Images of colliding galaxies

Originally posted by Fred Ryan
"Dear Mr, Ryan,

Thanks for your note below. Contrary to popular suspicion, what
matters is not ideas. Ideas are a dime a dozen.

What matters most are testable predictions of unknown phenomena
derived from those ideas If you produce such a list of predictions
from your ideas I will be happy to offer comment.

Thank you for your interest ...[text shortened]... niverse theory? After all, he does say that galaxies are believed to be moving in orbits.

I still don't understand what your theory is.

Can you explain it in more detail?

Originally posted by Fred Ryan
I seem to look at this in a simple way. The stars tracked in orbit around what was prematurely termed a Super Massive Black Hole, orbit the center of their galaxy more often than those stars in the periphery.

What you don't seem to understand, is that gravity works both ways. Objects rotate around their common centre of gravity, not around a given object. It only appears that way when one object is significantly more massive than the rest.
So you seem to be observing rotation about a point in space and assuming that suggests the existence of a massive object at that point - which it doesn't.

Scientists know that certain phenomena such as galaxies, clusters etc are are rotating around a given point in space, and that that point in space is therefore the centre of gravity. When they cannot find all the matter to explain the given rotation, they term the unknown matter 'dark matter' because they cant see it. But there is no immediate reason to believe the unknown matter is at the centre, and in fact there are ways to determine whether or not it is at the centre by observing the motion of bodies, and it has already been pointed out in this thread that for the case of the galaxy, such motion suggests that dark matter is in a cloud throughout the galaxy - not at the centre.

Originally posted by twhitehead
What you don't seem to understand, is that gravity works both ways. Objects rotate around their common centre of gravity, not around a given object. It only appears that way when one object is significantly more massive than the rest.
So you seem to be observing rotation about a point in space and assuming that suggests the existence of a massive object ...[text shortened]... ch motion suggests that dark matter is in a cloud throughout the galaxy - not at the centre.

However most if not all galaxies do appear to have a massive black hole in the centre.

With something like 0.2% of the total stellar galactic mass.

Originally posted by googlefudge
However most if not all galaxies do appear to have a massive black hole in the centre.

With something like 0.2% of the total stellar galactic mass.

Which suggests that we are able to determine its mass based on the motion of the stars around it?

Originally posted by twhitehead
Which suggests that we are able to determine its mass based on the motion of the stars around it?

Basically yes, although it gets more complicated for extra galactic black holes.

The one in the centre of our galaxy has several stars orbiting it at a significant fraction of
the speed of light, which gives us a very good handle on it's mass. (about 4.1 million solar
masses, in a volume of about 6.5 light hours across)

The fact that black holes in the centre of galaxies appear to have a mass proportional to the
mass of the galaxy they are in suggests that they form with the galaxy and don't form first and
then form a galaxy around them.

Theory and modelling seem to agree with this and suggest mechanism's for it, however the science
is far from certain.

Originally posted by twhitehead
What you don't seem to understand, is that gravity works both ways. Objects rotate around their common centre of gravity, not around a given object. It only appears that way when one object is significantly more massive than the rest.
So you seem to be observing rotation about a point in space and assuming that suggests the existence of a massive object ...[text shortened]... ch motion suggests that dark matter is in a cloud throughout the galaxy - not at the centre.

Scientists know that certain phenomena such as galaxies, clusters etc are are rotating around a given point in space...

Where would I begin to find these scientists? Everywhere I've looked so far has ended with, scientists think galaxies orbit each other. I haven't found anyone who think clusters of galaxies are in orbit and if such scientists exist, then there's the information I need. I just need to know who they are and then I'll find out what they used to form that opinion.