There are many different branches of modern physics, including astrophysics, nuclear physics, biophysics, mathematical physics, as well as optical and laser physics. Physics is the study of matter and energy and how they relate and interact through space and time, which also includes more theoretical branches such as high-energy experimental physics.
Astrophysics is the branch concerned with the physics of the universe, including how planets, stars and other celestial bodies are created and how they interact with each other. Astrophysicists study such things as black holes, galaxies, supernovas and the expansion of the universe.
Biophysics is a relatively new field that combines physics and biology, which looks at such things as how brains, enzymes, proteins and other natural structures function. Biophysicists are primarily concerned with the physical reactions involved in various biological processes that occur in either animals or plants.
Mathematical physics is sometimes considered the basis of all physics, as the discipline wouldn't be possible without it. Optical and laser physics has resulted in some of the most important technological innovations such as X-rays, while nuclear physics is responsible for nuclear energy and nuclear bombs. High-energy experimental physics has branched out from nuclear physics, as it studies the reactions between matter and radiation.