Novae

What is nova? What is the mechanism behind a nova? Why are novae sometimes recurrent?

Most of stars shine steadily. Meaning the brightness of these stars does not change. But there are some stars whose brightness changes dramatically in over very short period of times. These stars are called nova. The brightness of these stars increase enormously (sometimes 10,000 times) and slowly dims again.

Novae are formed form the explosion of white dwarfs. If a white dwarf exceeds Chandrasekhar mass, the pressure of electrons in the interior of dwarf cannot withstand the gravitational pull, and the star starts to collapse. The temperature inside the star rises so rapidly that carbon fusion begins everywhere throughout the white dwarf. This causes the entire star to explode and become supernova. 

If the novae do not get rid of all matter, it can be recurring. Novae recur when the distance between two stars is close enough for dwarf’s gravity to pull hydrogen and helium.