galaxies and the universe chap. 31 the milky way 31.1 other galaxies in the universe 31.2 cosmology...

Galaxies and the Galaxies and the UniverseUniverseChap. 31Chap. 31Chap. 31Chap. 31

The Milky Way 31.1

Other Galaxies in the Universe 31.2

Cosmology 31.3

The Milky WayThe Milky Way

ObjectivesObjectives

• determine the size and shape of the Milky Way, as well as Earth’s location within it.• describe how the Milky Way formed.

I.I. Discovering the Milky WayDiscovering the Milky WayA.A. Distances to clusters determined Distances to clusters determined

using using variable starsvariable stars..

Stars in the ‘giant’ branch of Stars in the ‘giant’ branch of HR diagram that pulsate in HR diagram that pulsate in brightnessbrightness

Variable StarsVariable Stars



Brightness pulsates between 1.5 hours and 1 dayBrightness pulsates between 1.5 hours and 1 day

1.1. RR Lyrae variablesRR Lyrae variables



Brightness pulsates between 1 and 100 daysBrightness pulsates between 1 and 100 days


2.2. Cepheid variablesCepheid variables

(graph this)(graph this)



The larger the period (time) of pulsation the The larger the period (time) of pulsation the greater the luminosity. greater the luminosity. (graph this)(graph this)


2.2. Cepheid variablesCepheid variables

3.3. These stars make good standard These stars make good standard candlescandles

Calculating distanceCalculating distance

If a star is really bright If a star is really bright (__________ magnitude) but it (__________ magnitude) but it appears to be dim (_________ appears to be dim (_________ magnitude), you know it’s far. magnitude), you know it’s far. The dimmer it looks the farther The dimmer it looks the farther it is.it is.

II.II. Locating the Center of the Locating the Center of the GalaxyGalaxy


A.A. Globular clusters are centered Globular clusters are centered around a point about 28,000 ly awayaround a point about 28,000 ly away



B.B. Center has high density of starsCenter has high density of stars



B.B. Center has high density of starsCenter has high density of stars

C.C. Center is toward Sagittarius Center is toward Sagittarius constellationconstellation

http://www.esa.int

III.III. Shape of Milky WayShape of Milky WayA.A. The MW is a flattened disk shapeThe MW is a flattened disk shape


B.B. Galactic center (nucleus) surrounded Galactic center (nucleus) surrounded by nuclear bulgeby nuclear bulge


B.B. Galactic center (nucleus) surrounded Galactic center (nucleus) surrounded by nuclear bulgeby nuclear bulge

C.C. A spherical-shaped halo containing A spherical-shaped halo containing older stars surrounds the disk.older stars surrounds the disk.

III.III. Shape of Milky WayShape of Milky WayD.D. Four major spiral arms (and Four major spiral arms (and

several minor spiral arms) have several minor spiral arms) have been identifiedbeen identified

IV.IV. Mass of the Milky WayMass of the Milky Way

IV.IV. Mass of the Milky WayMass of the Milky WayA.A. Might be found by measuring Might be found by measuring

luminosityluminosity

Remember that luminosity is related to mass. Remember that luminosity is related to mass. Stars that are bigger are also _________.Stars that are bigger are also _________.



B.B. Mass is usually found by using our Mass is usually found by using our orbital speedorbital speed

Calculating MassCalculating Mass

(M(M11 + M + M22)P)P22 = a = a33 Kepler’s 3 Kepler’s 3rdrd law law

MM11 is sun’s mass (measured in “sun masses”) is sun’s mass (measured in “sun masses”)

MM22 is universe’s mass (measured in “sun masses”) is universe’s mass (measured in “sun masses”)

PP is orbital period (years) = 240 million y is orbital period (years) = 240 million y

aa is distance (in AU) is distance (in AU)

1 ly = 63,200 AU1 ly = 63,200 AU




C.C. Since the MW is about 100 billion Since the MW is about 100 billion times the mass of the Sun, an average times the mass of the Sun, an average sized star, the MW must contain sized star, the MW must contain about about stars. stars.




C.C. Since the MW is about 100 billion Since the MW is about 100 billion times the mass of the Sun, an average times the mass of the Sun, an average sized star, the MW must contain sized star, the MW must contain about about 100 billion100 billion stars. stars.

V.V. Mass of the Center of the Mass of the Center of the Milky WayMilky Way

A.A. Stars near the center orbit Stars near the center orbit center very fast – this indicates center very fast – this indicates a very a very center center


A.A. Stars near the center orbit Stars near the center orbit center very fast – this indicates center very fast – this indicates a very a very massivemassive center center


A.A. Stars near the center orbit Stars near the center orbit center very fast – this indicates center very fast – this indicates a very a very massivemassive center center

B.B. It is thought that there is a It is thought that there is a super black hole at the center of super black hole at the center of our galaxyour galaxy

This center is about 2.6 million times the This center is about 2.6 million times the Sun’s massSun’s mass

VI.VI. Age of Stars in Milky WayAge of Stars in Milky Way

VI.VI. Age of Stars in Milky WayAge of Stars in Milky WayA.A. Young stars form in the arms of Young stars form in the arms of

the MWthe MW

VI.VI. Age of Stars in Milky WayAge of Stars in Milky WayA.A. Young stars form in the arms of Young stars form in the arms of

the MWthe MW

B.B. Old stars are found in the Old stars are found in the halo/nuclear bulge.halo/nuclear bulge.

VII.VII. Formation of Milky WayFormation of Milky Way

VII.VII. Formation of Milky WayFormation of Milky WayA.A. MW was originally round.MW was originally round.

Notice the arrangement of the oldest stars.Notice the arrangement of the oldest stars.

VII.VII. Formation of Milky WayFormation of Milky WayA.A. MW was originally round.MW was originally round.

B.B. The MW cloud collapsed and The MW cloud collapsed and flattened into a disk shape.flattened into a disk shape.

The End

Other Galaxies – 30.2ObjectivesObjectives• Describe how

astronomers classify galaxies

• Identify how galaxies are organized into clusters and superclusters

• Describe the expansion of the universe

I.I. IdentifyingIdentifying

I.I. IdentifyingIdentifyingA.A. Astronomers saw other galaxies Astronomers saw other galaxies

before they knew what they were.before they knew what they were.

I.I. IdentifyingIdentifyingA.A. Astronomers saw other galaxies Astronomers saw other galaxies

before they knew what they were.before they knew what they were.

B.B. Edwin Hubble measured their Edwin Hubble measured their distances to confirm they were distances to confirm they were not in MW.not in MW.

He used variable stars to do it.He used variable stars to do it.

II.II. ClassifyingClassifying

II.II. ClassifyingClassifyingA.A. SpiralSpiral

M74 in pisces

““Cosmic Frisbee”Cosmic Frisbee”


1.1. Normal spirals (S)Normal spirals (S)



2.2. Barred spirals (SB)Barred spirals (SB)

NGC 1300 – in EridanusNGC 1300 – in Eridanus


Type aType a represents tightly wound arm with bright represents tightly wound arm with bright nucleus.nucleus.


2.2. Barred spirals (SB)Barred spirals (SB)

3.3. These are further divided by These are further divided by how tightly wound arms are (a, how tightly wound arms are (a, b, c)b, c)


B.B. EllipticalsEllipticals

““Cosmic Football”Cosmic Football”


B.B. EllipticalsEllipticals1.1. Divided from E0 to E7.Divided from E0 to E7.


B.B. EllipticalsEllipticals1.1. Divided from E0 to E7.Divided from E0 to E7.

2.2. E7 has a large ratio of major E7 has a large ratio of major axis/minor axis, E0 is circular.axis/minor axis, E0 is circular.


B.B. EllipticalsEllipticals

C.C. Irregular Galaxies (Irr)Irregular Galaxies (Irr)

http://www.nasa.gov

II.II. ClassifyingClassifyingD.D. MassesMasses


1.1. Dwarf ellipticals have few stars Dwarf ellipticals have few stars (about 1 million).(about 1 million).



2.2. Large spirals, like MW, have Large spirals, like MW, have about 100 million stars.about 100 million stars.



2.2. Large spirals, like MW, have Large spirals, like MW, have about 100 million stars.about 100 million stars.

3.3. Giant ellipticals have mass of 100 Giant ellipticals have mass of 100 trillion trillion xx the sun. the sun.

III.III. Groups & ClustersGroups & Clusters

III.III. Groups & ClustersGroups & ClustersA.A. Local groupLocal group

M33 - M33 - member of the local groupmember of the local group


1.1. Includes Milky WayIncludes Milky Way

A.A. Local groupLocal group

http://www.spacetoday.org



2.2. About 35 known members About 35 known members including Andromeda and including Andromeda and several dwarf galaxies.several dwarf galaxies.


http://www.via.ee



2.2. About 35 known members About 35 known members including Andromeda and including Andromeda and several dwarf galaxies.several dwarf galaxies.

3.3. It’s about 2 million ly acrossIt’s about 2 million ly across



B.B. There are clusters much bigger There are clusters much bigger than local group (ex. Virgo)than local group (ex. Virgo)

http://www.randybrewer.net


B.B. There are clusters much bigger There are clusters much bigger than local group (ex. Virgo)than local group (ex. Virgo)

C.C. Mass of clusters are bigger than Mass of clusters are bigger than the sum of the parts.the sum of the parts.

This is evidence for existence of dark matterThis is evidence for existence of dark matter

IV.IV. The Expanding UniverseThe Expanding Universe

IV.IV. The Expanding UniverseThe Expanding UniverseA.A. Discovered by Hubble in 1929Discovered by Hubble in 1929


B.B. ““Red shift”Red shift”

Light waves are stretched out due to relative motion Light waves are stretched out due to relative motion of source and observer away from each other.of source and observer away from each other.

Red ShiftRed Shift


B.B. ““Red shift”Red shift”1.1. Indicates galaxy is moving away Indicates galaxy is moving away

from usfrom us



from usfrom us

2.2. Hubble determined the degree of Hubble determined the degree of red shift depends on the distance red shift depends on the distance awayaway



from usfrom us

2.2. Hubble determined the degree of Hubble determined the degree of red shift depends on the distance red shift depends on the distance awayaway

3.3. All galaxies are moving away All galaxies are moving away from all other galaxies (not just from all other galaxies (not just Earth)Earth)



C.C. Hubble’s lawHubble’s law

vv = = HdHd



C.C. Hubble’s lawHubble’s law

vv = = HdHdvelocity (km/s)velocity (km/s)

Distance (Mpc)Distance (Mpc)

Hubble’s constantHubble’s constant

V.V. Active GalaxiesActive Galaxies

V.V. Active GalaxiesActive GalaxiesA.A. Radio GalaxiesRadio Galaxies

NGC 5128 - NGC 5128 - Radio galaxyRadio galaxy


1.1. Two lobes connected by jets of Two lobes connected by jets of hot gas.hot gas.


1.1. Two lobes connected by jets of Two lobes connected by jets of hot gas.hot gas.

2.2. Observed by radio telescopes Observed by radio telescopes because they emit more radio because they emit more radio waves than visible light.waves than visible light.

Radio telescope

V.V. Active GalaxiesActive GalaxiesB.B. Active Galactic Nuclei (AGN)Active Galactic Nuclei (AGN)


1.1. Highly energetic galactic coresHighly energetic galactic cores


1.1. Highly energetic galactic coresHighly energetic galactic cores

2.2. Output of energy variesOutput of energy varies

VI.VI. QuasarsQuasars

VI.VI. QuasarsQuasarsA.A. Like other galaxies, but these are Like other galaxies, but these are

strong radio emitters.strong radio emitters.



B.B. Create emission lines, instead of Create emission lines, instead of absorption lines.absorption lines.

Absorption spectrumAbsorption spectrum

Emission spectrumEmission spectrum



B.B. Create emission lines, instead of Create emission lines, instead of absorption lines.absorption lines.

C.C. These objects have a very large These objects have a very large red shift (so they are very far red shift (so they are very far away).away).

VII.VII. Looking back in timeLooking back in time

VII.VII. Looking back in timeLooking back in timeA.A. We study stars/galaxies as they We study stars/galaxies as they

were.were.

VII.VII. Looking back in timeLooking back in timeA.A. We study stars/galaxies as they We study stars/galaxies as they

were.were.

B.B. Seeing quasars that are very far Seeing quasars that are very far (old) suggests a possible ‘quasar (old) suggests a possible ‘quasar stage’ during universe history.stage’ during universe history.

The End

Cosmology – 31.3ObjectivesObjectives• Explain the different

theories about the formation of the universe

• Describe the possible outcomes of universal expansion

I.I. ModelsModels

I.I. ModelsModelsA.A. Steady State TheorySteady State Theory


1.1. The Universe does not change The Universe does not change with time.with time.



2.2. The Universe had no beginningThe Universe had no beginning




3.3. The Density stays constantThe Density stays constant




3.3. The Density stays constantThe Density stays constant

4.4. As Universe expands, new As Universe expands, new material is created and addedmaterial is created and added

I.I. ModelsModelsB.B. Big Bang TheoryBig Bang Theory


1.1. All matter began at a point initiallyAll matter began at a point initially


1.1. All matter began at a point initiallyAll matter began at a point initially

2.2. The matter and space of our Universe The matter and space of our Universe has been expanding ever sincehas been expanding ever since

II.II. Cosmic Background Cosmic Background Radiation (CBR)Radiation (CBR)

II.II. Cosmic Background Cosmic Background Radiation (CBR)Radiation (CBR)A.A. Low-level microwave radiationLow-level microwave radiation


B.B. This radiation comes from all This radiation comes from all directionsdirections



C.C. CBR is associated with cool CBR is associated with cool temperature (2.735 K)temperature (2.735 K)



C.C. CBR is associated with cool CBR is associated with cool temperature (2.735 K)temperature (2.735 K)

D.D. The steady state theory does not The steady state theory does not explain CBRexplain CBR

II.II. Cosmic Background Cosmic Background Radiation (CBR)Radiation (CBR)E.E. This has been mapped by This has been mapped by

satellites.satellites.

III.III. Big Bang ModelBig Bang Model

III.III. Big Bang ModelBig Bang ModelA.A. Momentum carries material Momentum carries material

outward while outward while pulls inward pulls inward


outward while outward while gravitygravity pulls inward pulls inward



B.B. The rate of expansion is slowingThe rate of expansion is slowing




C.C. Possible OutcomesPossible Outcomes





1.1. Open Universe –Open Universe –

Expansion of Universe never stopsExpansion of Universe never stops






2.2. Closed Universe – Closed Universe –

Expansion stops and becomes a contractionExpansion stops and becomes a contraction






2.2. Closed Universe – Closed Universe –

3.3. Flat Universe – Flat Universe –

Expansion slows to halt in infinite amt. of timeExpansion slows to halt in infinite amt. of time

III.III. Big Bang ModelBig Bang ModelD.D. Critical DensityCritical Density

1.1. The outcome of the Universe The outcome of the Universe depends on the amount (density) of depends on the amount (density) of material in it.material in it.



a)a) Less than critical density (10Less than critical density (10-26-26 kg/mkg/m33) results in ) results in open Universe.open Universe.




b)b) More than critical density More than critical density means means closed Universeclosed Universe




b)b) More than critical density More than critical density means means closed Universeclosed Universe

c)c) Equal to Critical density means Equal to Critical density means flat Universeflat Universe



d)d) Observations show less than Observations show less than critical density, (but there is critical density, (but there is dark matterdark matter))

IV.IV. Decrease of Rate of Decrease of Rate of ExpansionExpansion


A.A. This could be used to tell the This could be used to tell the outcome of the Universeoutcome of the Universe



B.B. Universe’s expansion should be Universe’s expansion should be getting slowergetting slower



B.B. Universe’s expansion should be Universe’s expansion should be getting slowergetting slower

C.C. We observed it’s actually We observed it’s actually expanding fasterexpanding faster

IV.IV. Inflationary UniverseInflationary Universe

Universe began with a fluctuation in expansion. Universe began with a fluctuation in expansion. For a brief instant its rate of expansion increasedFor a brief instant its rate of expansion increased

Calculating AgeCalculating Age

Calculate the number of years since Calculate the number of years since expansion of the Universe using expansion of the Universe using Hubble’s constant: 1/H = timeHubble’s constant: 1/H = time

H = 50 km/s / Mpc or H = 100 km/s / MpcH = 50 km/s / Mpc or H = 100 km/s / Mpc

1 pc = 3.1 x 101 pc = 3.1 x 101313 km km

‘‘mega’ (M) = 1 000 000 unitsmega’ (M) = 1 000 000 units

The End

galaxies and the universe chap. 31 the milky way 31.1 other galaxies in the universe 31.2 cosmology...

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