If you're interested in becoming an astrophysicist, you'll need to pursue a degree in astronomy or astrophysics. After that, you'll need to pursue specialized postgraduate studies, usually a PhD, to get a position as a professional research astronomer. It's important to note that this process takes time - you'll need four to six years just to get a bachelor's degree, and then graduate school can take anywhere from five years for theorists to seven or eight for experimenters and observers. After that, you'll likely need two or three postdoctoral research appointments before you're ready for a teaching job at a major research university. In addition to the time commitment, it's important to understand the breadth of knowledge required for an astrophysicist.
Astrophysics is a very broad subject, and astrophysicists must apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
