Galactic black hole origins?

I realize that a “Regular” black hole is created when a star of over 3 solar masses colapses under its own gravity.

Where do the giant black holes of thousands of solar masses at the centers of galaxies come from?

[Duplicate thread. See http://boards.straightdope.com/sdmb/showthread.php?threadid=92991 ]

[Edited by bibliophage on 10-14-2001 at 11:22 AM]