White Dwarf (Star)

White Dwarf captured since space simulator SpaceEngine.

A White Dwarf is a kind of "Compact star", it is formed by main sequence Star whit a similar mass to the Sun (Yellow Dwarf).
White Dwarf is a object with stellar mass and with a similar diameter of a terrestrial planet, therefore, it's a object very dense and its gravitational field is very strong.

White Dwarfs are among the most abundant stars, are part of the life cycle of a star of less than 10 solar masses. They consist of stars that have merged all its hydrogen atoms in their life cycle, and cannot make further thermonuclear mergers that allows them to release energy as light and heat, then they cooled and the pressure gas isn't enough to keep all the mass of the star and this begins to collapse under its own weight, the matter of the star is compressed so that this reaches similar size to earth but with the mass of a star.

Life cycle of a dwarf star and a massive star.

Sirius B, The closest white dwarf captured with SpaceEngine:

Black Hole

Black Hole near a star cluster captured whit SpaceEngine.

A stellar Black Hole is a "Compact Star", it has a mass greater or equal to 2.5 M☉ (greater to 2.5 times the mass of the sun), and has a diameter of a few kilometers, therefore, is a extremely dense object,  this means it has an extremely strong gravitational field, so that everything that gets close enough to this is trapped by its field and is absorbed.

Black Holes have a very dark color, but they´re not completely black, this is due to emissions of Hawking radiation in their "Event Horizon" 

Event Horizon is the limit of the Black Hole, beyond that nothing can leave, don't even photons (Light).

This is the life cycle of different stars, the most massive are those that become  Black Holes

Types of Black Holes:

If they are classifieds according to their mass, exist three types of Black Holes:

1. Supermassive Black Hole: They have a mass of millions of solar masses and are at the center of all galaxies.
2. Stellar Black Hole: They are black holes that are part of the life cycle of the stars of a mass equal to 30-70 solar masses (After the supernova a big star loses some of its mass and the remainder is pressed into this type compact star).
3. Micro Black Holes: They are the smallest Black Holes, their diameter is up to 1 mm (millimeter), however they are also very dense.