Indirectly breaking the speed of light Imagine a system of two objects: a supermassive black hole mass of approximately $10^{36}$ kg and another $1$ kg object revolving around the black hole with an average mean distance of about $1.5×10^{8}$ m. The angular velocity of the smaller object is $2$ rad/s and correspondingly the linear velocity is equal to the speed of light. But how could this be? I know this might be wrong, but where?
 A: A black hole of mass $10^{36}$ kg would have a Schwarzschild radius (the distance from the center to the event horizon) of about $1.5\times 10^{9}$ m.
So your choice of "orbital" distance is inside the black hole, and it won't orbit, it will just fall inward.  Outside the event horizon there is a minimum distance for a stable circular orbit which is three times the Schwarzschild radius.
You cannot use Newtonian physics for these calculations; you need full blown general relativity.  If you try mixing these two systems together you get nonsense.  It is only at distances where the gravitational field is weak that you can apply Newtonian physics with good accuracy.
Regarding why we are so confident that we know what happens inside a black hole (like everything falling inward) when we can never test that directly it comes down to the way the theory is designed.  The theory for what happens outside the event horizon and inside the event horizon are the same theory and as we have verified that theory for outside the event horizon to a very, very high level of confidence so there is a very high level of confidence in it's predictions for inside the event horizon.  The basic core the theory of general relativity is that physics must work the same way everywhere.  The event horizon doesn't make any difference in this sense.
A: If you imagine a system that breaks the speed of light, it can't exist in reality; simple as that. At gravitational fields that strong, you can't use the Newtonian approximation to determine orbit speeds and must use general relativity instead.
