That is why, in this article, it is of our particular interest to present the differences between a nova and a supernova, based on their brief definitions.
A nova is a star that suddenly brightens dramatically and then slowly fades, but may continue to exist for some time. A nova increases to several thousand times its original brightness in a matter of days or hours. Then, it enters a transition period, during which it gradually fades and brightens again.
This happens as a reaction between a white dwarf star and a red giant or evolved star. In this sense, the gas that makes up the giant is attracted by the gravity of the dwarf and after a long period of time, a detonation occurs that gives rise to a thermonuclear explosion. The star that remains is a white dwarf, subject to a continual depletion of matter in favor of the larger star.
This phenomenon happens with dwarf novae, which arise again and again at regular intervals. Novas are late-evolving stars that explode because their outer layers have formed excess helium through nuclear reactions and it is expanding too fast to be contained.
Similarly, a supernova is a star that suddenly brightens dramatically and then slowly fades. After the explosion, the stars are usually completely destroyed because they are not able to withstand gravity. In this aspect, supernovae are about 100 times brighter than novae. Similarly, these explosions can be brighter than the galaxies in which they occur.
Very large stars explode in the later stages of their rapid evolution, as a result of gravitational collapse, when the pressure created by nuclear processes can no longer support the weight of the outer layers and the star explodes. When it occurs in this way, it is called a type II supernova. On the contrary, when the explosion occurs in the same way as a nova but there are almost no residues of it, it is called a Type I supernova.
After the explosion of a supernova, it can lead to the formation of a black hole (a finite region of space with a gravitational field so strong that not even electromagnetic radiation can escape its proximity, falling inexorably into the hole), due to the magnitude of the explosion.
As seen in the previous statements, the differences between nova and supernova can be summarized as:
- After a nova explosion the star may continue to exist as a so-called white dwarf star while after a supernova explosion little remains except the expanding shell of gases.
- After a nova explosion, different remnants of the star are dispersed, including a large mass of gases, but a black hole does not form, whereas when a supernova explosion occurs, a black hole is formed.
- The supernova explosion is much larger and more intense than a nova explosion.