Amber Reed's Quiz

1.     What are the three major types of galaxies?
lenticular Galaxy:has a disk like a spiral galaxy but much less dusty gas(intermediate between spiral and elliptical)
Elliptical galaxy:a spheroidal component,virtually no disk component
irregular galaxy:neither spiral or elliptical. 
Spirals have both disk and spheroidal components; ellipticals have no disks

2.     How are galaxies grouped together?
spiral galaxies are often found in groups of galaxies(up to a few dozen galaxies per group). elliptical galaxies are much more common in huge clusters of galaxies(hundreds to thousands of galaxies). Spiral galaxies tend to collect into groups of up to a few dozen galaxies. Elliptical galaxies are more common in large clusters containing hundreds to thousands of galaxies.

3.     How do we measure the distances to galaxies?
We can measure distances greater than 10 billion light years using white dwarf supernovae as standard candles. 

4.     What is Hubble's law?

Before Hubble, some scientists argued tat "spiral nebulae" were entire galaxies like out Milky Way, whereas there scientists maintained they were smaller collections of stars within the Milky Way. The faster a galaxy is moving away from us , the greater its distance. Hubble settled the debate by measuring the distance to the andromeda galaxy using Cepheid variables as standard candles. Hubble also knew that the spectral features of virtually all galaxies are redshifted=> they're all moving away from us.By measuring distances to galaxies, Hubble found that redshift and distance are related  in a special way.

5.     How do distance measurements tell us the age of the universe?
Hubble's constant tells us the age of the universe because it relates  and distance of all galaxies.The expansion rate appears to the same everywhere in space. Cosmological principle: the universe looks about the same no matter where you are within it.  Matter is evenly distributed on very large scales in the universe. 

6.     How do we observe the life histories of galaxies?
Deep observations of the universe are showing us the history of galaxies because we are seeing galaxies as they were at different ages.
7.     How did galaxies form?
Matter originally filled all of space almost uniformly. Gravity of denser regions pulled in surrounding matter. Denser regions contracted forming protogalactic clouds. H and He gases in these clouds formed the first stars. Supernova explosions from he first stars kept much of the gas from forming stars. Leftover gas settled into spinning a disk.

8.     How do galaxies differ?
Observations of some distant red elliptical galaxies support the idea that most of their stars formed very early in the history of the universe.We must also consider the effects of collisions. Collisions were much more likely early in time, because galaxies were closer together. Many of the galaxies we see at great distances do indeed look violently disturbed.The collisions were observe nearby trigger bursts of star formation .Some of the differences between galaxies may rise from the conditions in their protogalactic clouds.

9.     What are quasars?
If the center of a galaxy is unusually bright, we call it an active galactic nucleus. Quasars are the most luminous examples.Galaxies around quasars sometimes appear disturbed by collisions.

10. What is the power source for quasars and other active galactic nuclei.?
The only model that adequately explains our observations holds that supermassive black holes are power source. Jets are thought to come from twisting of magnetic field in the inner part of the accretion disk.