as noted in the post of 8-06-07, a black hole can
spew energy and material in twin jets traveling in
opposite directions along its axis of rotation

the material in these jets exits the black hole at
a speed close to that of the speed of light; and it
moves hundreds of thousands of light-years beyond
the galaxy

the jets serve to redistribute matter and energy
across the universe, and in this sense, they are
constructive

they are also destructive in that to be in their path
is analogous to finding yourself in the path of a
flamethrower; a black hole's jets can wreak havoc
in and around its galaxy

at this time, the supermassive black hole at the
center our galaxy does not emit jets; but events
are underway that will eventually lead to their
return

these events are described in the video below,
an excerpt from NOVA's The Monster of the Milky Way