Term
| What is the Cosmological Principle? |
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Definition
The universe is homogenous (appears the same in every location) and isotropic (and every direction) on large scales.
- the properties of the universe are the same for all observers
-the universe looks the same no matter whoever or wherever you are |
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Term
| What is the Hubble equation and what are the units of Ho? |
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Definition
v = Ho d
Ho = acceleration/size
the Hubble constant is km/s so if your answer is 40,000 km/s/Mpc, convert that to 40 km/s. |
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Term
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Definition
| where the wavelengths are longer than normal, hence shifted to the red end of the spectrum. |
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Term
| How is look back time, redshift, and distance related? |
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Definition
| When an astronomer looks at a distant object, the distance in light years between him and that object relates to the look back time. If the object is 40 light years away, he is looking back 40 years in the past. The larger look back time, the larger the redshift. |
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Term
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Definition
13.7 x 10^9
or 1.37 x 10^10 |
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Term
| what is the difference between expansion and acceleration? |
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Definition
expansion ( +/- Rdot) is when the universe is getting bigger, the space between objects are increase.
acceleration (+/- RdoubleDot) is how fast the universe is expanding.
you can have a universe thats expanding but decelerating (at a rate slower than yesterday) |
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Term
| What do large scale structures tell us about Cosmology? |
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Definition
| Large scale structures tells us how matter was distributed at the beginning of the universe by measuring and modeling the matter in the universe. |
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Term
| How do we determine large scale structure? |
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Definition
| By measuring and modeling the matter in the large scale universe |
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Term
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Definition
| This is how bright it should be, this is how bright it is = you know the distance. |
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Term
| What measurements led us to believe the universe is expanding? |
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Definition
| The measurement of redshifts from distant SN |
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Term
| How have galaxies evolved over time? |
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Definition
| Galaxies at high redshift are "active", newer galaxies are "normal." |
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Term
| What is the cosmological principle? |
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Definition
| Universe is homogenous and isotropic on large scales. |
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Term
What does it mean to be homogeneous?
What does it mean to be isotropic? |
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Definition
homogeneous is when everything is the same at any location.
isotropic is when everything is the same in every direction. (universe is centered on my point) |
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Term
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Definition
When the wavelength of photons are elongated due to expansion of the universe.
Doesn't mean high or low energy, just higher or lower energy compared to the before-shift. |
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Term
| When an astronomer looks at a distant galaxy, how are redshift, lookback time and distance related? |
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Definition
| The larger the redshift, the further back in time you're looking because the distance the photon has to reach you is longer. |
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Term
| Why does an accelerating universe imply the existence of a cosmological constant? |
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Definition
| Because without the cosmological constant, the only force in the universe is gravity, which is attractive and can only decelerate the universe. |
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Term
| What measurement leads us to believe that the universe is accelerating? |
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Definition
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Term
| What is the Cosmic Microwave Background (CMB)? |
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Definition
A uniform signal from every direction of space in microwave lengths.
perfect BB/thermal radiation |
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Term
| Why does CMB exist? What event caused it? Why did it happen? Why did it stop? |
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Definition
When the universe was young, pre stars and galaxies, it was dense, very hot, and filled with protons and electrons which gave characterized it as a foggy plasma. Eventually, the universe was expanded to the point where the protons and electrons were unable to collide with one another, so instead they bound together to form Hydrogen (aka Recombination) and the universe became transparent.
The CMB exists from the stage where the universe went from opaque to transparent (recombination) about 300,000 years after the Big Bang when the universe was about 3000K. |
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Term
| Why is the CMB the temperature it is now? |
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Definition
| Recombination occurred at 3,000K. The red shift is 1000 so now we measure the temperature at 3K |
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Term
| How do the fluctuation in the CMB relate to the structure of the universe today? |
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Definition
| The CMB is extremely uniform with a 1:100,000 fluctuation ratio. This little bit of extra matter represents where the clusters form today. Seeds of large scale structure |
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Term
| what does CMB tell us about the curvature of space |
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Definition
| Tells us K = 0, space is flat. Om = 1 |
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Term
| What is Big Bang Nucleosynthesis? |
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Definition
BBN: conditions just right for fusion to occur everywhere
- refers to the production of nuclei other than Hydrogen (1p) during the early moments of the big bang. BBN happened 3 minutes after BB, not exactly at the moment, because the temperature was too hot that the protons and neutrons were not stable and fusion couldn't happen. |
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Term
| Why did BBN happen/Why did BBN stop? |
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Definition
| It only lasted a few minutes because the temperature/density was once at a sweet spot, until expansion caused the temperature and density of the universe fell below that which is required for nuclear fusion. |
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Term
| What elements did BBN produce? |
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Definition
Lots of Hydrogen
Some Helium
Little deuterium |
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Term
| What does BBN tell us about baryons in the universe? about all matter? |
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Definition
Since baryons undergo fusion via the strong force, by calculating the amount of deuterium created by the BBN, we are able to know Om(b) = 0.4
BBN tells us NOTHING about all the matter in the universe because some matter may not interact with the strong force |
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Term
| What are the three cases for the standard model? |
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Definition
Omega > 1, k = +1, positive, universe is closed (re-collapse)
Omega = 1, k = 0, flat, expand forever
Omega < 1, k = -1, negative, expand forever |
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Term
| Why do large scale structures tell us about cosmology? |
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Definition
| Tells us the organization of galaxies and galaxy clusters and the filaments formed by gravitational collapse. Tell us about the battle between gravity and expansion. |
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Term
What do large scale structures tell us about dark matter?
**Need better explaination... |
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Definition
| In order to get galaxy rotation curves and simulations accurate on a computer, there needs to be an accurate amount of dark matter. Enough amount that the structures collapse but not too much and not too little. Dark matter has to be non-baryonic (WIMPS) in order for the structures to collapse before CMB. |
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Term
| What does large scale structure of the universe look like today? |
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Definition
| Looks like stringy, fibrous, filaments. |
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Term
| How do we determine large scale structures? |
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Definition
| Through galaxy surveys. We measure the redshift of the galaxies in the sky. |
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Term
| What are the different types of quasars,**how have quasars evolved over time, why can you see fewer quasars at z=0 versus z=2, and why are there very few nearby quasars? |
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Definition
Normal: when light that comes out of galaxy can be explained by adding starlight from all stars
Active: when something else is putting out more energy than the stars combined.
-for instance, SMBH in center, material fall and heat up, emitting light in a jet
Quasars have time to form at z=2, but the surrounding materials all fall into it's SMBH and once all the material is gone, quasars cease to exist.
There are few nearby quasars because you can't separate distance and look back time. You can look at a nearby quasar and see what it looked like at, for example, z = 2. |
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Term
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Definition
| A region with a lot of galaxies. On a bubble-size scale, galaxies aren't homogeneous or isotropic, but do look more distributed on a larger scale. |
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