Astronomy intro planets powerpoint

7/28/2019 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



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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
http://casa.colorado.edu/~ajsh/sysbig_gif.html


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The Milky Way Galaxy


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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



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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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Astronomy intro planets powerpoint

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