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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.


  • Distances to clusters determined using variable stars.


  • Distances to clusters determined using variable stars.


Variable Stars

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


  • Distances to clusters determined using variable stars.

  • RR Lyrae variables

Brightness pulsates between 1.5 hours and 1 day


  • Distances to clusters determined using variable stars.

  • RR Lyrae variables

  • Cepheid variables

(graph this)

Brightness pulsates between 1 and 100 days


  • 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)


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.



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


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

  • Center has high density of stars


  • 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


  • The MW is a flattened disk shape


  • The MW is a flattened disk shape

  • Galactic center (nucleus) surrounded by nuclear bulge


  • The MW is a flattened disk shape

  • Galactic center (nucleus) surrounded by nuclear bulge

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


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



  • Might be found by measuring luminosity

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


  • Might be found by measuring luminosity

  • Mass is usually found by using our orbital speed


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


  • 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.


  • 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.


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


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


  • 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



  • Young stars form in the arms of the MW


  • Young stars form in the arms of the MW

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



  • MW was originally round.

Notice the arrangement of the oldest stars.


  • 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



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


  • 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.



  • Spiral

M74 in pisces

“Cosmic Frisbee”


  • Spiral

  • Normal spirals (S)


  • Spiral

  • Normal spirals (S)

  • Barred spirals (SB)

NGC 1300 – in Eridanus


  • 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.


  • Spiral

  • Ellipticals

“Cosmic Football”


  • Spiral

  • Ellipticals

  • Divided from E0 to E7.


  • Spiral

  • Ellipticals

  • Divided from E0 to E7.

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


  • Spiral

  • Ellipticals

  • Irregular Galaxies (Irr)

http://www.nasa.gov


  • Masses


  • Masses

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


  • Masses

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

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


  • 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.



  • Local group

M33 -

member of the local group


  • Local group

  • Includes Milky Way

http://www.spacetoday.org


  • Local group

  • Includes Milky Way

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

http://www.via.ee


  • Local group

  • Includes Milky Way

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

  • It’s about 2 million ly across


  • Local group

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

http://www.randybrewer.net


  • 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



  • Discovered by Hubble in 1929


  • Discovered by Hubble in 1929

  • “Red shift”

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



  • Discovered by Hubble in 1929

  • “Red shift”

  • Indicates galaxy is moving away from us


  • 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


  • 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)


  • Discovered by Hubble in 1929

  • “Red shift”

  • Hubble’s law

v = Hd


  • Discovered by Hubble in 1929

  • “Red shift”

  • Hubble’s law

v = Hd

Distance (Mpc)

velocity (km/s)

Hubble’s constant



  • Radio Galaxies


  • Radio Galaxies

  • Two lobes connected by jets of hot gas.

NGC 5128 -

Radio galaxy


  • 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


  • Active Galactic Nuclei (AGN)


  • Active Galactic Nuclei (AGN)

  • Highly energetic galactic cores


  • Active Galactic Nuclei (AGN)

  • Highly energetic galactic cores

  • Output of energy varies



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


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

  • Create emission lines, instead of absorption lines.

Absorption spectrum

Emission spectrum


  • 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).



  • We study stars/galaxies as they were.


  • 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



  • Steady State Theory


  • Steady State Theory

  • The Universe does not change with time.


  • Steady State Theory

  • The Universe does not change with time.

  • The Universe had no beginning


  • Steady State Theory

  • The Universe does not change with time.

  • The Universe had no beginning

  • The Density stays constant


  • 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


  • Big Bang Theory


  • Big Bang Theory

  • All matter began at a point initially


  • Big Bang Theory

  • All matter began at a point initially

  • The matter and space of our Universe has been expanding ever since



  • Low-level microwave radiation


  • Low-level microwave radiation

  • This radiation comes from all directions


  • Low-level microwave radiation

  • This radiation comes from all directions

  • CBR is associated with cool temperature (2.735 K)


  • 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


  • This has been mapped by satellites.



  • Momentum carries material outward while pulls inward


  • Momentum carries material outward while gravity pulls inward


  • Momentum carries material outward while gravity pulls inward

  • The rate of expansion is slowing


  • Momentum carries material outward while gravity pulls inward

  • The rate of expansion is slowing

  • Possible Outcomes


  • Momentum carries material outward while gravity pulls inward

  • The rate of expansion is slowing

  • Possible Outcomes

  • Open Universe –

Expansion of Universe never stops


  • 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


  • 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


  • Critical Density

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


  • 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.


  • 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


  • 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


  • 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)



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


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

  • Universe’s expansion should be getting slower


  • 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


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


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



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