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71 Cards in this Set
- Front
- Back
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Extincion of Light from the Milky Way Galaxy
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Dust obscures visible light from stars in the disk of the galaxy and obstructs our view
Accomplishes this by absorbing and scattering photons *NOTE: The longer the wavelength, the farther it can make it through the disk of the galaxy and not be absorbed or scattered |
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Diagram of a Galaxy
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Consists of a Disk with a Black Hole (Nucleus) at the center, surrounded by the Bulge. The Halo faintly surrounds the Bulge and Disk and contains Globular Clusters in an almost spherical arrangement.
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Star Clusters
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Gravitaionally bound group of stars that all formed at the same time and have the same age
Subdivided into Open Clusters and Globular Clusters |
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Open Clusters
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Fewer number of stars, found mostly in the Disk, contain lots of heavy elements, and are old in age
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Globular Clusters
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Larger amount of stars, found mostly in the Halo, contain few heavy elements, and are younger in age
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Fundamental Differences in Galaxies
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Mass
Spin Gas Content Age of Stars Spiral Structures and Bars (Superficial) |
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Elliptical Galaxies
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Smooth, featureless galaxies that are typically round or oblong in shape and contain mostly older stars
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Spiral Galaxies
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Contain a pronounced disk and bulge with spiral arms that facilitate ongoing star formation
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Lenticular Galaxies
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Contains a Disk and a Bulge but does not have spiral arms or ongoing star formation
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Other Galaxy Classifications
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Interacting and Disturbed galaxies, small galaxies, and irregular galaxies
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Differences between Disks and Bulges
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1. Gas Content (cold vs. hot)
2. Age of Stars (young vs. old) 3. Shape (thin vs. round) 4. Motion of Stars (linear vs. circular) |
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Dopplar Shift
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z = (λ - λo) / λo = v / c
Apparent change in wavelength of a radiation because of relative motion between the observer and the source |
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Blueshift
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Motion along the line of sight when the source moves toward the observer (produces a negative dopplar shift)
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Redshift
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Motion along the line of sight when the source moves away from the observer (produces a positive dopplar shift)
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Types of Shifts
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1. Dopplar Shift (due to relative motion toward or away)
2. Cosmological Redshift (due to the expansion of the universe and always results in a redshift) 3. Gravitational Redshift (due to vertical distance in a gravitational field; as light wave goes up its wavelength increases and frequency decreases) |
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Rotational Velocity
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Vrot = c x z
or Vrot = √ (G x M) / r Uses the Dopplar shifts of Hydrogen lines (HI 21 cm lines) in galactic disks to determine how fast they are spinning (an similar concepts) |
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Angular Rotational Speed
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Ω = (2 x π) / p = Vrot / r
Describes the amount of time it takes for an object to complete its orbit at a specified velocity (Vrot) *NOTE: P is period and Omega is the angular speed |
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Rotational Velocity and Angular Speed
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Rotational Velocities increase proportionally as distance increases; however, Angular speed remains constant
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Evidence for Dark Matter
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1. On the level of a single galaxy, observed rotational curves are nearly flat suggesting that there must be extra mass that is not traced by light (not visible because it doesn't produce any radiation) Basically, there is not enough mass in the known stars and gas to account for the high rotational velocities of galaxies.
2. On the scale of galactic clusters, there must be enough mass to hold galaxies in the cluster and keep them from flying away. Because the total mass is about 10 times more than the total mass in stars and gas, something else must be present. |
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What is Dark Matter?
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Two Possibilities:
1. Faint lumps of baryonic matter (brown dwarfs, black holes, planets), called MACHOS (Massice Compact Halo Objects) 2. Exotic subatomic particles, called WIMPS (similar to neutrinos) |
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Distribution of Galaxies
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Galaxies are distributed into Groups, Clusters, and Superclusters
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Galaxies Groups
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Consist of about 10 to 50 galaxies, include mostly spirals and dwarfs, and have no central concentration
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Galaxy Clusters
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Consist of about 1000 galaxies, contain lots of ellipticals and lenticular galaxies, and have a high central concentration of mass
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Galaxy Superclusters
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Filimentary shaped and sheetlike and about 10,000 galaxies in size with clusters and groups found at intersections
Regions between filiments are called voids and have very low densities |
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Gravitational Lensing
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The deflection of the path of light because of the gravitational force of an interceding object (called the lens)
Often produces two or more exact images, enabling us to sometimes determine if gravitational lensing is at work |
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Quasars
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Point sources of light that are very distant and very luminous with very large redshifts due to expansion of the universe, indicating that they formed early in the timeline of the universe
Also, they pulsate in a consistant manner, which tells astronomers that they are rather small in size |
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Active Galactic Nuclei
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Supermassive Black Holes in the centers of large galaxies that consist of an accrection disk, jets, radio lobes, and large outlying ring of gas and dust and which emit huge amounts of radiation
AGN often look different from different angles, sometimes hiding and sometimes revealing certain parts *NOTE: All galaxies have supermassive black holes at their center, but they only become AGN if they are "fed" |
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AGN Jets
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Jets of radiation eminating from the supermassive black holes at the center of AGN, usually powered by non-thermal radiation such as optical and radio emissions moving close to the speed of light
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Types of AGN
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Quasars
Radio Galaxies Blazars Seyfert Galaxies |
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Radio Galaxies
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Faint at optical wavelengths, don't have much of an accretion disk, and found mostly in elliptical galaxies
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Blazars
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Like radio galaxies, but the jet is viewed head-on
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Seyfert Galaxies
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Found mostly in spiral galaxies with lower luminosities than quasars
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Superluminal Motion
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The optical illusion when something appears to be moving faster than the speed of light
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Blackhole
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An object whose escape speed is greater than the speed of light
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Escape Speed
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Vesc = √[ (2 x G x M) / R ]
The speed required to just escape the gravitational field of another object |
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Orbital Speed
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Vorbit = √[ (G x M) / R ]
The speed an object needs to maintain in order to stay in orbit around another |
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Schwarzschield Radius
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Rsch = (2 x G x M) / c^2
The radius an object of mass M must have in order to be dense enough to be a blackhole |
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Special Relativity
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According to Newton, space is fixed and uniform and time passes at an unchaging rate, but not according to Einstein!
According to Einstein, relative motion effects our measurements of time and space |
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Basic Ideas of Special Relativity
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1. The laws of physics are the same for all observers as long as they are moving at constant velocities
2. Regardless of your speed or direction of motion, you will always measure the speed of light to be the same *NOTE: Space and time cannot be thought of as seperate entities - they are thus intrinsically linked |
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Length Contraction
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L = Lo x √[ 1 - (v^2 / c^2) ]
When objects move, their length contracts according to a stationary observer ("Moving sticks are shorter") |
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Time Dilation
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t = to / √[ 1 - (v^2 / c^2)]
Objects that are in motion appear to be experiencing a slower progression of time according to a stationary observer ("Moving clocks run slower") |
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Relativistic Increase in Mass
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M = Mo / √[ 1 - (v^2 / c^2)]
As an object accelerates, it aqcuires a larger and larger mass requiring a larger velocity in order to accelerate it In order to move something at the speed of light an infinite force would be required, thus explaining why no matter can move at the speed of light |
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General Relativity
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Based on the Equivalence Principle, which states that all objects in a gravitational field accelerate at the same rate independent of their masses
Additionally, the mass of objects alter the properties of space and time around them causing space to curve Gravity is thus curved spacetime and not a force |
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Structure of a Blackhole
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Composed of the Singularity at its center and surrounded by the Event Horizon at the length of the Schwartzshield Radius
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Singularity
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Central point in a blackhole where all the mass is crushed to a single point of infantescimal volume and infinite density
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Event Horizon
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Boundary through which nothing (no matter or light) can escape
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Three Properties of Black Holes
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Mass
Electric Charge Spin |
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Tidal Forces
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Differential gravitational force (different gravity is excerted on different parts of an object causing it to become squeezed and streched)
The larger the object (blackhole), the weaker the tidal forces because of relative distance to center |
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Hubble Law
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v = Ho x d
Signigicant because it demonstrates a linear relationship (evidence for expansion of the universe) and because it can be used to estimate distances simply by knowing velocity |
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Cosmological Redshift
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Zcos = (λ - λo) / λo
Caused by the expansion of space which carries objects along with it and elongates the wavelength of photons |
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Distance and Cosmological Redshift
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1 + Zcos = (d x t2) / (d x t1)
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Einstein's Cosmological Principle
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The universe is the same in all places and in all directions; on large scales, the universe is homogeneous and isotropic
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Dark Energy
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A mysterious form of pressure and energy whose nature is unknown
Similar to Einstein's idea of a cosmological constant because it counteracts gravity, but not similar to it because it doesn't balance gravity |
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Energy and the Fate of the Universe
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If total energy in universe is less than 0, then the universe is bound and it will collapse
If total energy in a universe is greater than 0, then it is unbound and will expand forever If total energy in a universe equals 0, then it is inbetween |
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Critical Density
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ρc = (e x Ho^2) / (8 x π x G)
The density of a universe that serves as the boundary between a bound and an unbound universe |
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Cosmological Mass Density Parameter
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Ωm = ρm / ρc
Used to determine whether a universe is bound or unbound and thus its ultimate fate. If greater than 1, universe is bound and if less than 1, universe is unbound |
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Age of the Universe
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To = 1 / Ho
The inverse of the Hubble constant gives an estimate for the age of the universe *NOTE: This is without including gravity (which causes expansion to deccelerate) or the possibility for dark energy (which causes expansion to accelerate) |
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Evidence that the Universe Expanded over Time
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1. Expansion of the Universe
2. Night sky is dark 3. Quasars indicate a period of great star-forming activity 4. Cosmic Background Radiation |
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Cosmic Light Horizon
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Encompasses the observable universe and includes everything we can see in the universe. There hasn't been enough time for the photons that are beyond this horizon to reach us.
*NOTE: Our distance to the cosmic light horizon increases as the universe ages |
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Cosmic Microwave Background (CMB)
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Provides evidence that the universe was once much hotter, denser, and more uniform than today suggesting that the universe began in a Big Bang
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Two Key Properties of the CMB
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1. Has a spectrum of a near-perfect blackbody, peaking at 1.1 mm in the radio part of the spectrum
2. Nearly isotropic (intensity of photons is almost the same in all directions) *NOTE: These indicate that the CMB photons originated from the universe as a whole and not from a specific source |
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Era of Recombination
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Important time in the early universe when the universe cooled and transitioned from being opaque to cosmic photons (absorbed them and they didn't survive) to being transparent (released them travel unimpeded across the univers)
Universe switched from a solid plasma to containing actual atoms, occuring when the universe was 380,000 years old and had a redshift of z = 1100 |
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Diapole Anisotropy in CMB
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The spectrum of the CMB is slightly blueshifted in the direction of Leo and slightly redshifted in the direction of Aquarius due to the motion of Earth through space in relation to the CMB
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Small Scale Fluctuations
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There are small wavelength shifts in the CMB from one spot to another that correspond to temperature differences
These fluctuations indicate the future origin of structure in the universe, shed light on the content of the universe, and give evidence about the curvature of space |
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Curvature of Space
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If the measurements of the small scale fluctuations in the CMB in dicate that they are greater than 1 degree on the sky, then the universe is spherically curved. If they are less than 1 degree, then the universe is hyperbolically curved. If they are equal to 1 degree, then the universe is flat.
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Total Density Parameter
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Ωo = Ωm + Ωrad + Ωde
Used to determine the shape and overall curvature of space *NOTE: This indicates that Dark Energy must exist and that it accounts for a large proportion because we can calculate Ωm and Ωrad with existing knowledge and still come up short. The amount of Dark Energy in the universe must thus be about 73%. |
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Evidence for Dark Energy
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1. Total Mass Density Parameter
2. Acceleration of the Expansion Rate |
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Contents of the Universe
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73% - Dark Energy
27% - Matter Of the matter: 23% - Dark Matter 3% - Baryonic Matter outside Galaxies 1% - Baryonic Matter in Galaxies |
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Origin of the Light Elements
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Occured 1-5 minutes after the Big Bang, forming deutirium, helium, lithium, and beryilium. Heavier elements did not form (as they do in stars) because this only lasted for a couple of minutes in the early universe.
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Inflation
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A brief period of superfast expansion that occured a fraction of a second after the Big Bang. Hypothesized to explain the Horizon problem (uniform temperatures throughout space) and the Flatness problem (disparencies in Ωo when total density of the universe rapidly decreases in very early times)
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Evidence for the Big Bang
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1. Abundance of the Light Elements
2. Expansion of the universe 3. CMB |
