If the sun somehow collapsed to form a black hole, what effect would this event have on the orbit on the earth? (i) the orbit would be shrink; (ii) the orbit would expand; (iii) the orbit would remain the same size.

Answer 1

(iii) the orbit would remain the same size.

A black hole has no more mass than the original collapsed star, so the gravitational pull on the Earth would remain the same. Therefore, the orbit of the Earth would remain the same size.