 He explains how stars like the Sun keep their size due to the conflicting forces of gravity that pulls the gases in, and the expansion from escaping gases from the fusion reactions at its core.As the Sun ages, it will grow hotter and brighter to the point where the balance between these reactions will fail, causing the Sun to first expand into a red giant, and then collapse into a white dwarf, the collapse limited by the atomic forces.Tyson explains how larger stars may form even more collapsed forms of matter, creating novas and supernovas depending on their size and leading to pulsars.