White dwarf

A white dwarf is a dwarf star and the 'white' that was added to its name was just because, the few dwarfs that were found during their discovery appeared white--I'm not kidding, that's true.

Do you know how dense a typical white dwarf can get?

Well, if you don't, I can answer it for you: they appears in the size of our earth containing almost the entire mass of our sun. That's too much right?

Because of their smaller size and heavier mass these stars are extremely denser and compact objects having the average density approaching 1,000,000 times that of water.

To help you understand the way in which a normal star turns in to a compact white dwarf, let me explain to you the typical life cycle of a typical star.

A star takes birth when large amounts of near by gaseous particles--hydrogen atoms--attracted towards each other through the gravitational force, gets collided and coalesce--after much needed collisions--with each other to produce large quantities of heat along with some heavier compounds. The heat that got released during this process is much like a controlled hydrogen explosion, and is in fact responsible for the star to shine so brightly up in the space.

This heat got one more responsibility to look after: helping the star by restricting the sudden catastrophic gravitational collapse and thus maintaining a slow contraction process . Eventually there comes a stage where the star attains a perfect balance between the gravitational force, that which tries to contract the star even further, and the force that was caused by the heat energy, that which tries to explode the star out. And thus the star remains stable until one of its forces gets weaker, and we all know that it can't be the eternal gravitational force that gets weaker. The contraction process starts again and now the star reaches a stage where it was left with no fuel to burn anymore.

Supernova

There was a star somewhere around the sky staying almost unnoticeable, and got burst out suddenly in to a blistering brightness; it's just a one more Supernova!--if not Nova.

The energy and light that was radiated in to the sky during the star's sudden outburst is so heavy that it can easily outshines the entire galaxy--for several weeks to several months depending on the star's mass-- where it resides in, and that happens every time. The energy that got released during the process equals the entire energy that our sun can generate in its entire lifetime.

The star explodes and expels the material it was hiding till then, in to the surrounding Interstellar medium at a velocity of up to 30,000 km/s(10% that of light's). The material thus got released expands taking the help of a Shock wavethat was generated during the sudden explosion, in the form of gas and dust called a Supernova remnant.

Supernova happens very rare compared with Nova, which is a completely different process and happens very often. For a galaxy in the size of our Milky way, supernova happens just once in every 50 years. Anyways, it's a lot more common process and happens once in every sec, when we look through the entire universe(as the universe breeds stars every sec and they are not eternal).

It's not that every star that exists in the universe can eventually turn in to a Supernova, but is entirely depends on the mass of the star. A star that which reaches a mass that is greater than 1.4 times that of our sun's, at the end of it's fuel consumption, will explode in to a Supernova. And that 1.4 limit was found by Chandrashekar and hence named after him as Chandrashekar limit.

Our sun according to chandrashekar can't turn in to a supernova but will end up as a
White dwarf, when it gets completely devoured of its fuel. And even no possibility of forming a Nova or Supernova later on as there is no binary neighbor, close by.