Stars Final
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| When was "Space-Time" born | 13.8 billion years ago via the Big Bang.
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| What determines the shape/fate of the Universe? | The amount of mass (normal vs dark) it contains. and dark energy.
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| Galaxy | A large collection of stars and gas.
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| How many stars in a galaxy like the Milky Way? | >100 billion.
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| How many galaxies in the universe? | hundreds of billions
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| How far away is the center of the Milky was from the sun? | 27,000 light years
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| How did the Milky Way form? | Probably from the merger of many smaller protogalaxies. (Fun Fact! Several protogalaxies are orbiting the milky way as satellite galaxies.
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| Are galaxies distributed uniformly? | No. They are found in groups or clusters.
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| The Local Group. | Where the Milky Way is located.
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| Where is the Local Group located? | on the outskirts of the Virgo cluster.
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| What dominates the composition of the Coma cluster? | elliptical and S0 galazies.
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| superclusters | when clusters and groups bunch together they form superclusters.
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| Redshift Surveys | Reveal the distribution of clusters and superclusters.
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| hierarchical clustering | small objects formed first and then grouped together.
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| Structure formation models | Can simulate the formation of galaxies, but will need, the amount of dark matter/energy, the size of original density variations, and a "complete list of all ingredients." very difficult to do.
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| Why is dark matter necessary for this theory/models | Gravity cannot grow galaxies with just the contribution of normal matter. "Dark matter provides the seeds!" and must be >30x more abundant
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| Galaxy formation process | At recombination, dark matter clumps exist. Gravity will eventually begin slowing the expansion of a dark matter clump so that it eventually will reach it's maximum size. Normal matter begins to fall into the clump.
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| Galaxy formation process cont. | Dark/normal matter begin to collapse until the dark matter can collapse no further. Normal matter will continue to collapse, first into smaller clumps, and then into a spiral galaxy
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| Distribution of a young universe | The young universe was very uniform, until dark matter clumps began to expand more slowly than the universe as a whole. They eventually collapsed to draw in normal matter.
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| How to find dark matter | Dark matter reveals itself through gravitational effects. For example, for gravity to hold the hot x-ray emitting gas, it must be more massive than we perceive. Galaxy clusters are mostly dark matter.
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| Gravitation lensing | Creates bright arcs of deflected light. The greater the deflection, the greater the mass. Reveals dark matter
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| Mergers | when galaxies/clusters collide to become new galaxies/clusters.
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| The Millennium Run | N-body supercomputer simulation. >10billion particles, each containing ~1 billion solar masses of dark matter. Starts 379,000 years after the universe began. In a cube 8 billion light years^3
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| How to characterize dark matter | its average speed, and its composition.
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| Cold dark matter | slow-ish (compared to the speed of light). Forms galaxies.
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| Hot dark matter | moves rapidly - likely a result of neutrinos from the Big Bang.
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| Galaxy formation as compared with star formation. | Very similar: gravitation instability, fragmentation, compression, heating, and thermal support, angular momentum and formation of disks. End product is a centrally concentrated material with surrounding disk.
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| Can elliptical galaxies be made from mergers of spiral galaxies? | yes.
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| Evolution of galaxies | Galaxies form early, structures, voids, and filaments form later on.
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| Models vs. observations | Models tell us where the mass is, but observations tell us where the light is.
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| Redshift surveys | reveal the distribution of clusters and superclusters.
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| Homogeneous Universe | Average properties of one sufficiently large box are the same as another box.
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| Isotropic Universe | Average properties of the universe look the same in all directions
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| Critical density | The faster the universe is expanding, the harder it is to stop it. The more mass there is, the more gravity there is to halt the expansion. Critical density is the density neede dot slow the universe to a stop, but not to reverse it.
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| Gamma(mass) | Gamma(mass)=Actual density of a universe/Critical density of the universe. = 1 means critical density. if gamma>1universe will contract. Gamma<1, expansion will go on forever, may slow a little.
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| The Big Cruch | When Gamma(mass)>1. The universe will contract
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| Actual Gamma Value | with ordinary stars/galaxies, gamma=0.02.
dark matter in and between galaxies, gamma=0.3
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| Is expansion slowing down or speeding up? | speeding up (discovery made in the 1990s). There exists an energy that pushes space acting against gravity.
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| The Cosmological Constant | gamma(a)- a force that is not understood that is causing the expansion of the universe to speed up. "dark energy". Makes it more difficult for gravity to reverse the expansion.
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| The two numbers that characterizes the universe | gamma(mass), gamma(a).
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| gamma(a) | 0.7
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| The shape of the universe | Three options:
1)flat universe: gamma(mass)+gamma(a)=1
2)Open universe, infinite (saddle like): gamma(mass)+gamma(a)<1.
3)Closed, finite, spherical: gamma(mass)+gamma(a)>1.
THE UNIVERSE IS FLAT.
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| The flatness problem | gamma(mass)+gamma(a)=1. This is a VERY specific value.
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| The horizon problem | The CBR is almost exactly the same temperature in all directions, when they are really too far apart to be able to trasmit such temperature.
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| Cosmic Inflation | In it's expansion, the universe became more uniform.
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| Four fundamental forces of nature | strong nuclear, electromagnetic, weak nuclear, and gravitational.
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| The electroweak theory | QED(electromagnetic force)and the weak force are combine in the electroweak theory
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| Standard model of physics | electroweak+strong(QCD)
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| Grand unification theory | GUT=strong force+electroweak force. predicts proton decay. GUT+gravity=theory of everything (TOE)
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