Jody

Thank you very much for your detailed answer! You've clarified everything for me. And yes, I should search more about the "non-tenure tracked astrophysics positions". I do not know much about that yet.

Thank you, I edited my post correspondingly. I should have put more emphasis on "not continuing in the same field".

I want to go for a PhD because I like to do research. But there are too few faculty positions in the academia, and I can't afford to spend my whole life struggling on the tenure track. So I plan to sharpen my technical abilities that I will use in getting the PhD, and after I graduate use them to apply for jobs in the industry. For example, I want to go to grad school in Astrophysics, in which I will practice skills in computation and statistics, and then go to the industry (maybe finance or something, because there isn't really an industry in the astrophysical studies). Is this acceptable to schools? Should I say this outright in my SOP, or should I conceal this motive entirely?