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.
Now, what you think is gonna help the star from the catastrophic gravitational collapse??
--earlier it was stopped by the heat energy.
Well, its the outward pressure that was generated due to the repulsions between the sub atomic particles--electrons or neutrons or protons.
Here, the star that which attained balance through the repulsions between electrons is our required 'White dwarf' and the one that was supported by neutron repulsions is named as a 'Neutron star'
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