Quantum physics solves this! Quantum tunnelling allows a particle to cross a classically impenetrable barrier (the repulsion between the protons in this case) provided that it does this over a short enough time period. This is a consequence of the uncertainty principle. read more
Because astrophysics is a very broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics. read more
Quantum physics is necessary to understand the properties of solids, atoms, nuclei, subnuclear particles and light. In order to understand these natural phenomena, quantum principles have required fundamental changes in how humans view nature. read more