astronomy intro planets powerpoint
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High Mass Stellar Death
Part 3: Stars
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Review of low-mass stars7- main sequence
H fusion in core8- red giant
H fusion in shell9- helium flashHe fusion starts in core
10- horizontal branchHe fusion continues
11- asymptotic giant branch
H and He fusion in shells12 - planetary nebulaOuter envelope lost
13- white dwarf
stellar remnant
7
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Stellar Evolution
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Even without nuclear reactions,
Stars get h o tte r inside as they radiate!
T temporarily reduced reduces pressure
the star contracts
converts gravitational energy into heat
the center of the star gets hotter
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Massive starsMass > 8 solar masses
1st stages same as low massMS
shell H fusioncore He fusionshell H and He fusion
After H and He shell fusiondifferent steps
Massive Stars
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fuse C in core run out of C shell fusion - H, He, C oxygen fusion in core runs out of O shell fusion - H, He, C, O...
silicon fusion in core (ash of Si fusion is iron) run out of Si, start shell fusion left with iron core and multiple shells
What happens next ?
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Nuclear Reactions in a 15-M Star
T > 100 million K in the core,He Be Carbon;
T > 600 million K,Carbon Oxygen, Neon, Magnesium
Silicon, Sulfur, etc.;
T > 3 billion K,Sulfur Iron .
The iron core is inert.Neither fusion nor fission of ironproduces energy.
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Ignition of metals iron core
27
3
6 826
92
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The iron core has no further energysource via nuclear reactions
central temperature rises.
At ~ 10 billion K photodisintegration! when high energy gamma rays excite a nucleus
and it breaks apart in nuclear fission This uses up energy (= heat)!
The iron core is suddenly refrigerated.
Pressure disappears.
The core collapses in less than a second.
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Core Collapse Supernova Cannot fuse iron - star has no fuel supply
core collapses and temperature in core increases Photodisintergration: iron atoms broken into protons,
neutrons, and electrons
Neutronization: convert electrons and protons intoneutrons and neutrinos
Core collapse halted by neutron degeneracy pressure
=> Core bounce Envelope of star lifted off : Type II supernovaVery luminous exploding star Fades over weeks or months
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Stage Central temperature Central density Duration(K) (kg/m 3) of stage
Hydrogen burning 4. 10 7 4 10 3 7 10 6 yearsHelium burning 2. 10 8 7 10 5 5 10 5 yearsCarbon burning 6. 10 8 2 10 8 600 years
Neon burning 1.2 10 9 4 10 9 1 year Oxygen burning 1.5 10 9 1 10 10 6 monthsSilicon * burning 2.7 10 9 3 10 10 1 day
*more than a solar mass!
Result: a slowly contracting iron core in which T increases.
Evolutionary Stages of a 25-M Star
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Stage Central temperature Central density Duration(K) (kg/m 3) of stage
Hydrogen burning 4. 10 7 4 10 3 7 10 6 yearsHelium burning 2. 10 8 7 10 5 5 10 5 yearsCarbon burning 6. 10 8 2 10 8 600 years
Neon burning 1.2 10 9 4 10 9 1 year Oxygen burning 1.5 10 9 1 10 10 6 monthsSilicon * burning 2.7 10 9 3 10 10 1 dayCore collapse 5.4 10 9 3 10 12 0.2 secondsCore bounce 2.3 10 10 4 10 17 millisecondsExplosion ~ 10 9 varies 10 seconds
*more than a solar mass!
Evolutionary Stages of a 25-M Star
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Type II Supernova
In less time than it takes to snap your fingers,
10 46 joules come out, 99% as neutrinos.
1 joule =
energy required to lift a small apple 1 m in Earth's gravity
amount of heat a quiet person produces every 1/100th of a sec
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In less time than it takes to snap your fingers,
10 46 joules come out, 99% as neutrinos.
10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
The Sun would have to shine for ~ 800 bil l ion years at its present luminosity to give off 10 46 joules.
At the moment of collapse, the power output of a Type IISupernova is comparable to that of all the stars
in the observed Universe com bined.
Type II Supernova
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Evolution into a Supernova
Type IISupernova
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Supernova Remnants Debris of supernova explosions
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SN 1987A
First naked-eye SN in 383 years
inner ring = gas ejected by the star 20,000 years ago and now lit upby the blast.
The outer rings are not understood.
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SN 1994A in UGC 8214
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Crab Nebula (1054 AD)
( ld)
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Cygnus Loop (~ 20000 years old)
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Supernova Remnant N132D (x-rays)
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Keplers Supernova Remnant
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Supernova 1066
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Recent Supernovae In Our Galaxy
Supernovae happen in our Galaxy ~ once per human generation.
Most of them are not seen because of dust absorption.
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In the expanding SN shock wave,nuclear reactions go berserk
cook up elements more
massive than iron
All iron was expelled by supernovae.
All elements heavier than iron weremanufactured in supernovaexplosions.
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Tychos Supernova
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Supernovae Light Curves
SN I get about 2 magnitudes more luminous than SN II.
Supernova light curves: Type I brightness decreases quickly and smoothly.
Type II light curve more complicated , (energy from explosion,
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Supernova 1987A in the Large Magellanic Cloud
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Supernovae of Type I and II
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White Neutron Black dwarf star hole
Progenitor star mass: 0.08 8 M 8 20 M >20 M Corpse mass: 1.4 M 3 M 3 10 M Corpse radius: 7000 km ~ 10 km ~ 10 km Corpse density: 10 6 g cm -3 10 15 g cm -3 -
1 teaspoonful on Earth: 5 tons 1 billion tons -Thickness of atmos here: ~ 50 km a few meters -
Corpses of Stars
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Neutron Stars
rigid crust ~ 100 m thick with somesuperconducting material
interior = free neutrons
core density > nuclear densities!
supported by neutron degeneracy pressure
spin many times/svery strong magnetic fields
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Neutron Stars
masses are 1.4 to 3 solar masses
Recall core bounce drives ejection of envelope Core stays intact During core collapse neutronization occurred
core made mostly of neutrons
neutron star
End state of stellar evolution for stars 8 - 25 solar masses
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How is a neutron star supported?
No fusion - cant be just thermal pressure Neutron degeneracy pressure
Pauli exclusion principle:2 identical particles cannot be in the same energy state.
In core cram neutrons together Resist being pushed together Exert pressure outward
Neutron degeneracy pressure
Pulsars = rotating magnetized neutron stars
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Pulsars = rotating, magnetized neutron stars
Crab Nebula Pulsar
powerful electromagnetic fields beams of radiation (lighthouse)
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A Pulsar
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PulsarsDetected radio sources that varied regularly
Called pulsars Period of pulses 0.2 - 1.5 seconds
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Crab Nebula (1054 AD)
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Spinning Neutron Star
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Pulsars = Neutron StarsPulsars are rapidly rotating
neutron starsFound pulsar in the Crab
Nebula (a SN remnant)
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Strong magnetic fields beam light
Light house model see pulsar only when beam point towards us
Period of pulses = rotation period of neutron star
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Pulsar Oddities
sur face gravi ty i s VERY high ! 150 pound person = a million tonspulsars highest mountains = mm high
can sp in VERY fast!
fastest has period of 0.0014 s star spins 642 times/sdozens of m il li second pu l sa r s known
f i r s t p lane ts o uts ide o ur Solar Sys tem discovered orbiting a pulsar VERY UNEXPECTED!
Pulsar Planets
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Pulsar Planets
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White Neutron Black dwarf star hole
Progenitor star mass: 0.08 8 M 8 20 M >20 M Corpse mass: 1.4 M 3 M 3 10 M Corpse radius: 7000 km ~ 10 km ~ 10 km Corpse density: 10 6 g cm -3 10 15 g cm -3 -1 teaspoonful on Earth: 5 tons 1 billion tons -Thickness of atmosphere: ~ 50 km a few meters -
Corpses of Stars
Hypernovacreates
Supernovacreates
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2r GMm F
High-gravityplanet
(small r)
Surface gravity 1/radius 2
Black Hole
Medium-gravityplanet
r
m
m
m
mass M
M
M
Black Hole : so smallsurface gravity so high
nothing can escape(not even light!)
r 2 GM
c2
Low-gravity planet(big r)
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2r GMm F
Could we turn the Earth into a black hole?
To turn the Earth into a black hole,
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o tu t e a t to a b ac o e,we would have to squeeze it into the size of a grape.
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sp eed o f light
i s con s tan t
It is independent of the motionof observer or emitter.
So: Light that is fighting gravity does no t slow down;
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g g g g yit is r e d s h if te d and gets bent
radius of photon sphere
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Black Hole
Once the core has shrunkinside its gravitational
radius, nothing can prevent it from collapsing to asingularity (size = 0)!
Sun
Sch
3
M km
M r
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All physical laws
break downat a singularity.
A bl k h l h h i
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A black hole has no hair.
Mass
Charge
Bl k H l NOT C i V Cl !
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Black Holes are NOT Cosmic Vacuum Cleaners!
Black holes have MASS.
So black holes have a certain amount of GRAVITY.
BUT NOT MORE GRAVITY than any other object with the same mass!
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Einsteins general relativity
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ijijij T G g R R 821
Ricci tensor
(space-time curvature)
Ricci scalar(coordinate transformation)
Coordinate system
Gravitationalconstant
Energy momentum
tensor (mass)
Einsteins equations of motion
Black Holes are NOT Cosmic Vacuum Cleaners!
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Black Holes are NOT Cosmic Vacuum Cleaners!
Event horizon
Size of EarthSize of
Earths Orbit
Edge of solar system
1 parsec
6500 km / s
42 km / s
4 km / s
92 m / s
NOT TO SCALE Black holes do notsuck in the unwaryany more than doother gravitatingobjects.
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General relativity
Gravity CURVES space-time
Gravity SLOWS DOWN clocks (time dilation)
Falling into a black hole:From someone observing far away ...
Object gets closer to the event horizon and its clocks slow down. Radiationcoming from the object gets redder.The object never goes through the event horizon.
From the object going into it ...
Tidal forces stretch the object and eventually break it into a chain of elementary particles that eventually reach the singularity.
D Bl k H l E i t?
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It is likely that very massive black holes exist at the centers of most galaxies.
Black holes of a few solar masses are believed to form when massive stars undergocore collapse if the collapsed core exceeds the maximum of ~ 3 M permitted for neutron stars. The best evidence for such black holes comes from binary stars.
Single-line spectroscopic binaries
Some stars have spectral lines which shift back and forth periodically. Most suchsystems exhibit two sets of lines, one from each star, but in others we cannot detectany light from one of the stars. If the dark star has a mass greater than 3 M , thenit may be a black hole.
Irregular X-ray sources
Just like a neutron star, a black hole can attract matter from an ordinary star. Thismatter settles into an accretion disk around the hole and slowly spirals in, radiatingX-rays as it does so. Cygnus X-1 is the black hole candidate. Its X-rays areemitted from the vicinity of an object with a mass of 5 to 10 M and a diameter of less than 300 km. Such an object is almost certainly a black hole.
Do Black Holes Exist?
Do Black Holes E ist?
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Very massive black holes:
centers of most galaxies
Stellar mass black holes: evidence from binary stars
Single-line spectroscopic binariesBinary X-ray sources
Do Black Holes Exist?
SS 433
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SS 433
Location of
binary system
Scale: 1000 times the Sun-Earth distance
Gas from this X-raybinary is coming out at
0.25c!
The engine may be ablack hole.
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Approaching a Black Hole
Dr. Andrew Hamilton, UC Boulder
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The Milky Way Galaxy
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The Milky Way Galaxy
f lat dis k of ~ 200 billion stars + gasembedded in sph erical halo of stars, globular clusters, and dark material
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Properties of our Galaxy
Diameter of disk ~ 100,000 lyDiameter of halo ~ 300,000 lyNumber of stars ~ 10 11 Total mass ~ 10 12 M
Age ~13 10 9 y
Suns distance from the center ~ 30,000 lySuns orbital velocity ~ 220 km / s
Suns orbital period ~ 250 million y
The Milky Way Galaxy
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The Milky Way Galaxy
The Milky Way Galaxy
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The Milky Way Galaxy
Vega
AndromedaGalaxy
Pleiades
SmallMagellanic Cloud
Large MagellanicCloud
CanopusSirius
Orion
Our Galaxy: Portrait by Jon Lomberg
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y y g
Our Galaxy
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y
Our Sun
The Solar Neighborhood
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The Solar Neighborhood
30 closest stars to the Sun
typical separation:~ 1 pc~ 200,000 AU
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What would you see from here?
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What would you see from here?
Sun
Immanuel Kants Hypothesis (1755)
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We see the Milky Way as a diffuse band of light encircling the sky.Galileo : this light comes from countless faint stars
Immanuel Kant: flat, spinning disk of stars viewed from withinother nebulae = island universes strewn through space; appearance
depends on orientation
yp ( )
Sun
few stars
many stars
Problems with Dust
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visibility in the plane of the disk is limited to a few thousand parsecs (kpc)
Shapleys Discovery
distances to globular clusters 3-D distribution
center point about 8.5 kpc (30,000 ly) from the Sun = true center of theMilky Way
Visible partof disk
Globular clusters
Disk
The Multiwavelength Milky Way
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The Multiwavelength Milky Way
Our Galaxy at Different Wavelengths
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y g
Our Galaxy in Infrared Light (COBE)
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y g ( )
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Cold Gas Traces Spiral Structure
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p
Hydrogen atoms
Molecular Clouds
Highly idealized model
The Sun
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What would you expect to find at the Galactic Center?
At the center
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At the center
Galactic nucleus =Sagittarius A*
Kormendy 2000, Nature, 407, 307
The Structure of Our Galaxy
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The Mass of Our Galaxy
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Do we have a photograph of our galaxy from the outside?
Milky Way Analogues
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NGC 1232 NGC 891
Other Galaxies
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If people were stars, cities would be galaxies.
galaxy: a large cluster of stars, gas, and dark matter held together by gravity
Typical galaxy masses: 10 7 to 10 13 M Typical galaxy diameters: 1000 to 500,000 ly
Star Map
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p
M31The AndromedaGalaxy
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The Discovery of Galaxies
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In the early 1900s, people understood that many nebulae are in our Galaxy.
everything is in our Galaxy some nebulae are islanduniverses outside our Galaxy
vs.
Hubble measured distance to M31 using C h id V i bl
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Cepheid Variables
VariableWhite Dwarfs
Some stars are unstable: theypulsate in radius and brightness .
Period-Luminosity Relation:Cepheids with higher average luminosities
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pulsate with longer periods!
- we know apparent magnitude- observe Cepheid period to get absolute magnitude distance
Light curve of Cephei
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Cepheid variable stars in M31(From Hubbles The Realm of the Nebulae)
Edwin Hubble
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Intermediates between S and SB exist.
Irregulars
Elliptical Galaxies
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M 87Ellipticals
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Can you think of something thats the same shape as anelliptical galaxy?
Elliptical Galaxies
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M 87
Ellipsoidselongation = round to flattened
(mostly because different orientations) no structural details
orbits: very 3-Dlittle net rotationlarge random motions
most stars are old (Pop II)
Elliptical Galaxies
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sometimes contain thousands of globular clusters
M 87
NGC 720 (E)
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Spiral Galaxies
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M 51Spirals
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Can you think of something thats the same shape as aspiral galaxy?
Spiral Galaxies
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disk of stars and gas
spiral structureflatlarge range of stellar agesorbits almost in a single plane
disks rotaterandom motions are small
+
Sa and Sb: central bulge small elliptical
Pop. II (old) starsM 51
Spiral Galaxies
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Sa Scbulge contribution decreases,
fractional amount of gas increases,young stars contribution increases, sodisk looks more patchy, andspiral arms become more open
The Milky Way
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Type Scor
SBc
Spiral Galaxies
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the wind ing p rob lem
Spiral Galaxies
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M 51
sp i ral a rm s are dens i ty w aves
pattern rotates rigidly stars, gas flow through waves gas compression in wave triggers star formation
NGC 4594 (Sa)
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NGC 4826 (Sab)
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M 81 (Sab) and M 82 (Irr)
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M 31 (Sb) and M 32 (E)
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NGC 4565 (Sb)
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NGC 891 (Sbc)
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M 33 (Sc)
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M 74 (Sc)
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M 83 (SBb)
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NGC 1365 (SBb)
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NGC 1300 (SBbc)
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i t di t b t E d S
S0 Galaxies
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intermediate between E and S disks, but no spiral structure
NGC 5866 S0
NGC 5866
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Irregular Galaxies asymmetric, messy, no bulge
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asymmetric, messy, no bulge mostly Pop I stars (young)
large amounts of cool gas
Sextans A
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NGC 6822 (Irr)
Galaxies group together
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Milky Way and Andromeda Galaxy: two largest members of our Local Group .
- Nearby clusters of galaxies- Clusters of clusters = superclusters .- Void s = spaces between superclusters.
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Seyferts Sextet
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Hickson Compact Group 87
We live in the suburbs of the Virgo Cluster.The Virgo Cluster is in the suburbs of the Great Attractor.
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You are here
Local Void
Coma Cluster
Great Attractor
Perseus-PiscesSupercluster
Galaxy density
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Coma Cluster of Galaxies
The Nearby Universe
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