Q& A: Black Holes

Q:
Do all black holes has to be massive objects? Do all black holes have to be dense?

A:
For the various types of black holes known to exist, see: http://chandra.harvard.edu/xray_sources/bh_midmass.html
If you were on a space ship that ventured beyond the event horizon of a supermassive black hole, it might not seem too different from ordinary space. However, that feeling would soon pass, as your spaceship would be pulled in a death spiral toward the center of the black hole in matter of a minutes.