I’m wanting to write a realistic sci-fi book but there are a few concepts I don’t understand how to apply. I’m not good with physics so what I’m wanting to know is how to calculate what pressure and temperature would be required for sustained nuclear fusion for something comparable to a star shrunken down to a few meters in width or would something that size and pressure cross the Schwarzchild radius and create a black hole? Also any tips on calculating things like time dilation at relativistic speeds. I’m a history major but I have a layman’s knowledge of some theoretical physics and am very interested in it. Thanks!