Modern cosmologists have stated a great many things as fact, which are merely inferred through mathematics, not actual observation.
The Standard Model failed to explain why galaxies hang together, so the mathemagicians were forced to invent a great attractor (black holes) to patch the theory.
When they came up with Dark Matter, they lost even lay people like me.
SagA* is our black hole.
They have a observed model of the star movement in the center of our galaxy showing there is a large mass there
16 years of observation...
https://m.youtube.com/watch?v=duoHtJpo4GY
Should be an update to it by now