>> Newtonian gravity calculations are quite spot on

Which is why the concept existed long long before any talk of relativity or time dilation, back before anyone knew the name Einstein. (He was like 4yo when this came out)

From American Physical Society: "the true “father” of the black hole concept was a humble 18th century English rector named John Michell–a man so far ahead of his scientific contemporaries that his ideas languished in obscurity, until they were re-invented more than a century later."

https://www.aps.org/apsnews/2009/11/1783-john-michell-black-...