Is this PhD going to be in physics? There are many applications than teaching (which is good, because there are far more people who want to teach than there are faculty jobs for them anyway). There are jobs in industry, research and development, for the government and government contractors, national labs, finance/Wall Street, and more. And most of those tend to pay better than academia.
No, you don't pick a PhD topic from a list. At least I don't know anyone who's had that experience in physics/astronomy. You would want to have a general idea about the field you're interested in before picking a grad school (some of them have very specific specialties). When you get to grad school, you'd get to know the professors and figure out who you might be interested in working with (your choice of adviser can have a bigger impact on your grad school experience and job expectations than your choice of field). You and the adviser would figure out what topics interest you and what they could supervise you in, as far as their own knowledge or resources go.