Am I Correct in Calling This Circular Reasoning? Are there any other fallacies here?
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Original Question
I've been thinking about the Dark Matter vs MoND debate since I've been seeing articles about it lately, and I learned about Dark Matter in college. Having had these explained to me a few times my understanding of the Dark Matter position boils down to this.
1. The motion of millions of stars is not following the laws of gravity as we understand them.
2. There must be "dark matter" that can only be detected with gravity.
3. We have a map of "dark matter" made using the gravitational lensing of millions of stars.
The above seems very circular to me. Nothing outside of gravity makes us suspect its existence, and nothing outside of gravity allows us to determine where it is. In other words, it seems to me like they can just put it wherever they want to justify that Dark Matter exists, since it can instantly explain everything that's off by being everywhere they need it, even though they used what they thought was off to decide where it is.
But when we add MoND into the equation, it gets worse. MoND is just a third layer to our theories of gravity (which seems much simpler and has the benefit of uniformity that dark matter would lack), but it doesn't explain the full data set quite yet, so this happens.
1. MoND doesn't explain all the data we see.
2. Dark Matter explains all of the data.
3. MoND has to be modified to explain 100% of the data, and since it can't, Dark Matter should be the accepted model.
There is something very troubling about this, and I spoke with someone more knowledgeable than me on the topic to make sure it wasn't gaps in my understanding, since I'm not a career astrophysicist, and in his opinion, this assessment is correct, and I know that doesn't mean I'm right, but I think it means I'm making a reasonable assertion. Is there a word for this second fallacy? Something seems to have been made up and made king, and because something more realistic can't compete with made up, it loses the argument.
Are there any other fallacies here that I'm missing? Or am I using any fallacious reasoning?
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This is difficult to answer without understanding the content (i.e., knowing what MoND is). For the first line of reasoning, at least, I feel there is some question begging (begging the question ) going on in that it is assumed that gravity is still relevant rather than some other unknown force. But again, I would not confidently argue this because I do feel that a better understanding of the content is required.