  We give the comment why the supermassive black hole exists at the center of
almost all galaxies. We consider the origin of the supermassive black hole from
the point of view of the density of the matter. If the density of the matter is
fixed and such matter can come together by the gravitational attraction, such
stellar object eventually becomes the black hole. If the density of the matter
is that of the atom, such matter naturally comes together to form the black
hole by the gravitational attraction. This is expected to be the process to
form the supermassive black hole. In this way, we can understand that there
exists supermassive black hole at the center of almost all galaxies, because
there is no delicate process to evolve into the black hole.
