The short answer is: star shine because they are very hot. It is really no more complicated than that. Any object heated to thousands of degrees will radiate light, just like stars do.
A resposta breve é: as estrelan alumean porque están moi quentes. Realmente é máis complicado do que iso. Calquera obxecto quentado a milleiros de graos irradia luz, igual que as estrelas.