Answer to Question 1
Black holes are gravitational vacuums, so much so that light cannot escape. Consequently, they are really difficult to see (hence, black hole). In order to look for them, we must look for hot matter emitting x-rays as it is being engulfed by a black hole. In and of itself, this means that we can only look for black holes that are not isolated, as we need to be able to detect whatever matter is near them as it is being sucked in in order to determine the location of a black hole.
Answer to Question 2
Spiral galaxies are flat, disk-shaped bodies with arms extending in a spiral out from the nucleus. Elliptical galaxies are spherical to rugby-ball shaped and include the biggest and smallest galaxies we have identified. Irregular galaxies are the least common, show no symmetry, and may be irregular due to gravitational distortion by a nearby massive body.
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