[Dylan16807]

> 1. Assuming our calculations are wrong

That's what this is. We checked the math 20 times over and we know the model is wrong.

> 2. There is more interstellar dust/gas/solar-wind mass than we realize

We checked.

> 3. Heavier Black hole at center, or spinning speed/time dilation occurring?

Doesn't fit.

> 4. Effects of gravity are weaker at very long distances

Also an extraordinary claim, has not been ruled out.

Plus we already have confirmed 'undetectable' substances, so it's not very strange to suggest a new one.