front 1 What kind of galaxy do we live in? | back 1 We live in a DISK galaxy, not an elliptical or irregular galaxy
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front 2 Panoramic views of the Milky Way in different bands of the spectrum | back 2 ![]() We can observe the star-gas-star cycle through these different wavelengths of light |
front 3 What is the interstellar gas medium composed of? | back 3 It is composed of dust and gas --> It obscures out view because it absorbs visible light |
front 4 We see our galaxy EDGE - ON.
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front 5 If we could view the Milky Way from above the disk (face-on), we would be able to see its spiral arms | back 5 ![]() |
front 6 How do stars orbit in our galaxy? | back 6 -Stars in the disk all orbit in the direction, but will a little up-and-down motion
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front 7 Why do orbits of bulge stars bob up and down? | back 7 The gravity of all stuff in the disk pulls them toward the midplane |
front 8 Orbits of stars in the bilge and halo have random orientations | back 8 ![]() |
front 9 What is the ORBITAL VELOCITY LAW and what does it tell us? | back 9 - M = (r x v^2) / G
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front 10 How can we use the Sun's orbital motion (radius and velocity) to tell us the mass withing the Sun's orbit? | back 10 Sun's velocity: 220 km/s = 2.2 x 10^5 m/s
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front 11 What does our galaxy look like? | back 11 Our galaxy consists of a disk of stars and gas, with a bulge of stars at the center of the disk, surrounded by a large spherical halo |
front 12 How is gas recycled in our galaxy? | back 12 ![]() Through the star-gas-star cycle (It recycles gas from old stars into new star systems)
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front 13 How does gravity affect the star-gas-star cycle? | back 13 Gravity forms stars out of gas in molecular clouds, completing the star-gas-star cycle |
front 14 What are the characteristics of high-mass stars? | back 14 They have strong stellar winds that blow bubbles of hot gas into the interstellar medium |
front 15 What are the characteristics of low-mass stars? | back 15 They return gas to interstellar space through stellar winds and planetary nebulae |
front 16 What is the effect of X-rays in elements? | back 16 X-rays from hot gas in supernova remnants reveal newly made heavy elements |
front 17 Galactic fountains | back 17 - Multiple supernovae create huge hot bubbles that can blow out of the disk
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front 18 Summary of galactic recycling | back 18 - Stars make new elements by fusion
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front 19 Where are ionization nebulae found and why are they important? | back 19 - Ionization (red) nebulae are found living around short-lived high-mass stars, signifying active star formation |
front 20 What is the purpose of the reflection nebulae? | back 20 Reflection nebulae scatters the light from stars |
front 21 Why are reflection nebulae blue? | back 21 Blue light is scattered more than red light |
front 22 Where is much of the star formation in the disk occur? | back 22 In the spiral arms because the gas clouds are compressed in the arms. |
front 23 Are spiral arms wound material? | back 23 ![]() No! They are density waves!
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front 24 Where do stars tend to form in our galaxy? | back 24 Active star-forming regions contain molecular clouds, hot stars, and ionization nebulae
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front 25 Halo stars | back 25 - 0.02 - 0.2% of heavy elements (O, Fe, etc.)
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front 26 Disk Stars | back 26 - 2% heavy elements
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front 27 How did our galaxy form? | back 27 Our galaxy formed form a cloud of intergalactic gas
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front 28 Where will galactic gas be in a trillion years? | back 28 Locked into white dwarfs and low- mass stars |
front 29 Spirals suffer minor mergers, Elliptical suffers a few major mergers | back 29 ![]() |
front 30 What clues does out galaxy's history do halo stars hold? | back 30 Halo stars are all old, with a smaller proportion of heavy elements than disk stars, indicating that the halo formed first |
front 31 How did our galaxy form | back 31 Halo stars formed early in the galaxy's history; disk stars form later, after much of the galaxy's gas settled into a spinning disk |
front 32 What lies in the center of our galaxy? | back 32 - ORBITS OF STARS NEAR THE CENTER OF OUR GALAXY INDICATE THAT IT CONTAINS A BLACK HOLE WITH A MASS 4 MILLION TIMES THE MASS OF THE SUN
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front 33 Stars appear to orbit something massive and invisible, what can it be? | back 33 Black hole |
front 34 Orbits of stars indicate a mass of: | back 34 About 4 million MSun |
front 35 Can we use Kepler's 3rd Law to find the mass? | back 35 Yes! Stars orbit far from the black hole, so it's just like any other mass |
front 36 what do X-ray flares from galactic center suggest? | back 36 That tidal forces of suspected black hole occasionally tear apart chunks of matter about to fall in |
front 37 Hubble Deep Field | back 37 Our deepest images of the universe show a great variety of galaxies, some of them billions of light-years away - and thus young |
front 38 Galaxies and Cosmology | back 38 - A galaxy's age, its distance and the age of the universe are all closely related
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front 39 What are the three types of galaxies? | back 39 Spiral, Elliptical, and Irregular |
front 40 Spiral galaxy | back 40 Disk component: Has stars of all ages, and it has much gas and dust
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front 41 Why does ongoing star formation lead to a blue-white appearance? | back 41 Short-lived blue stars outshine the others |
front 42 Barred spiral galaxy | back 42 ![]() Has a bar of stars across the bulge |
front 43 Lenticular galaxy | back 43 ![]() Has a disk like a spiral galaxy, but it is much less dusty/ gas (intermediate b/w spiral and elliptical) |
front 44 Elliptical galaxy | back 44 ![]() All spheriodal component, virtually no disk component
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front 45 Irregular galaxy | back 45 ![]() Blue-white color indicates ongoing star formation |
front 46 Hubble's galaxy classes | back 46 ![]() The rounder the appearance, the spheroid component dominates; the higher the spiral arms, the disk component domincates |
front 47 Peculiar Galaxies | back 47 ![]() |
front 48 Interacting Galaxies | back 48 ![]() |
front 49 How are galaxies grouped together? | back 49 - Spiral galaxies are often found in groups of galaxies (up to a few dozen galaxies, and they are also found on the outskirts of clusters)
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front 50 What is the motion of galaxies in a group or cluster? | back 50 Any galaxy orbits under the pull of all the other galaxies |
front 51 How do we measure the distances to galaxies? | back 51 Step 1: Determine the size of the solar system using radar
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front 52 Inverse-Square Law | back 52 The relationship between apparent brightness and luminosity depends on distance
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front 53 Standard candles | back 53 A standard candle is something whose luminosity we know without having to measure its distance
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front 54 Cepheids | back 54 ![]() - Star pulsates so brightness changes
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front 55 Why are Cepheid stars great fro measuring the distance to very far away galaxies? | back 55 Because they are very luminous, they can be seen at great distance |
front 56 The Puzzle of "Spiral Nebulae" | back 56 Before Hubble, some scientist argued that "spiral nebulae" were entire galaxies like our milky way, while others believed they were smaller collections of stars within the Milky Way
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front 57 The Hubble Law | back 57 ![]() The spectral features of virtually all galaxies are redshifted, which means that they are all moving away from us and move away faster the further they are
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front 58 Your friend leaves your house. She later calls you on her cell phone, saying that she took a while to get up to speed, but then drove at 60 miles an hour directly away from you and is now 60 miles away. How long has she been gone? | back 58 More than 60 minutes |
front 59 Age of the universe | back 59 - Hubble's constant tells us the age of universe because it relates the velocities and distances of all galaxies --> Age = Distance/ Velocity
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front 60 Is Ann Arbor the center of the universe? How can we understand that we appear to be at the center of an expansion? It seems to violate the Copernican Principle | back 60 -No! Space itself expands
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front 61 Cosmological principle | back 61 - The universe looks about the same no matter where you are within it
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front 62 The horizon | back 62 Distances between faraway galaxies change while light ravels
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front 63 The cosmological horizon marks the limits of the OBSERVABLE universe | back 63 Galaxies that were close in the early universe have been separating for its entire history and are now the most distant objects we can see: ~ 47 billion years
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front 64 How do the distance between measurements tell is the age of the universe? | back 64 - Measuring a galaxy's distance and speed allows us to figure out how long the galaxy took to reach its current distance.
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front 65 How does the universe's expansion affect our distance measurements? | back 65 We specify the present location of objects; they were closer when light set out. |
front 66 Why do galaxies differ? | back 66 ![]() The gas density of a galaxy's protogalactic clouds may determine whether it ends up spiral or elliptical; The spin will determine size of disk |
front 67 Conditions in a protogalactic cloud: Density | back 67 Elliptical galaxies could come from dense protogalactic clouds that were able to cool and form stars before gas settled into a disk |
front 68 Conditions in a protogalactic cloud: Spin | back 68 The initial angular momentum of the protogalactic cloud could determine the size of the resulting disk |
front 69 Distant Red Ellipticals | back 69 Observations of some distant red elliptical galaxies support the idea that most of their stars formed very early in the history of the universe --> That suggests that we should also consider the effects of collisions |
front 70 Collisions in galaxies | back 70 ![]() - collisions were much more likely early in time because galaxies were closer together
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front 71 How are quasars powered? | back 71 - If the center of a galaxy is unusually bright, we call it an ACTIVE GALACTIC NUCLEUS (Quasars are the most luminous examples)
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front 72 What can you conclude from the fact that quasars usually have very large redshifts? | back 72 They are generally very distant, they were more common early in time, galaxy collisions might turn them on, and nearby galaxies might hold dead quasars |
front 73 Quasars powerfully radiate energy over a wide range of wavelengths, indicating that they contain matter with a wide range of temperatures | back 73 ![]() |
front 74 Radio Galaxies | back 74 ![]() They contain active nuclei shooting vast jets of plasma that emits radio waves coming from electrons that move at near light speed
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front 75 Characteristics of Active Galaxies | back 75 - Their luminosity can be enormous (>10^12 LSun)
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front 76 How can you explain all the properties of quasars? | back 76 By the accretion of gas onto a super massive black hole |
front 77 Energy from a black hole | back 77 - Gravitational potential energy of matter falling into a black hole turns into kinetic energy
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front 78 What do we think comes from twisting the magnetic field in the inner part of accretion disk | back 78 ![]() Jetsg |
front 79 The active galactic nuclei zoo | back 79 ![]() |
front 80 Do super massive black holss really exist? | back 80 ![]() Orbits of stars at center of Milky Way galaxy indicate a black hole with mass of 4 million MSun
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front 81 What is the size of the super massive black hole in M87, relative to our Solar System? | back 81 A little bigger than Pluto's orbit |
front 82 Black holes in galaxies | back 82 Many nearby galaxies (perhaps all of them) have super massive black holes at their centers.
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front 83 Galaxies and Black holes | back 83 ![]() The mass of a galaxy's central black hole is closely related to the mass of its bulge.
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front 84 How do quasars let us study gas between the galaxies? | back 84 ![]() - Gas clouds between a quasar and Earth absorb some of the quasar's light
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front 85 How are quasars powered? | back 85 - Active galactic nuclei are very bright objects seen in the centers of some galaxies, and quasars are the most luminous type
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front 86 What key features of the universe are explained by inflation? | back 86 - The origin of the structure, the smoothness of the universe on large scales, the nearly critical density of the universe
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front 87 the geometry of the universe is closely related to ... | back 87 total density of matter and energy (density = critical [flat]) |
front 88 Origin of inflation | back 88 Inflation can make all the structure by stretching tiny quantum ripples to enormous size. These ripples in density then become seeds for all structures in the universe |
front 89 What is the horizon problem? | back 89 Despite the distance between objects, microwave temperature can be nearly identical on opposite sides of the sky because they were close together but inflation pushed them further apart |
front 90 What is the flatness problem? | back 90 Inflation of the universe flattens its overall geometry like the inflation of a balloon, causing the overall density of matter plus energy to the very close to the critical density |
front 91 Did inflation really occur? | back 91 ![]() We can compare the structures we see in detailed observations of the microwave background with predictions for the "seeds" that should have been planted by inflation. So far, our observations of the universe agree well with models in which inflation planted "seeds." |
front 92 What do we infer from the CMB? | back 92 - The overall geometry is flat [ Total mass + energy has critical density]
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front 93 Why is it dark at night? | back 93 Because the universe has finite age |
front 94 Why is the darkness of the night sky evidence for the Big Bang? | back 94 The night sky is dark because the universe changes with time. As we look out in space, we can back to time when there were no stars. |
front 95 What is Olbers' Paradox? | back 95 If the universe was INFINITE, UNCHANGING, AND EVERYWHERE THE SAME, them stars would cover the night sky |
front 96 What is dark matter? | back 96 An undetected form of mass that emits little or no light, but whose existence we infer from its gravitational influence. |
front 97 what is dark energy? | back 97 An unknown form of energy that seems to be the source of a repulsive force causing the expansion of the universe to accelerate |
front 98 What is the contents of the universe? | back 98 - Ordinary matter: ~4.4%
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front 99 What is the evidence for dark matter in galaxies? | back 99 We measure the mass of the solar system using the orbital period and and average distance of orbital planets. We would predict that velocity falls as square root of distance.
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front 100 What is the rotation curve? | back 100 A plot of orbital velocity versus orbital radius. The solar system's rotation curve declines because the Sun has almost all the mass
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front 101 How can we measure the rotation curves of other spiral galaxies? | back 101 By using the Doppler shift of the 21 cm line of atomic hydrogen.
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front 102 What would you conclude about a galaxy whose rotational velocity rises steadily with distance beyond the visible part of its disk? | back 102 It is specially rich in dark matter |
front 103 What is the evidence for dark matter in clusters of galaxies? | back 103 We can measure the velocities of galaxies in a cluster form from their Doppler shifts.
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front 104 What is gravitational lensing? | back 104 It is the bending of light rays by gravity. They can tell us a cluster's mass. |
front 105 Clusters: Final count | back 105 All three methods of measuring cluster mass indicate similar amounts of dark matter in galaxy clusters (85% dark matter, 13% hot gas, 2% stars) |
front 106 Cosmic flows | back 106 ![]() We find similar proportions of dark to regular matter here: regular matter is only 15% the whole, and stars a few percent |
front 107 Does dark matter really exist? | back 107 Dark matter really exists, and we are observing the effects of its gravitational attraction. |
front 108 What is dark matter? | back 108 ![]() Particle dark matter: Weakly interacting massive particles
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front 109 Why believe in WIMPs? | back 109 There is not enough ordinary matter. Physics suggests the existence of "supersymmetric particles." These could be left over from Big Bang. Models involving such particles explain how galaxy formation works. |
front 110 What is the role of dark matter in the formation of our galaxy? | back 110 Dark matter doesn't interact with radiation, therfore local over densitties of dark matter could start to collapse early: ~1,000 years after Big Bang.
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front 111 Baryon radiation Interaction | back 111 no data |
front 112 Why do stars and globular clusters in the halo of our galaxy not collapse to form a bulge or disk? | back 112 They have no way to lose orbital energy |
front 113 What is the role of radiation? | back 113 Once a dark matter "halo" has formed, dark matter can't sink further because it can't radiate away its orbital energy, but the baryons can.
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front 114 What are the largest structures in the universe? | back 114 [Galaxies appear to be distributed in gigantic chains and sheets that surround great voids.]
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front 115 Why is accelerating expansion evidence for dark energy? | back 115 ![]() - The fate of the universe depends on the amount of dark matter. Since the amount of dark matter is about 25% of the critical density, we expect the expansion of the universe to overcome its gravitational pull. In fact, expansion speeds up (V)
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front 116 Supppose that the universe has more dark matter than we think there is today. How would this change the age we estimate from the expansion rate? | back 116 The estimated age would be smaller |
front 117 White dwarf supernovae | back 117 ![]() The brightness of distance white dwarf supernovae lets us extend the Hubble diagram to great distance. An accelerating universe best fits the supernova data. |
front 118 Why is flat geometry evidence for dark energy? | back 118 ![]() Measurements of the cosmic microwave background indicate that the universe has a flat geometry, thus dark energy is needed to fill out the remaining mass-energy |
front 119 What is the fate of the universe? | back 119 The eventual fate of the universe depends upon the rate of the acceleration of the expansion. If the universe does not end in a Big Rip, it should keep expanding for a very long time. All matter will eventually end up as part of black holes, which will eventually evaporate. |
front 120 What have we learned? | back 120 In the absence of the repulsive force of dark energy, the expansion of the universe will not be accelerating. Also, evidence from the CMB indicates that the universe is very near critical density, requiring an additional contribution to the mass-energy of the universe. Lastly, the universe should keep expanding indefinitely, eventually consisting of a dilute sea of fundamental particles. |