On 13/04/2019 00:15, wrote:
Will a black hole in a galaxy ever consume their entire galaxy. If so
are there any known galaxies that are almost consumed by their black
hole?

No. It will only consume any stars that happen to venture too close and
find themselves in a tightly bound and ultimately decaying orbit. They
are not the deranged cosmic vacuum cleaners of science fiction.

Eventually it will consume all the material available to it and become
quiescent - visible only by the effect that it has on light passing by.

If our sun suddenly turned into a black hole then the planets would all
still orbit pretty much as they did before. I suspect Mercury would be
frame dragged a bit more but further out it would be business as usual
(apart from there being no sunlight any more).


In a spiral galaxy is it the black hole that causes the spiraling,
like water down a plug hole?

No. They are density waves of star formation in the galactic disk. There
are plenty of elliptical galaxies with no spiral structure as well.

Galaxy collisions can shake things up a lot - then when two massive
black holes merge you get very spectacular fireworks and gravity waves
that are detectable on Earth.

--
Regards,
Martin Brown