Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass...
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Transcript of Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass...
![Page 1: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/1.jpg)
Stellar Evolution – the Life and Death of a
Star…Here’s the story we’ll tell…• Lowest mass stars and their evolution• Low mass star evolution• High mass star evolution• Stellar death, and stellar corpses• Origin of the chemical elements – stars do
it!
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Stars: always born in star clusters!
• Low temperature requires shielding from the radiation of other stars; requires dust which requires a lot of mass, since dust is a relatively rare component of interstellar clouds
• Star clusters forming in today’s environment are called “open star clusters”, dozens to hundreds of stars
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Size vs mass for planets, bd’s,stars
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Stellar Evolution: How stars live and die
• Visualize stellar evolution as a path on the H-R Diagram
• Remember, it’s a plot of Surface Temperature vs. Luminosity
• Where do you suppose stars first appear on the diagram? Ponder……
![Page 8: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/8.jpg)
HR pre main sequence sun
![Page 9: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/9.jpg)
Another Quick Overview First…
• Stars burn through their hydrogen, evolve off Main Sequence to become Red Giants, then die in various ways
• High mass stars evolve fast,… • Low mass stars evolve slowly
![Page 10: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/10.jpg)
HR main sequence turnoff
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The H-R Diagram of a Star Cluster
•All Stars born at the same time, only differ in their mass•Stars age at different rates, depending on their mass. More mass = faster evolution•Stellar Evolution web simulator
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HR of star clusters vs age
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M55 HR diagram
![Page 14: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/14.jpg)
Evolution of Low Mass Stars• Note! I distinguish between low and medium
mass stars – the book calls all of them “low mass”.
• Begin with H burning in core• When H runs out, core collapses under
gravity, releasing grav potential energy, raising star’s luminosity
• Core collapse stops when “electron degeneracy” sets in. Electrons are “elbow to elbow” (in a quantum mechanical sense)
![Page 15: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/15.jpg)
Layers; main seq vs. giant
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Medium Mass Star Evolution
• H burning until all H is He, then core collapse, releasing gravitational potential energy, raising luminosity and expanding the star ~ x100 times
• Core density and temperature rises until 100 million K. Then…..
• Well, you tell me – what are the options for further fusion? We have H and He floating around in the core…
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Be per nucleon
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Helium burning layer
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Sun to red giant cartoon
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HR tracks to red giant
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Sun and red giant side by side
![Page 22: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/22.jpg)
Sun’s L vs time
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We’re all doomed
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HR with instability and variables
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The End of the Line for Medium Mass Stars like the Sun…
• Added luminosity is so strong, it lifts the red giant’s low density outer envelope completely off the star.
• As it expands, its opacity drops and we see to a deeper and deeper and hotter and hotter depth, so the star moves left on the HR diagram
• Until… we see the electron degenerate core; the new white dwarf created at the center
• This core can now cool, as it can’t collapse further and it is exposed to the cold of outer space.
• Thus, it follows the cooling curve of a white dwarf; down and to the right on the HR diagram
• So, what we see is a hot stellar corpse surrounded by an expanding and thinning cloud of flourescent gas = a Planetary Nebula
![Page 26: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/26.jpg)
HR track to PN stage
![Page 27: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/27.jpg)
White dwarf->pN shell w velocity
![Page 28: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/28.jpg)
Green fuzzball
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PN misc young
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Cateye nebula
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Dumbell
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Dumbell hst upclose details
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Egg burst nebula
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Helix Nebula
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Ic 4406 P
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Little Ghost PN
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NGC 2346 pn
![Page 38: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/38.jpg)
Pn abell 39
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NGC 2440 pn
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NGC 6751 PN (blue eye)
![Page 41: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/41.jpg)
Ring Nebula
![Page 42: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/42.jpg)
PN flying badminton
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PN misc
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Spirograph PN
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Eskimo lowres
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Eskimo hi res
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Evolution of High Mass Stars – Short and Violent
Lives• Have enough mass to heat & compress core
to fuse all the way up to iron• Iron – the most stable, most tightly bound of
all nuclei• All fusion or fission involving iron will subtract
heat from the star’s core, not add to it. “Danger! Danger Will Robinson!”
![Page 48: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/48.jpg)
Layers of a pre SN II
![Page 49: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/49.jpg)
Eta Carinae
![Page 50: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/50.jpg)
Ant nebula
![Page 51: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/51.jpg)
Wolf-rayet star
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The Death of High Mass Stars…
• When iron core exceeds about 1.4 solar masses, the temperature becomes high enough to cause nuclear reactions for iron
• Nuclear burning causes further core collapse, which raises the density and accelerates the nuclear reactions.
• In 0.2 seconds (!) the core collapses, fusing iron into lighter and also heavier elements
• This is the ONLY place in the universe that elements heavier than iron are made!
• Neutrinos produced, so vast in number that they blow apart the star…
![Page 53: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/53.jpg)
Be per nucleon
• Be per nucleon
![Page 54: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/54.jpg)
Supernova! (SN II)• 99% of energy release, the gravitational
potential of the star, goes into neutrinos• 1% goes into the explosion• 0.01% goes into visible light. Still, the light
is bright enough to equal the entire galaxy of 100 thousand million stars (Gah!)
• SN II are the only place in nature where the elements heavier than iron are produced
![Page 55: Stellar Evolution – the Life and Death of a Star… Here’s the story we’ll tell… Lowest mass stars and their evolution Low mass star evolution High mass.](https://reader036.fdocuments.in/reader036/viewer/2022062905/5a4d1ad07f8b9ab059971443/html5/thumbnails/55.jpg)
Let’s look at some ancient supernova remnants…
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Cass A
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Cass A colored
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Cass A upclose
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Kepler’s snr
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LMC SNR
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Another LMC SNR
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SNR H-alpha
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Pencil nebula snr
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Veil Nebula (entire)
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Cygnus loop SNR
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Veil closeup1
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Crab HST
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Grav redshift
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Neutron star layers
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Egg nebula pulsar
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Crab center w jet
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Cerenkov radiation diagram
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Crab center w jet sequence
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Crab HST center upclos
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Let’s look at another Pulsar. This one is in the globular star
cluster 47 Tucanae…
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47 Tuc – ground based
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47 Tuc HST
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Millisecond pulsar
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How to Detect Neutrinos?
• Like, neutrinos from supernova explosions• …or neutrinos from the sun (the strongest source
because it’s so close)• - once in a great while a neutrino will hit an
electron and deposit its energy, accelerating the electron to almost the speed of light. This rapid acceleration causes the electron to give of photons of light = synchrotron radiation
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Sudbury neutrino detector
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The Cosmic Abundances of the Chemical Elements
• Due to the nuclear fusion in the cores of stars• And… to supernova explosions• Remember – Supernova explosions are the ONLY
place in the universe where heavy elements are created!
• All the elements beyond Iron in the periodic table (gold, silver, uranium, copper…) are created ONLY in the core collapse of a supernova explosion.
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Abundances of all elements
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Abundances of all elements graph
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Cosmic Rays…• The blast of a supernova explosion sends out
elementary particles at near the speed of light. These get further accelerated by magnetic fields in the galaxy.
• When they impact earth, they smash into our atmosphere and create cosmic ray air showers…
• Cosmic rays are a significant source of genetic mutations. Cancer odds are higher the higher the elevation you live, in part because of more cosmic ray exposure!
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Cosmic ray airshower
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What happens if the stars are in a close binary
system?
• This happens a lot! Nearly half the stars in our Galaxy are members of binary star systems
• Roche lobe defines gravitational “backyard” for each star
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Mass transfer binary (art)
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Mass transfer accretion disk
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X-ray binary art
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Nova sequence
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But with all this mass falling onto the white dwarf, there’s
another possibility…
• … something more ominous… more terrifying… more…. Scary!
• What could that BE?!
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Carbon Bomb Supernova (SN type I)
• If the white dwarf is close to the 1.4 solar mass upper limit that electron degeneracy can support…
• The added mass could push it past the limit before it gets hot enough to flash off
• Then, star collapses under the weight and because it is electron degenerate, energy created will not expand the star and shut off the fusion.
• So, entire star (carbon, mostly) undergoes fusion at once. What a star normally takes billions of years to burn, this star burns all at once. BIG explosion!
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SN Ia sequence
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Supernova! (SN I)• These are even brighter than SN II’s from
massive stars.• Very useful – they’re all the ~same – 1.4 solar
mass white dwarfs undergoing nuclear fusion. This turns out to mean they are…
• GREAT “standard candles” – objects of known luminosity, on which we can then use simple math to determine their distance.
• So, any SN I and its host galaxy, we can find it’s distance, even out to the edge of the observable universe, since they are so bright.
• Huge amount of observational effort today is going into discovering and charting the light curve of SN I’s throughout the universe!
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SN Ia light curves
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3 Possible Ends of a Stellar Corpse!
• If mass < 1.4 Msun = White Dwarf
• If 1.4Msun < M < 3 Msun = Neutron star
• If M > 3 Msun = Black Hole!
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Tole cartoon