Stars (simple version)

Stars

The stars are the most common objects in space, being all over the universe. They are formed by clouds of matter called nebula, which are mostly made of hydrogen and helium. With the evolution of the star formation process, a corps known as protostar is formed. As more matter is added to the protostar, its mass is increased, until the process of nuclear fusion starts, setting the end of the matter addition to the so formed star.

At school we learn in chemistry that for a reaction of combustion to occur it is necessary fuel and oxidizer (usually oxygen). Then the question comes up:

--If there is no oxygen on the Sun then how is all the heat produced?

The answer is in the nuclear fusion phenomenon which is given by quantum effects (explained by quantum mechanics). On this process, atoms bound together, forming a heavier element and releasing a great amount of energy in photon form (the radiation we receive on Earth).

The hydrostatic balance is one of the most important subjects in order to understand the behavior of the stars. When a star initiates its nuclear fusion, a balance between gravity (which induces a contraction) and degeneracy pression (which induces an expansion) is created, preventing the star from collapsing due to its gravity.

The destiny of each star depends upon almost exclusively one factor: the mass. According to the star’s mass, it may later become a white dwarf, a neutron star or even a black hole. Stars less massive than the Sun go through a common process when they are near “death”, spreading a huge amount of matter in a massive explosion called supernova. The residual of the star (after explosion) varies according to its mass, possible being a white dwarf, a magnetar, a black hole and so on.

Reference link: https://www.if.ufrgs.br/oei/stars/formation/form_st.htm