Review

#01

Rotation curves, or determining orbits for binary galaxies.

#06

If two spirals collide, with their disks inclined to one another, the merger will have stars from one galaxy going around an axis, but the stars from the other galaxy going around a different axis, and so the combination will give the appearance of overall disordered stellar orbits. This could look similar to an elliptical.

On the other hand, if two ellipticals merge, and the merger is not a completely head-on event, then the motion of the two galaxies will be in a particular plane, and the merger will cause the stars to enter new orbits, to ``swirl'' about a common axis. This could look like regular orbits in a plane similar to that seen in spiral galaxies.

#08

There is no evidence for any major collision, but there is evidence that our Galaxy is ``swallowing'' up some smaller satellite galaxies (e.g., the Magellanic stream).

#09

As the name suggests, starbursts are galaxies that appear to have a large amount of star formation going on. They are frequently associated with collision or merger events (and evidenced by nearby galaxies, or other peculiarities in morphology). Mergers can lead to compressions of gas clouds that can stimulate globally a new generation of star formation.

#10

The galaxy must be moving through the space, and the gas outside the galaxy into which the jet is plowing, must have similar or greater mass than the gas in the radio lobes.

#11

Large masses in compact volumes, high luminosities, relatively rapid variability from small volumes, X-ray emission from compact cores, and the emergence of jets of fast gas from these cores.

#12

First, quasars are observed at rather large redshifts, corresponding to rather early times in the history of our universe. Second, it is reasonable that the messy process of making galaxies would allow for lots of gas to funnel into the galaxy core to be swallowed up by a black hole. Once a galaxy establishes its structure, less gas may flow toward the center, thereby ``starving'' the black hole, and shutting off the quasar behavior.

#14

The black holes would still be in galaxy centers, but if there is little gas flowing toward the black holes, the accretion disks can not shine brightly.

#15

The idea is that the formation of central black holes is rather common. Normal galaxies are just quasars for which the black holes have run out of fuel.