Pick up an intro physics book, something on the calc-based level, and know it cold after studying. A lot of programs will accept different majors, but they usually are engineering, math, or other sciences. I understand the fascination, that's why we all got into it. However, if you can even get in with an econ major and no physics classes ever, you should know this is not for the faint of heart. You need to take a few physics classes to experience real physics, because a lot of people who go into physics as an undergrad don't come out as physics majors. It's not what you see on TV, or even read in all those best selling bull crap books. Oh, and IMHO, anything with the word astro in front of it makes it even harder to get into because funding is much smaller, so even decent apps in physics have trouble getting into astro or astrophysics programs.
Agreed. Apply to physics programs that offer astronomy research.
Hi, I'm an Economics major with a strong math background (minor in mathematics).
I have never taken physics.
However, for curiosity's sake, what would I need to study if I were to intend taking the PGRE?
I'm curious because astrophysics absolutely fascinate me and I have located several graduate programs which will accept any major given that their PGRE is high enough.
I imagine it would be difficult for me to properly prepare myself, but I have never been one to shy away from sheer challenge.
I'm confident in my ability as an astro data guy to handle economics, so don't let anyone scare you away from doing physics/astro if that's where your heart is--there's a lot in common. As long as your econ major was math-based (calc-based stats and Calc 3 are a must), you'll be fine once you actually get to research. As others have said, your main hurdle will be the actual PGRE; aim for an 800 (domestic) or 900 international, since you have a point to prove. That should be enough to get you into a good program to let you pursue what you love. Even a 600-700 though is probably enough to convince someone to take you on. Once you start your degree, your actual score won't matter, and you'll be so involved with your research it won't matter than you haven't a clue how to find the electron orbitals of a hydrogen atom or the inductance of a solenoid. If a school accepts you they'll understand they'll have to work with you in classes, you'll probably sit in a few upper-level undergraduate classes and take your quals a year late.
Alternatively, and this actually might be easier, see if there's someone at your school/alma mater who would be interested in taking you on as an unpaid researcher in the physics department (I doubt you'd get funding). Doesn't have to be astronomy, but I'd pick something data oriented, since it'll translate better. You'll spend less time talking about rings and complex analysis, and more time working on standard deviation and error (risk) analysis. Do this and schools will care less about your PGRE, plus you'll have a ready-made LoR (most of your econ profs won't know how to write a science LoR). Put in 40 hrs/week for 12 weeks on a project like this, and you'll both know if you still want to do it and you'll have the in you need to get accepted somewhere.