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Milky Way
Galaxies & Extra-Galactic Distances
Terminology
Dark Topics
Cosmology
100
This is where most of the Milky Way's stars are located. It's made of old & young stars, as well as vast amounts of gas and dust. Stars here orbit the galactic center in roughly circular orbits, and all move in the same direction.
What is the (galactic) disk?
100
- Made almost entirely old stars, low ISM - Shape of spheroidal or ellipsoids - No trace of Spiral Arms - w/ globular clusters
What are Elliptical Galaxies?
100
From the Greek (cosmos) Order + (logia) discourse; It's the study of Universe in its totality, its organization and evolution.
What is Cosmology?
100
A major discovery of the 20th century, clearly revealed by the rotation curve (orbital velocity vs. radius) of our galaxy, that most matter is not luminous matter!
What is Dark Matter?
100
Discovered in the 1960s by R. Wilson & A. Penzias, it's the radiation remaining from the Big Bang (the "heat" leftover). Present temperature is ~2.725 Kelvin.
What is the Cosmic Microwave Background (CMB)?
200
The area around the galactic nucleus, including the immediate areas above and below the plane of the galactic disk?
What is the (galactic) Bulge?
200
A neighboring galaxy, twice as big as the MW. It's predicted to merge with the MW in ~3.8 Byrs since it's blue shifted.
What is the Andromeda Galaxy?
200
The fundamental proposition that describes the Universal Galaxy distribution (on the largest scale) is Isotropic & Homogeneous.
What is the Cosmological Principle?
200
Believed to account for 23% of the Universe, it has been detected only indirectly, through the gravitational pull it exerts on visible matter and lensing effects.
What is Dark Matter?
200
The mass per unit volume enough to slow expansion to 0 @ t=∞. The relation between the actual density and this value determines the overall geometry of the universe; when they are equal, the geometry of the universe is flat (Euclidean).
What is Critical Density?
300
These long areas extend outward from the galactic center. Our solar system is located at the inner edge of one of these arms of the Milky Way--called the Orion arm.
What are Spiral arms?
300
The Small & the Large Magellanic Clouds are examples of this type of galaxy. They tend to: - have no regular shape - Chaotic w/relatively intense star-formation activity - w/both young (pop. I) & old (pop. II) stars
What are Irregular Galaxies?
300
Relationship between Distance & velocity of Galaxies; The more distant the galaxy, the faster it’s receding from us, leading to the conclusion of an Expanding Universe.
What is the Hubble Law?
300
Before Edwin Hubble showed Universe is expanding, Albert Einstein introduced this into his equations to produce outward pressure to counterbalance gravity.
What is the Cosmological Constant (Λ)?
300
Geometry of the Universe, in which the density ρ is so high, that the universe expands for several Byrs, then collapses under its own weight
What is a Closed Universe?
400
This is a large, dim, region that surrounds the entire galaxy. It is made of hot gas and likely lots of dark matter.
What is the Halo?
400
Technique used to measure extra-galactic distances out to ~8 Glyr away. It is one of the most precise methods since it relies on the explosion of a White Dwarf in binary system.
What is a Type Ia Super Nova?
400
Event when all matter w/in the Universe was concentrated in an ∞-simally small volume, @ roughly 13.8 Byrs.
What is the Big Bang?
400
In an expanding Universe, the Cosmological Constant represents a kind of Energy that accelerates the expansion.
What is Dark Energy?
400
A period of very rapid expansion predicted by the GUT (Grand Unified Theory) when forces separated, Univ. inflated by fact. Of 10^50×, Temp. dropped, and no curvature is apparent (like a flat earth).
What is Inflation?
500
The name of the center of our galaxy, which contains a supermassive black hole.
What is Sagitarius A*?
500
Technique to measure distances (to ~300 MLY) of Spirals Galaxies. It connects the ‘line broadening’ of 21 cm radiation to the Luminosity of a Spiral Galaxy. - The broader the line the faster gas is orbiting, and thus the more mass it has, to arrive at it's Luminosity using the M/L ratio.
What is the Tully-Fisher Method?
500
The galaxy supercluster that is home to the Milky Way. It was defined in September 2014, when superclusters were redefined according to the relative velocities of galaxies, and the Virgo Supercluster is now an appendage.
What is Laniakea?
500
A kind of exotic particle that has never been detected. These are defined to have interacted weakly with e&m radiation by congregating while Univ. was hot. It made gravitational traps, thus enabling galaxies to soon form.
What are WIMPs?
500
The satellite that has given us the most precise measurements of the characteristics of the CMB.
What is the Plank Mission (or spacecraft)?