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Galaxies and the Universe. The Milky Way 31.1 Other Galaxies in the Universe 31.2 Cosmology 31.3. Chap. 31. Objectives. The Milky Way. determine the size and shape of the Milky Way, as well as Earth’s location within it. describe how the Milky Way formed. Discovering the Milky Way.

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galaxies and the universe

Galaxies and the Universe

The Milky Way 31.1

Other Galaxies in the Universe 31.2

Cosmology 31.3

Chap. 31

the milky way

Objectives

The Milky Way

  • determine the size and shape of the Milky Way, as well as Earth’s location within it.
  • describe how the Milky Way formed.
slide3

Discovering the Milky Way

  • Distances to clusters determined using variable stars.
slide4

Discovering the Milky Way

  • Distances to clusters determined using variable stars.
slide5

Variable Stars

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

slide6

Discovering the Milky Way

  • Distances to clusters determined using variable stars.
  • RR Lyrae variables

Brightness pulsates between 1.5 hours and 1 day

slide7

Discovering the Milky Way

  • Distances to clusters determined using variable stars.
  • RR Lyrae variables
  • Cepheid variables

(graph this)

Brightness pulsates between 1 and 100 days

slide8

Discovering the Milky Way

  • Distances to clusters determined using variable stars.
  • RR Lyrae variables
  • Cepheid variables
  • These stars make good standard candles

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

slide9

Calculating distance

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

slide11

Locating the Center of the Galaxy

  • Globular clusters are centered around a point about 28,000 ly away
slide12

Locating the Center of the Galaxy

  • Globular clusters are centered around a point about 28,000 ly away
  • Center has high density of stars
slide13

Locating the Center of the Galaxy

  • Globular clusters are centered around a point about 28,000 ly away
  • Center has high density of stars
  • Center is toward Sagittarius constellation

http://www.esa.int

slide14

Shape of Milky Way

  • The MW is a flattened disk shape
slide15

Shape of Milky Way

  • The MW is a flattened disk shape
  • Galactic center (nucleus) surrounded by nuclear bulge
slide16

Shape of Milky Way

  • The MW is a flattened disk shape
  • Galactic center (nucleus) surrounded by nuclear bulge
  • A spherical-shaped halo containing older stars surrounds the disk.
slide17

Shape of Milky Way

  • Four major spiral arms (and several minor spiral arms) have been identified
slide19

Mass of the Milky Way

  • Might be found by measuring luminosity

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

slide20

Mass of the Milky Way

  • Might be found by measuring luminosity
  • Mass is usually found by using our orbital speed
slide21

Calculating Mass

(M1 + M2)P2 = a3 Kepler’s 3rd law

M1 is sun’s mass (measured in “sun masses”)

M2 is universe’s mass (measured in “sun masses”)

P is orbital period (years) = 240 million y

a is distance (in AU)

1 ly = 63,200 AU

slide22

Mass of the Milky Way

  • Might be found by measuring luminosity
  • Mass is usually found by using our orbital speed
  • Since the MW is about 100 billion times the mass of the Sun, an average sized star, the MW must contain about stars.
slide23

Mass of the Milky Way

  • Might be found by measuring luminosity
  • Mass is usually found by using our orbital speed
  • Since the MW is about 100 billion times the mass of the Sun, an average sized star, the MW must contain about 100 billion stars.
slide24

Mass of the Center of the Milky Way

  • Stars near the center orbit center very fast – this indicates a very center
slide25

Mass of the Center of the Milky Way

  • Stars near the center orbit center very fast – this indicates a very massive center
slide26

Mass of the Center of the Milky Way

  • Stars near the center orbit center very fast – this indicates a very massive center
  • It is thought that there is a super black hole at the center of our galaxy

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

slide28

Age of Stars in Milky Way

  • Young stars form in the arms of the MW
slide29

Age of Stars in Milky Way

  • Young stars form in the arms of the MW
  • Old stars are found in the halo/nuclear bulge.
slide31

Formation of Milky Way

  • MW was originally round.

Notice the arrangement of the oldest stars.

slide32

Formation of Milky Way

  • MW was originally round.
  • The MW cloud collapsed and flattened into a disk shape.
other galaxies 30 2

Objectives

Other Galaxies – 30.2

  • Describe how astronomers classify galaxies
  • Identify how galaxies are organized into clusters and superclusters
  • Describe the expansion of the universe
slide36

Identifying

  • Astronomers saw other galaxies before they knew what they were.
slide37

Identifying

  • Astronomers saw other galaxies before they knew what they were.
  • Edwin Hubble measured their distances to confirm they were not in MW.

He used variable stars to do it.

slide39

Classifying

  • Spiral

M74 in pisces

“Cosmic Frisbee”

slide40

Classifying

  • Spiral
  • Normal spirals (S)
slide41

Classifying

  • Spiral
  • Normal spirals (S)
  • Barred spirals (SB)

NGC 1300 – in Eridanus

slide42

Classifying

  • Spiral
  • Normal spirals (S)
  • Barred spirals (SB)
  • These are further divided by how tightly wound arms are (a, b, c)

Type a represents tightly wound arm with bright nucleus.

slide43

Classifying

  • Spiral
  • Ellipticals

“Cosmic Football”

slide44

Classifying

  • Spiral
  • Ellipticals
  • Divided from E0 to E7.
slide45

Classifying

  • Spiral
  • Ellipticals
  • Divided from E0 to E7.
  • E7 has a large ratio of major axis/minor axis, E0 is circular.
slide46

Classifying

  • Spiral
  • Ellipticals
  • Irregular Galaxies (Irr)

http://www.nasa.gov

slide48

Classifying

  • Masses
  • Dwarf ellipticals have few stars (about 1 million).
slide49

Classifying

  • Masses
  • Dwarf ellipticals have few stars (about 1 million).
  • Large spirals, like MW, have about 100 million stars.
slide50

Classifying

  • Masses
  • Dwarf ellipticals have few stars (about 1 million).
  • Large spirals, like MW, have about 100 million stars.
  • Giant ellipticals have mass of 100 trillion x the sun.
slide52

Groups & Clusters

  • Local group

M33 -

member of the local group

slide53

Groups & Clusters

  • Local group
  • Includes Milky Way

http://www.spacetoday.org

slide54

Groups & Clusters

  • Local group
  • Includes Milky Way
  • About 35 known members including Andromeda and several dwarf galaxies.

http://www.via.ee

slide55

Groups & Clusters

  • Local group
  • Includes Milky Way
  • About 35 known members including Andromeda and several dwarf galaxies.
  • It’s about 2 million ly across
slide56

Groups & Clusters

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

http://www.randybrewer.net

slide57

Groups & Clusters

  • Local group
  • There are clusters much bigger than local group (ex. Virgo)
  • Mass of clusters are bigger than the sum of the parts.

This is evidence for existence of dark matter

slide59

The Expanding Universe

  • Discovered by Hubble in 1929
slide60

The Expanding Universe

  • Discovered by Hubble in 1929
  • “Red shift”

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

slide62

The Expanding Universe

  • Discovered by Hubble in 1929
  • “Red shift”
  • Indicates galaxy is moving away from us
slide63

The Expanding Universe

  • Discovered by Hubble in 1929
  • “Red shift”
  • Indicates galaxy is moving away from us
  • Hubble determined the degree of red shift depends on the distance away
slide64

The Expanding Universe

  • Discovered by Hubble in 1929
  • “Red shift”
  • Indicates galaxy is moving away from us
  • Hubble determined the degree of red shift depends on the distance away
  • All galaxies are moving away from all other galaxies (not just Earth)
slide65

The Expanding Universe

  • Discovered by Hubble in 1929
  • “Red shift”
  • Hubble’s law

v = Hd

slide66

The Expanding Universe

  • Discovered by Hubble in 1929
  • “Red shift”
  • Hubble’s law

v = Hd

Distance (Mpc)

velocity (km/s)

Hubble’s constant

slide68

Active Galaxies

  • Radio Galaxies
slide69

Active Galaxies

  • Radio Galaxies
  • Two lobes connected by jets of hot gas.

NGC 5128 -

Radio galaxy

slide70

Active Galaxies

  • Radio Galaxies
  • Two lobes connected by jets of hot gas.
  • Observed by radio telescopes because they emit more radio waves than visible light.

Radio telescope

slide71

Active Galaxies

  • Active Galactic Nuclei (AGN)
slide72

Active Galaxies

  • Active Galactic Nuclei (AGN)
  • Highly energetic galactic cores
slide73

Active Galaxies

  • Active Galactic Nuclei (AGN)
  • Highly energetic galactic cores
  • Output of energy varies
slide75

Quasars

  • Like other galaxies, but these are strong radio emitters.
slide76

Quasars

  • Like other galaxies, but these are strong radio emitters.
  • Create emission lines, instead of absorption lines.

Absorption spectrum

Emission spectrum

slide77

Quasars

  • Like other galaxies, but these are strong radio emitters.
  • Create emission lines, instead of absorption lines.
  • These objects have a very large red shift (so they are very far away).
slide79

Looking back in time

  • We study stars/galaxies as they were.
slide80

Looking back in time

  • We study stars/galaxies as they were.
  • Seeing quasars that are very far (old) suggests a possible ‘quasar stage’ during universe history.
cosmology 31 3

Objectives

  • Explain the different theories about the formation of the universe
  • Describe the possible outcomes of universal expansion

Cosmology – 31.3

slide84

Models

  • Steady State Theory
slide85

Models

  • Steady State Theory
  • The Universe does not change with time.
slide86

Models

  • Steady State Theory
  • The Universe does not change with time.
  • The Universe had no beginning
slide87

Models

  • Steady State Theory
  • The Universe does not change with time.
  • The Universe had no beginning
  • The Density stays constant
slide88

Models

  • Steady State Theory
  • The Universe does not change with time.
  • The Universe had no beginning
  • The Density stays constant
  • As Universe expands, new material is created and added
slide89

Models

  • Big Bang Theory
slide90

Models

  • Big Bang Theory
  • All matter began at a point initially
slide91

Models

  • Big Bang Theory
  • All matter began at a point initially
  • The matter and space of our Universe has been expanding ever since
slide93

Cosmic Background Radiation (CBR)

  • Low-level microwave radiation
slide94

Cosmic Background Radiation (CBR)

  • Low-level microwave radiation
  • This radiation comes from all directions
slide95

Cosmic Background Radiation (CBR)

  • Low-level microwave radiation
  • This radiation comes from all directions
  • CBR is associated with cool temperature (2.735 K)
slide96

Cosmic Background Radiation (CBR)

  • Low-level microwave radiation
  • This radiation comes from all directions
  • CBR is associated with cool temperature (2.735 K)
  • The steady state theory does not explain CBR
slide97

Cosmic Background Radiation (CBR)

  • This has been mapped by satellites.
slide99

Big Bang Model

  • Momentum carries material outward while pulls inward
slide100

Big Bang Model

  • Momentum carries material outward while gravity pulls inward
slide101

Big Bang Model

  • Momentum carries material outward while gravity pulls inward
  • The rate of expansion is slowing
slide102

Big Bang Model

  • Momentum carries material outward while gravity pulls inward
  • The rate of expansion is slowing
  • Possible Outcomes
slide103

Big Bang Model

  • Momentum carries material outward while gravity pulls inward
  • The rate of expansion is slowing
  • Possible Outcomes
  • Open Universe –

Expansion of Universe never stops

slide104

Big Bang Model

  • Momentum carries material outward while gravity pulls inward
  • The rate of expansion is slowing
  • Possible Outcomes
  • Open Universe –
  • Closed Universe –

Expansion stops and becomes a contraction

slide105

Big Bang Model

  • Momentum carries material outward while gravity pulls inward
  • The rate of expansion is slowing
  • Possible Outcomes
  • Open Universe –
  • Closed Universe –
  • Flat Universe –

Expansion slows to halt in infinite amt. of time

slide107

Big Bang Model

  • Critical Density
  • The outcome of the Universe depends on the amount (density) of material in it.
slide108

Big Bang Model

  • Critical Density
  • The outcome of the Universe depends on the amount (density) of material in it.
  • Less than critical density (10-26 kg/m3) results in open Universe.
slide109

Big Bang Model

  • Critical Density
  • The outcome of the Universe depends on the amount (density) of material in it.
  • Less than critical density (10-26 kg/m3) results in open Universe.
  • More than critical density means closed Universe
slide110

Big Bang Model

  • Critical Density
  • The outcome of the Universe depends on the amount (density) of material in it.
  • Less than critical density (10-26 kg/m3) results in open Universe.
  • More than critical density means closed Universe
  • Equal to Critical density means flat Universe
slide111

Big Bang Model

  • Critical Density
  • The outcome of the Universe depends on the amount (density) of material in it.
  • Observations show less than critical density, (but there is dark matter)
slide113

Decrease of Rate of Expansion

  • This could be used to tell the outcome of the Universe
slide114

Decrease of Rate of Expansion

  • This could be used to tell the outcome of the Universe
  • Universe’s expansion should be getting slower
slide115

Decrease of Rate of Expansion

  • This could be used to tell the outcome of the Universe
  • Universe’s expansion should be getting slower
  • We observed it’s actually expanding faster
slide116

Inflationary Universe

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

slide117

Calculating Age

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

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

1 pc = 3.1 x 1013 km

‘mega’ (M) = 1 000 000 units