Is dark matter an assumed fact by all astronomers?

To my knowledge, it's an accepted truth that *something* is holding galaxies together despite the faster-than-should-be orbital speed of it's stars. As gravity is the only force we're aware of capable of holding things in orbit, there must be something causing the excessive gravity.

Hmmmm.... the alternative would be a new, unknown force, *acting* like gravity...

There is no such thing as an assumed fact. Either something is a fact or it isn't.

The idea about dark matter came from observing that stars orbit galactic centers FASTER than they should given the observed (luminous) matter. So it appears that there is more matter there, creating an gravitational field which is more intense, and therefore requiring the observed velocities. Since this extra gravity is expected to be created by matter which is not seen, they use the term "dark matter". They don't see what does it, they only see its effects.

When I first started reading articles in Scientific American in the early 1960's astronomers didn't even have a NAME for what was making spiral galaxies rotate like a now old fashioned phonograph record on a turn table does. The name given to whatever it is that is making galaxies (not just spiral galaxies) is "dark matter."

As Satan Claws tried to explain, there is no such thing as an "assumed fact." A scientific "fact" is NOT a fact until it is confirmed by multiple observations of the same phenomenon over time. Like many non-scientists, you are confusing subjective "truth" and assumptions with factual scientific or mathematical, logical "truth"/"fact."

It comes from the assumption that it must be the force of gravity keeping the stars together in a galaxy, but there is another possibility that doesn't require any new exotic forces or forms of matter to be posited...

Electromagnetic forces, i.e. the forces that result from electric charge separation, are believed by plasma cosmologists to hold even greater influence than gravity...

http://www.plasmacosmology.net/

Here is a good documentary about plasma cosmology:

http://video.google.com/videoplay?docid=4773590301...

It is difficult to accept a fact if you don't see it. Astronomy use telescope to see the stars,they cannot observe a star with a microscope.

Only cosmology interprets what astronomers see or don't see.