Term
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Definition
| Birthplace of Stars: Mass from 10^2 to 10^6 solar masses with a size up to 10pc and a temperature from 10-50K. Star forming region with a lot of H, C, and O/ |
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Term
| Basic Picture of Star Formation |
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Definition
1. Dense parts of interstellar clouds can collapse under their own gravity
2. As the collapse progresses, the center of the cloud becomes denser and hotter
3. The pressure in the core soon builds up enough to stop the rapid collapse. This takes just 10^4 to 10^6 years.
4. The core, now called a protostar, continues to shrink slowly, becoming hotter as it does.
5. The center of the protostar becomes so hot that hydrogen begins to fuse to helium. It has become a star! |
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Term
| A more realistic picture of star formation: Collapse from a Rotating Interstellar Cloud |
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Definition
1. A dense cloud of cold interstellar gas rotating slowly
2. Free-fall collapse. Speed of rotation increases.
3. 10^5 years core becomes hot, free-fall collapse ends, protostar forms
4. Slow contraction, protoplanetary disk forms, mass loss in polar winds and jets |
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Term
| The formation of stars the final approach to the main-sequence |
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Definition
1. 10^7 years hydrogen fusion begins. Star stops contracting and reaches the main sequences
2. 10^8 years Last of the gas and dust blown away, leaving the star and possibly a planetary system |
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Term
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Definition
| The nebula where the star formed is blown away by wind and radiation from the stars, revealing the new-born star cluster |
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Term
| Star's life continuous struggle for survival. |
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Definition
Gravity tries to force stars to shrink
to a size as small as possible – turning into black holes is its ultimate goal – but it doesn’t always gets it way! Stars resist the force of gravity for a while –– 10^7 – 10^10 years depending on their mass –– but eventually they succumb to the fatal attraction, and collapse to a white-dwarf, or to a neutron star or a blackhole. |
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Term
| How do stars resist gravity's fatal attraction? |
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Definition
| I think electro-magnetism or gas pressure |
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Term
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Definition
| The higher the temperature, the faster the particles move and larger the pressure. To maintain high temperature stars rely on nuclear burning |
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Term
| Energy produced by fusing hydrogen to helium |
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Definition
| about .71% of the hydrogen mass is converted to energy |
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Term
| Models for the interior of the sun |
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Definition
| Energy Energy is transported by radiation in the inner layers of the sun, by convection in the outer layers. The boundary between the two regions is at 0.71 solar radius. |
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Term
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Definition
| The Balance of Pressure against Gravity. Pressure and gravity must balance or the star will expand or contract.Upward pressure of force, downward force of gravity |
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Term
| The Energy Generation Rate Inside the Sun |
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Definition
| All the nuclear energy in the sun is produced inside .2 solar radius |
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Term
| The Abundance of Hydrogen and Helium in the Sun |
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Definition
| The models show that the sun has used 1/2 of the original hydrogen in its core. |
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Term
| The Temperature Inside the Sun |
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Definition
| The temperature at the center of the sun is a bit more than 15 million K |
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Term
| The Density Inside the Sun |
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Definition
| At the center the density is 10 times that of lead but at the surface it is 10000 times less than that of the Earth's atmosphere |
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Term
| Super-Kamiokande Solar Neutrino Telescope |
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Definition
Super-K is located 1,000 m (3,281 ft) underground in Kamioka Mining and
Smelting Co. It consists of a cylindrical stainless steel tank that is 41.4 m (135.8 ft) tall and 39.3 m in diameter holding 50,000 tons of ultra-pure water. Looks for neutrinos |
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Term
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Definition
Physics tells us there are actually 3 kinds of neutrinos: ordinary electron-neutrinos and two other kinds of neutrinos.
• We now know that the ordinary neutrinos from the sun turn into the other types of neutrinos while traveling to the Earth,leaving 1/3 as many ordinary neutrinos.
• Early neutrino telescopes detected only ordinary neutrinos, missing the two exotic kinds. |
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Term
| Sudbury Neutrino Observatory |
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Definition
| The Sudbury neutrino telescope detects all three kinds of neutrinos and can distinguish one kind from another. |
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Term
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Definition
• The sun has used up half the hydrogen in its core in 4.7 billion years.
• It will use up rest of its hydrogen in the next 4.7 billion years.
• When it uses up its hydrogen, it has no more source of energy in its core, so its structure must change. It will leave the main sequence…
the sun will not explode, it will turn into a red giant and will heat the Earth to temperatures greater than that at the surface of Mercury, killing all life. |
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Term
| Why do stars change/evolve? |
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Definition
• Stars evolve because they run out of nuclear fuel of one kind and switch to another fuel (if they can), i.e. nuclear reactions change their chemical composition.
• When a main-‐sequence star has converted all its hydrogen into helium, it has run out of the “fuel” (temporarily) that was the source of its energy & support against gravity & it must change.
• Since all stars have nearly the same initial chemical composition, the way in which a single star evolves depends almost entirely on its mass.
• Binary stars evolve differently. |
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Term
| Relative radii of Stars in the H/R diagram |
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Definition
| So, if two stars have the same temperatures but different luminosities, their surface area ratio (or the ratio of radius squared) must be equal to the ratio of their luminosities. |
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Term
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Definition
| larger the star, the shorter the life-cycle. also if two stars have the same temperature, but one is larger, the larger one will be brighter |
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Term
| Main-Sequence Stars Evolve into Red Giants |
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Definition
When the main sequence star exhausts hydrogen in its core:
The core shrinks (gravity pulls it in when energy generation ends) becoming hotter and denser
The core becomes so hot and dense that hydrogen begins to fuse into helium in a thin shell around the core.
So much energy is produced in the shell that the outer layers of the star expand, turning the star into a red giant. |
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Term
| The Internal Structure of Red Giant Stars |
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Definition
| Luminosity up to 100 solar. Temperature is 3000K and radius is 50 solar. Core of He Radius is .01 solar. |
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Term
| Evolution beyond the Red Giant Branch |
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Definition
Evolution beyond the red giant branch is different for low and high mass stars.
1. Mass less than .7 solar: the star uses all the hydrogen in its envelope. The star becomes a white dwarf.
2. Mass greater .7 solar: The temperature and density in the core become high enough to fuse helium into carbon. The star becomes a horizontal branch star. |
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Term
| Transition from Red Giant Branch to Horizontal Branch |
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Definition
Helium begins to fuse to carbon in the "triple-alpha reaction"
He fusion spread rapidly throughout the core, so rapidly that it is called the "Helium Flash."
The Helium flash is not visible outside the star, though.
With the new source of energy, the pressure in the core increases and the core expands.
The overall size of the star shrinks a lot.
The luminosity of the star decreases somewhat. |
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Term
| The Transition from Horizontal Branch to AGB Star |
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Definition
The helium in the very center of the Horizontal Branch star runs out (it
is all converted to carbon and oxygen). The core no longer has a source of energy, and hence can’t resist the force of gravity.
• The core shrinks, becoming hotter and
denser. It has two parts: An inner core of carbon and oxygen surrounded by a thick layer of helium.
• Nuclear fusion begins in two thin layers at the boundaries of the two parts of the core.
• The amount of energy produced in the two thin layers is large. The luminosity and radius of the star increase greatly. |
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Term
| The Evolution of Stars with Masses between .07 Solar Masses and 8 Solar Masses |
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Definition
| Main Sequence %70. Red Giant 10%. Horizontal branch 20%. |
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Term
| Star Death --> White Dwarfs |
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Definition
• All nuclear reactions cease in the star after the planetary nebula is ejected.
• Without an energy source the remnant is a dead star, a white dwarf. It is luminous only because it used to be hot and takes a long time (billions of years) to cool off.
• The mass of the star is typically 0.6 solar masses and its radius is 0.01 solar masses.
• As it cools, it fades to oblivion, a dead cinder. |
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Term
| How are stars supported against gravity |
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Definition
Normal Stars (generate energy: are supported by ordinary gas pressure.
White Dwarf Stars (no energy generation): Electron degeneracy pressure
Neutron Stars (no energy generation): Neutron degeneracy pressure) |
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Term
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Definition
Pressure decreases with decreased temperature and the pressure goes to 0 as T--> 0
Particle velocity increases with increasing T and the pressure is due to particle velocity-- velocity & pressure --> 0 as T-->0 |
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Term
| Electron/neutron degeneracy pressure origin and facts |
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Definition
Quantum Physics (origin)
Gravity at the surface of white dwarf stars: million times stronger than Earth
Gravity at the surface of neutron stars: trillion times stronger than Earth |
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Term
| Quantum Uncertainty Principle |
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Definition
| Can't simultaneously measure the position and momentum of any particle exactly |
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Term
| Pauli's Exclusion Principle |
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Definition
| No two identical particles (electrons or neutrons) can occupy the same exact state, eg. free electrons must have different momenta. |
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Term
| Electron Degeneracy Pressure |
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Definition
| Electrons are NOT bound to nuclei but should be thought of as spread over a "cloud." |
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Term
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Definition
momentum (or velocity) is related to the frequency: higher momentum corresponds to higher frequency.
Two electrons can't have the same frequency. |
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Term
| White Dwarf Star Electron Facts |
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Definition
If you put 10^31 electrons in a cubic box of length 1 cm the x-component of their velocity will range from 1 cm/s all the way to the speed of light (3x10^10 cm/s)!
The mean density of a white-dwarf star of 1 solar mass is about 10^6 gram/cm3 and it has about 10^30 electrons per cm3; density = Mass/Volume.
These rapidly moving electrons provide a tremendous pressure and that prevents the white dwarf star – which has no energy source – from collapsing under the force of gravity. |
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Term
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Definition
| Don't collapse to a blackhole due to quantum laws governing the behavior of electrons; however, this works only up to a point. If a white dwarf star has mass larger than 1.4 solar masses- called the Chandrashekhar mass- than even electron degeneracy pressure can't prevent the star from collapsing to a blackhole (or explode) |
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Term
| Evolution of a massive star (look at diagram on slide show) |
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Definition
| Inter-Stellar Gas and Dust->Main Sequence-> Supergiant->Supernova-> either a neutron star (8-15) or black hole (15-100 solar masses) |
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Term
| Synthesis of elements in massive stars |
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Definition
| The core has layers of nearly pure elements separated by thin shells where lower-mass elements are fusing to higher-mass elements |
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Term
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Definition
Cased by the collapse of the iron core in highly evolved, high-mass stars:
• The iron core collapses when its mass becomes greater than 1.4 M.
• As the core collapses, its electrons are compressed and merge with
protons to form neutrons.
• The collapse continues until the neutrons become degenerate – the
entire collapse takes about 1 second.
• The core overshoots and bounces back.
• The bouncing core collides with overlying material in the outer core,
sending the material outward.
• Neutrino pressure (!) in the dense material helps eject the outer
layers. |
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Term
| The origin of the heavy elements and the chemical evolution of the galaxy |
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Definition
1. In the first generation of stars the abundance of heavy elements is low or zero
2. Some stars become supernovae, making heavy elements and ejected them
3. The ejected material enriches the interstellar gas and dust with heavy elements
4. New stars form with a higher abundance of heavy elements (back to #2) |
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Term
| Neutron Stars: end product of Supernovae |
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Definition
| A typical neutron star has a mass of 1.4 SM and a radius of 12 km (Austin). The star is so dense basically made up of solid neutrons (all buildings of Dallas compressed into a centimeter cubed). |
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Term
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Definition
| Crab Nebula has a pulsar. Pulsars are rotating neutron stars. They must be neutron stars because other kinds of stars would shatter if they were rotating so fast. Milli-second pulsars to few seconds. |
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Term
| Three White Dwarf Flavors |
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Definition
Hydrogen, Helium, Carbon
This comes about because progenitors of white dwarfs- red giants- lost a fraction of their envelope |
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Term
| Evolution of a white dwarf star |
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Definition
Radiates energy, cools down, and crystallizes.
They freeze as they cool and release latent heat |
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Term
| Multimode pulsations of White Dwarf and the determination of its internal structure |
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Definition
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Term
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Definition
| Pulsations led to the knowledge the white dwarfs can have orbiting planets (Jupiter will survive once the sun goes down) |
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Term
| White Dwarf in a close binary system |
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Definition
| Gas is transferred from companion star to the white dwarf and that gas is compressed and heated to a high temperature leading to thermonuclear explosion classical NOVA! |
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Term
Cataclysmic Variable Stars (CVs)
(Nova mechanism on slide) |
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Definition
| CVs a are binary star systems containing a low-mass main sequence secondary and a white dwarf primary star. Due to the proximity of the stars to each other, the secondary star is distorted into a tear-drop shape. Some CV systems undergo quasi-periodic outbursts. In almost all CV systems, the stars themselves are nearly invisible in telescopes, so the accretion disk is the source of most of the list visible from earth. CVs include systems such as novae, dwarf novae polars, and intermediate polars |
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Term
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Definition
| Inner matter moves more rapidly while outer matter moves more slowly. This creates friction a given parcel of matter accretes onto central star by spiraling slowly inward. Separation is inner Lagrangian Point. |
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Term
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Definition
| White-‐dwarfs in binary systems can gain mass. If (and when)their mass approaches 1.4 Solar Masses- Chandra Mass- the density in the Carbon core is large enough to trigger explosive nuclear burning (degenerate stars the pressure safety value and burn fuel explosively) leading to a very violent explosion- called Supernova Type Ia- that completely destroys the star. |
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Term
| What CVs have White Dwarfs that reach the critical mass limit? |
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Definition
Not classical novae- explosion of surface H shell also rips off a bit of the white dwarf mass- we see excess carbon and oxygen in ejected matter, and a result the white dwarf shrinks in mass rather than grows
Likely outcome in this case- 2nd star finally burns out H, tries to form red giant, mass transfer--> two White Dwarfs |
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Term
| Explosion of a White Dwarf Star (Type Ia) |
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Definition
High density and temperature –deep inside the white dwarf– overcome charge
repulsion– ignite Carbon ⇒ runaway ⇒ total explosion, no neutron star or black hole; these explosions are like a
stick of dynamite.
Core is burned all the way to iron. Only partial burning of C and O in the outer part which leaves O, Mg, Si, S, Ca in outer layers |
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Term
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Definition
Detonation front moves super-‐sonically
(does not give the star time to react)
For detonation alone, the white dwarf would be turned essentially entirely to
iron, and that is Wrong– that is NOT what is seen. |
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Term
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Definition
Deflagration font moves sub-sonically & that allows the outer parts of the white time to expand which quenches nuclear burning.
For deflagration alone, the outer parts of the star are never burned, so substantial unburned carbon and oxygen must be expelled. Careful observation in the infrared show no carbon, so WRONG |
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Term
| Deflagration followed by Detonation |
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Definition
| The detonation catches up with the expanding outer parts, burns everything, gives the right energy, predicts essentially no unburned carbon and oxygen. Matches wide variety of observations |
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Term
| Type Ia Supernovae are "standard candles" |
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Definition
Type Ia provide a way to measure the distances to galaxies.
•Type Ia supernovae all have nearly the same light curves and reach nearly the same brightness because white dwarfs that explode are nearly the same. The small differences can be calibrated.
• Thus we can measure the distance to a Type Ia supernovae accurately by measuring its brightness
• Type Ia supernovae are extremely luminous, so they can be observed in distant galaxies |
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Term
| Type Ia Supernovae Evidence for... |
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Definition
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Term
| Classification of Supernovae |
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Definition
The classification is based on the presence of absence of Hydrogen lines in the spectrum of supernovae.
Type I; No hydrogen lines are present in the spectrum
with sub-category b,c based on the presence of He (b) and absence of it (c)
Type II: Hydrogen lines are present in the spectrum |
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Term
| Comparison of Supernovae different types |
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Definition
On previous slide but look at slide 23 of the second round. Some highlights include:
Type Ib: H envelope lost by stellar win or binary mass transfer, but Helium early
Type Ic: very little Helium, even more mass loss by stellar wind or binary star transfer.
Also Type Ib, Ic, & II are core collapse supernovae as opposed to thermo-nuclear |
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Term
| Supernovae Ia characteristics |
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Definition
In spiral galaxies they tend to avoid the spiral arms because they have had time to drift and are old.
Also in elliptical galaxies where star formation has ceased (once again, old) |
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Term
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Definition
Most occur in spiral galaxies, in the spiral arms where new stars are born (they have had no time to drift from the birth site), sometimes in irregular galaxies, never in elliptical galaxies.
Type II are young short-lived--> iron cores and collapse to neutron star/black hole |
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Term
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Definition
Type Ia is the brightest
Type Ib, Ic similar to Ia but dimmer
Type II remains constant for longer |
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Term
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Definition
Supernovae are rate. 1 per 100 years, last one was in 1658. We are overdue for another
But supernovae leave behind the ejected shells of gas (remnants) our galaxy has many |
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Term
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Definition
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Term
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Definition
Remnant of "Chinese" Guest of 1054.
Even after the death this "star" is ~100,000 times more luminous than the Sun. In about a million years it will fade and become extinguished |
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Term
| Mechanism for the explosion of a star when it core collapses |
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Definition
H->He->Carbon->Oxygen->Irong
Fusion energy
Fission energy |
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Term
| How does the collapse turn into an explosion? Possibility 1 |
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Definition
New-born neutron star over compresses and rebounds
Collapse is halted by repulsive nuclear force (somewhat uncertain) + quantum pressure
Repulsion then attraction then repulsion |
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Term
| How does the collapse turn into an explosion? Possibility 2 |
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Definition
When a neutron star forms, huge amount of potential energy is released from the core of the star shrinking from Earth size to Austin size.
In fact, the energy produced in this collapse is 100 times more than is needed to explode off the outer layers of the massive star- however about 99% of this energy is carried off by neutrinos.
The outer parts of the star, beyond the neutron star, are transparent to the neutrinos, the neutrinos flood out freely and carry off most of the energy.
If 1% of the neutrino energy can be deposited in the outer layers of the star that be sufficient to cause the explosion we see.
The most sophisticated computer calculations seem to find that less than %1 of the neutrino energy can be tapped- thus the question of the mechanism responsible for the explosion of massive stars remains, to this day, unclear. |
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Term
| How does the collapse turn into an explosion? Possibility 3/4? |
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Definition
Perhaps the neutron star can boil out neutrinos at a higher rate... Possible, but still not proven, A bit like boiling a pot on the stove, the steam comes out, but lid just rattles, it does explode to the ceiling
4: Explosion might be triggered by a jet from newly formed black hole |
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Term
| Production of elements in a core collapse supernova |
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Definition
Elements heavier than iron-56 in the periodic table are made during the supernovae.
NI-56 is produced in large quantities in supernovae and is responsible for their spectacularly bright appearance.
The reason is that the initial heat of explosion is diluted away to insignificance as the ejecta expands- expanding gas cools- to a large enough radius from an initial radius, so that photons are able to escape the dense ejecta. |
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Term
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Definition
| Comes from the radioactive decay of nickel-56 to cobalt-56 |
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Term
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Definition
Ejected matter must expand and dilute before photons can stream out and supernova becomes bright (radius~100 x Earth's orbit 10^15 cm)
Type Ia bright than Ib and Ic because Ia has more nickel-56
Type Ib and Ic has same amount of nickel-56 as Type II, but Type II is brighter because of the explosion of the red giant envelope |
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Term
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Definition
| Supernova 1987A in Large Magellanic Cloud. 10^57 neutrinos 19 hit Earth. 170,000 year history |
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