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Galaxies and the Universe Chap. 31 The Milky Way 31.1 Other Galaxies in the Universe 31.2 Cosmology 31.3 The Milky Way Objectives • determine the size and shape of the Milky Way, as well as Earth’s location within it. • describe how the Milky Way formed. I. Discovering the Milky Way A. Distances to clusters determined using variable stars. I. Discovering the Milky Way A. Distances to clusters determined using variable stars. Variable Stars Stars in the ‘giant’ branch of HR diagram that pulsate in brightness I. Discovering the Milky Way A. Distances to clusters determined using variable stars. 1. RR Lyrae variables Brightness pulsates between 1.5 hours and 1 day I. Discovering the Milky Way A. Distances to clusters determined using variable stars. 1. RR Lyrae variables 2. Cepheid variables Brightness pulsates between 1 and 100 days (graph this) I. Discovering the Milky Way A. Distances to clusters determined using variable stars. 1. RR Lyrae variables 2. Cepheid variables 3. 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. II. Locating the Center of the Galaxy II. Locating the Center of the Galaxy A. Globular clusters are centered around a point about 28,000 ly away II. Locating the Center of the Galaxy A. Globular clusters are centered around a point about 28,000 ly away B. Center has high density of stars II. Locating the Center of the Galaxy A. Globular clusters are centered around a point about 28,000 ly away B. Center has high density of stars C. Center is toward Sagittarius constellation http://www.esa.int III. Shape of Milky Way A. The MW is a flattened disk shape III. Shape of Milky Way A. The MW is a flattened disk shape B. Galactic center (nucleus) surrounded by nuclear bulge III. Shape of Milky Way A. The MW is a flattened disk shape B. Galactic center (nucleus) surrounded by nuclear bulge C. A spherical-shaped halo containing older stars surrounds the disk. III. Shape of Milky Way D. Four major spiral arms (and several minor spiral arms) have been identified IV. Mass of the Milky Way IV. Mass of the Milky Way A. Might be found by measuring luminosity Remember that luminosity is related to mass. Stars that are bigger are also _________. IV. Mass of the Milky Way A. Might be found by measuring luminosity B. 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 IV. Mass of the Milky Way A. Might be found by measuring luminosity B. Mass is usually found by using our orbital speed C. Since the MW is about 100 billion times the mass of the Sun, an average sized star, the MW must contain about stars. IV. Mass of the Milky Way A. Might be found by measuring luminosity B. Mass is usually found by using our orbital speed C. 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. V. Mass of the Center of the Milky Way A. Stars near the center orbit center very fast – this indicates a very center V. Mass of the Center of the Milky Way A. Stars near the center orbit center very fast – this indicates a very massive center V. Mass of the Center of the Milky Way A. Stars near the center orbit center very fast – this indicates a very massive center B. 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 VI. Age of Stars in Milky Way VI. Age of Stars in Milky Way A. Young stars form in the arms of the MW VI. Age of Stars in Milky Way A. Young stars form in the arms of the MW B. Old stars are found in the halo/nuclear bulge. VII. Formation of Milky Way VII. Formation of Milky Way A. MW was originally round. Notice the arrangement of the oldest stars. VII. Formation of Milky Way A. MW was originally round. B. The MW cloud collapsed and flattened into a disk shape. The End Other Galaxies – 30.2 Objectives • Describe how astronomers classify galaxies • Identify how galaxies are organized into clusters and superclusters • Describe the expansion of the universe I. Identifying I. Identifying A. Astronomers saw other galaxies before they knew what they were. I. Identifying A. Astronomers saw other galaxies before they knew what they were. B. Edwin Hubble measured their distances to confirm they were not in MW. He used variable stars to do it. II. Classifying II. Classifying A. Spiral M74 in pisces “Cosmic Frisbee” II. Classifying A. Spiral 1. Normal spirals (S) II. Classifying A. Spiral 1. Normal spirals (S) 2. Barred spirals (SB) NGC 1300 – in Eridanus II. Classifying A. Spiral 1. Normal spirals (S) 2. Barred spirals (SB) 3. These are further divided by how tightly wound arms are (a, b, c) Type a represents tightly wound arm with bright nucleus. II. Classifying A. Spiral B. Ellipticals “Cosmic Football” II. Classifying A. Spiral B. Ellipticals 1. Divided from E0 to E7. II. Classifying A. Spiral B. Ellipticals 1. Divided from E0 to E7. 2. E7 has a large ratio of major axis/minor axis, E0 is circular. II. Classifying A. Spiral B. Ellipticals C. Irregular Galaxies (Irr) http://www.nasa.gov II. Classifying D. Masses II. Classifying D. Masses 1. Dwarf ellipticals have few stars (about 1 million). II. Classifying D. Masses 1. Dwarf ellipticals have few stars (about 1 million). 2. Large spirals, like MW, have about 100 million stars. II. Classifying D. Masses 1. Dwarf ellipticals have few stars (about 1 million). 2. Large spirals, like MW, have about 100 million stars. 3. Giant ellipticals have mass of 100 trillion x the sun. III. Groups & Clusters III. Groups & Clusters A. Local group M33 member of the local group III. Groups & Clusters A. Local group 1. Includes Milky Way http://www.spacetoday.org III. Groups & Clusters A. Local group 1. Includes Milky Way 2. About 35 known members including Andromeda and several dwarf galaxies. http://www.via.ee III. Groups & Clusters A. Local group 1. Includes Milky Way 2. About 35 known members including Andromeda and several dwarf galaxies. 3. It’s about 2 million ly across III. Groups & Clusters A. Local group B. There are clusters much bigger than local group (ex. Virgo) http://www.randybrewer.net III. Groups & Clusters A. Local group B. There are clusters much bigger than local group (ex. Virgo) C. Mass of clusters are bigger than the sum of the parts. This is evidence for existence of dark matter IV. The Expanding Universe IV. The Expanding Universe A. Discovered by Hubble in 1929 IV. The Expanding Universe A. Discovered by Hubble in 1929 B. “Red shift” Light waves are stretched out due to relative motion of source and observer away from each other. Red Shift IV. The Expanding Universe A. Discovered by Hubble in 1929 B. “Red shift” 1. Indicates galaxy is moving away from us IV. The Expanding Universe A. Discovered by Hubble in 1929 B. “Red shift” 1. Indicates galaxy is moving away from us 2. Hubble determined the degree of red shift depends on the distance away IV. The Expanding Universe A. Discovered by Hubble in 1929 B. “Red shift” 1. Indicates galaxy is moving away from us 2. Hubble determined the degree of red shift depends on the distance away 3. All galaxies are moving away from all other galaxies (not just Earth) IV. The Expanding Universe A. Discovered by Hubble in 1929 B. “Red shift” C. Hubble’s law v = Hd IV. The Expanding Universe A. Discovered by Hubble in 1929 B. “Red shift” C. Hubble’s law v = Hd velocity (km/s) Distance (Mpc) Hubble’s constant V. Active Galaxies V. Active Galaxies A. Radio Galaxies V. Active Galaxies A. Radio Galaxies 1. Two lobes connected by jets of hot gas. NGC 5128 Radio galaxy V. Active Galaxies A. Radio Galaxies 1. Two lobes connected by jets of hot gas. 2. Observed by radio telescopes because they emit more radio waves than visible light. Radio telescope V. Active Galaxies B. Active Galactic Nuclei (AGN) V. Active Galaxies B. Active Galactic Nuclei (AGN) 1. Highly energetic galactic cores V. Active Galaxies B. Active Galactic Nuclei (AGN) 1. Highly energetic galactic cores 2. Output of energy varies VI. Quasars VI. Quasars A. Like other galaxies, but these are strong radio emitters. VI. Quasars A. Like other galaxies, but these are strong radio emitters. B. Create emission lines, instead of absorption lines. Absorption spectrum Emission spectrum VI. Quasars A. Like other galaxies, but these are strong radio emitters. B. Create emission lines, instead of absorption lines. C. These objects have a very large red shift (so they are very far away). VII. Looking back in time VII. Looking back in time A. We study stars/galaxies as they were. VII. Looking back in time A. We study stars/galaxies as they were. B. Seeing quasars that are very far (old) suggests a possible ‘quasar stage’ during universe history. The End Cosmology – 31.3 Objectives • Explain the different theories about the formation of the universe • Describe the possible outcomes of universal expansion I. Models I. Models A. Steady State Theory I. Models A. Steady State Theory 1. The Universe does not change with time. I. Models A. Steady State Theory 1. The Universe does not change with time. 2. The Universe had no beginning I. Models A. Steady State Theory 1. The Universe does not change with time. 2. The Universe had no beginning 3. The Density stays constant I. Models A. Steady State Theory 1. The Universe does not change with time. 2. The Universe had no beginning 3. The Density stays constant 4. As Universe expands, new material is created and added I. Models B. Big Bang Theory I. Models B. Big Bang Theory 1. All matter began at a point initially I. Models B. Big Bang Theory 1. All matter began at a point initially 2. The matter and space of our Universe has been expanding ever since II. Cosmic Background Radiation (CBR) II. Cosmic Background Radiation (CBR) A. Low-level microwave radiation II. Cosmic Background Radiation (CBR) A. Low-level microwave radiation B. This radiation comes from all directions II. Cosmic Background Radiation (CBR) A. Low-level microwave radiation B. This radiation comes from all directions C. CBR is associated with cool temperature (2.735 K) II. Cosmic Background Radiation (CBR) A. Low-level microwave radiation B. This radiation comes from all directions C. CBR is associated with cool temperature (2.735 K) D. The steady state theory does not explain CBR II. Cosmic Background Radiation (CBR) E. This has been mapped by satellites. III. Big Bang Model III. Big Bang Model A. Momentum carries material outward while pulls inward III. Big Bang Model A. Momentum carries material outward while gravity pulls inward III. Big Bang Model A. Momentum carries material outward while gravity pulls inward B. The rate of expansion is slowing III. Big Bang Model A. Momentum carries material outward while gravity pulls inward B. The rate of expansion is slowing C. Possible Outcomes III. Big Bang Model A. Momentum carries material outward while gravity pulls inward B. The rate of expansion is slowing C. Possible Outcomes 1. Open Universe – Expansion of Universe never stops III. Big Bang Model A. Momentum carries material outward while gravity pulls inward B. The rate of expansion is slowing C. Possible Outcomes 1. Open Universe – 2. Closed Universe – Expansion stops and becomes a contraction III. Big Bang Model A. Momentum carries material outward while gravity pulls inward B. The rate of expansion is slowing C. Possible Outcomes 1. Open Universe – 2. Closed Universe – 3. Flat Universe – Expansion slows to halt in infinite amt. of time III. Big Bang Model D. Critical Density 1. The outcome of the Universe depends on the amount (density) of material in it. III. Big Bang Model D. Critical Density 1. The outcome of the Universe depends on the amount (density) of material in it. a) Less than critical density (10-26 kg/m3) results in open Universe. III. Big Bang Model D. Critical Density 1. The outcome of the Universe depends on the amount (density) of material in it. a) Less than critical density (10-26 kg/m3) results in open Universe. b) More than critical density means closed Universe III. Big Bang Model D. Critical Density 1. The outcome of the Universe depends on the amount (density) of material in it. a) Less than critical density (10-26 kg/m3) results in open Universe. b) More than critical density means closed Universe c) Equal to Critical density means flat Universe III. Big Bang Model D. Critical Density 1. The outcome of the Universe depends on the amount (density) of material in it. d) Observations show less than critical density, (but there is dark matter) IV. Decrease of Rate of Expansion IV. Decrease of Rate of Expansion A. This could be used to tell the outcome of the Universe IV. Decrease of Rate of Expansion A. This could be used to tell the outcome of the Universe B. Universe’s expansion should be getting slower IV. Decrease of Rate of Expansion A. This could be used to tell the outcome of the Universe B. Universe’s expansion should be getting slower C. We observed it’s actually expanding faster IV. Inflationary Universe 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 The End