For 10 points, name these stellar objects that come in blue, red, brown, and white varieties and are named for their small size.
PG 1159 stars are thought to be the transition phase between planetary nebulae and one class of these objects, which, like neutron stars, cool via the emission of neutrinos in a mechanism known as the Urca process. The inability to sustain hydrogen-1 fusion characterizes a type of these objects known as "failed stars," while electron degeneracy pressure prevents the collapse of another type until it reaches the Chandrasekhar limit. For 10 points, name these stellar objects that come in blue, red, brown, and white varieties and are named for their small size.
PG 1159 stars are thought to be the transition phase between planetary nebulae and one class of these objects, which, like neutron stars, cool via the emission of neutrinos in a mechanism known as the Urca process.
{dwarf stars} [Do not accept any specific types of dwarf stars.]