Low mass second phase

Low mass stars  second phase:

During the red giant phase, the hydrogen gas in the outer shell continues to burn and the temperature in the core continues to increase. At 200,000,000 °C the helium atoms in the core fuse to form carbon atoms. The last of the hydrogen gas in the outer shell is blown away to form a ring around the core. This ring is called a planetary nebula.

White Dwarf:

When the last of the helium atoms in the core are fused into carbon atoms, the medium size star begins to die. Gravity causes the last of the star's matter to collapse inward and compact. This is the white dwarf stage. At this stage, the star's matter is extremely dense.  A white dwarf is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. White dwarfs shine with a white hot light, which comes from the emission of stored thermal energy.

White dwarfs comprise roughly 6% of all known stars in the solar neighborhood.

Black Dwarf:

A black dwarf is created when a white dwarf becomes sufficiently cool to no longer emit significant heat or light. Since the time required for a white dwarf to reach this state is calculated to be longer than the current age of the universe of 13.7 billion years, no black dwarfs are expected to exist in the universe yet, and the temperature of the coolest white dwarfs is one observational limit on the age of the universe. 

If black dwarfs were to exist, they would be extremely difficult to detect, since, by definition, they would emit very little radiation. One theory is that they might be detectable through their gravitational influence.