a questionYou might have a question
What is a white dwarf?What is a white dwarf? What happens to smaller mass What happens to smaller mass
stars?stars? What happens to larger mass What happens to larger mass
stars?stars?
White DwarfsWhite Dwarfs
The carbon core made during The carbon core made during helium burning is all that is lefthelium burning is all that is left
It is extremely dense and hotIt is extremely dense and hot The only thing stopping it from The only thing stopping it from
collapsing is electron pressurecollapsing is electron pressure It is only the size of the earthIt is only the size of the earth One teaspoon would weigh about One teaspoon would weigh about
20 million tons20 million tons
These are cooling White These are cooling White DwarfsDwarfs
Black DwarfBlack Dwarf
The white dwarf is extremely The white dwarf is extremely brightbright
Since there is no longer fusion, it Since there is no longer fusion, it will eventually coolwill eventually cool
It will become a black dwarfIt will become a black dwarf
Smaller mass StarsSmaller mass Stars
Smaller mass stars follow almost Smaller mass stars follow almost exactly the same sequence as the exactly the same sequence as the sunsun
It takes them longer to burn all It takes them longer to burn all their fuel, so they exist in the their fuel, so they exist in the different stages for longer timesdifferent stages for longer times
Sometimes something Sometimes something cool happenscool happens
A white dwarf can output a huge A white dwarf can output a huge amount of light amount of light
This is called a NOVAThis is called a NOVA
How does this happen if a white How does this happen if a white dwarf is no longer generating dwarf is no longer generating energy?energy?
It happens when the white It happens when the white dwarf is not alonedwarf is not alone
It has a companion starIt has a companion star Matter is taken from the companion and Matter is taken from the companion and
builds up on the white dwarf, this is mostly builds up on the white dwarf, this is mostly Hydrogen and HeliumHydrogen and Helium
When enough builds up, fusion starts in this When enough builds up, fusion starts in this shell and it violently burns and explodes shell and it violently burns and explodes
This causes the white dwarf to flare into a This causes the white dwarf to flare into a Nova Nova
Nova means “new” and to early observers Nova means “new” and to early observers these stars appeared newthese stars appeared new
This is what is happening This is what is happening in a Novain a Nova
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A Nova in AquillaA Nova in Aquilla
This is the shell blown off This is the shell blown off from a Nova in Cygnus from a Nova in Cygnus that happened in 1992that happened in 1992
This nebula only became This nebula only became visible after the Nova in visible after the Nova in CygnusCygnus
This tiny Ball is theGas fromThe Nova
What about those larger What about those larger mass Stars?mass Stars?
They can become neutron starsThey can become neutron stars
Or if even more massive, “Black Or if even more massive, “Black Holes”Holes”
But, that’s a story for another timeBut, that’s a story for another time
SourcesSources www.cdnow.com www.wavcentral.com www.tidalwaves.com www.nonstick.com SmashmouthSmashmouth JourneyJourney Hubble Space Telescope CenterHubble Space Telescope Center Astronomy A Beginners guide to theAstronomy A Beginners guide to the UniverseUniverse, ,
Chaisson and McMillanChaisson and McMillan Paul for his helpPaul for his help Julie for her Sting musicJulie for her Sting music