Part 1 Flashcards
Alternative unit to the solar mass unit:
Parsec (pc)=
- 261 light years=
- 086 x 10^16m
Our galaxy:
Disk radius?
Disk thickness?
- Our galaxy rotates slowly and differentially~
R= 12.5 kpc (10^3 pc) Thickness= 0.3 kpc.
- We are located about 8 kpc from the center.
Nearest Galaxies:
LMC (Large Magellanic Cloud)~ A small irregular galaxy located about 50 kpc from the sun.
Andromeda Galaxy~ The nearest galaxy with a size comparable to our own galaxies, located about 770 kpc away from our sun.
Megaparsec (Mpc)~
Equal to a million parsecs and is a cosmologists favored method of measuring distances because it is roughly the separation between neighboring galaxies.
1Mpc= 3.086 x 10^22 meters.
The Coma Cluster~
Located about 100 Mpc away from our galaxy. It contains perhaps 10,000 galaxies.
Field Galaxies~
Galaxies that are not part of a cluster, which includes the majority.
Microwaves:
- Discovered by… When?
- Blackbody spectrum temperature?
- Penzias and Wilson. 1965.
- 3 Kelvin. (2.725 +/- 0.001 Kelvin)
•extremely close to the “blackbody form”
-Studied by the FIRAS (Far InfraRed Absolute Spectrometer) and by the COBE (COsmic Background Explorer)
Infrared:
- First surveyed by..? When?
- Uses in cosmology?
- The IRAS (InfraRed Astronomical Satellite) in the ‘80’s.
- Used to spot young galaxies where star formation is in the early stages.
•Extremely useful at peering through the dust in our galaxy to see distant objects, most notable near the galactic plane region which is highly obscured by dust.
•Vital for studying the most distant galaxies whose emission has shifted predominantly to the infrared part of the spectrum.
X-Rays:
- Uses..?
Useful in probing galaxy clusters which are usually surrounded by gas so hot (tens of millions of Kelvin) that it emits light on the x-ray part of the spectrum. The gas is though to be a remnant of the formation of galaxies, which failed to collapse to form stars.
Radio Waves:
- Uses..?
- A powerful way of gaining high resolution maps of distant galaxies.
• A powerful future probe will be the observation of the ‘21 cm’ emission line, due to the spin-flip of the electron in a hydrogen atom, enabling maps of the distribution of neutral hydrogen gas in the distant universe. -this will be a good way to probe the early development of structures in the Universe and its transition to its present state of high ionization of the intergalactic medium.
Homogeneity~
The statement that the Universe looks the same at each point.
-not necessarily indicative of isotropy.
Isotropy~
States that the Universe looks the same in all directions.
-not necessarily indicative of homogeneity, unless we require that a distribution is isotropic at EVERY point, in which case it does enforce homogeneity as well.
The Expansion of the Universe~
Everything in the universe appears to be moving away from us and the farther away an object is, the faster its recession seems to be. This is measured vis the “redshift” (ie. Doppler effect applied to light waves).
•blueshift~ higher frequency, (moving closer)/ redshift~ lower frequency, (moving away).
-This technique was first used by Vesto Slipher around 1912 and was later applied by Edwin Hubble.
Redshift Formula~
Z= λobs - λem/ λem
λem and λobs~ wavelengths of light at the points of emission (the galaxy) and the observation (us).
So if a nearby object is receding at a speed of ‘v’, then its redshift is…
Z= v/c; (‘c’ being the speed of light).
Hubbles law:
- Hubble noticed that the velocity of recession was proportional to the distance of an object from us.~
V= H0r.
Nearby galaxies exhibit abnormal/random motions known as “peculiar velocities”. Nearby galaxies have the smallest velocity relative to our own.
