赫罗图

光谱型态

棕矮星

白矮星

红矮星

次矮星

主序星

(矮星)

次巨星

巨星

亮巨星

超巨星

特超巨星

绝对

星等

(M_V)

黑矮星是假想中的恒星残骸，是当一颗白矮星的温度低到不再能发出可以被侦测到的光或热的状态。由于一颗白矮星要达到此种状态所需要的时间远高过当前137亿年的宇宙年龄，因此在现今的宇宙中不可能存在着黑矮星，而温度最低的白矮星将会是宇宙年龄的一个观测极限。

白矮星是由主序带上中或低质量的恒星（质量上限在9或10倍太阳质量），在它拥有的温度能使用的元素都在融合中耗尽或驱逐之后的残骸。一个高密度的电子简并物质除了缓慢的热辐射之外，还能留下什么？最终将成为一颗黑矮星。如果真有黑矮星存在，它也很难被侦测到，因为依照定义，它们只有很少的辐射。一种理论认为可以利用重力的扰动来检出。

Hertzsprung–Russell diagram

Spectral type

Brown dwarfs

White dwarfs

Red dwarfs

Subdwarfs

Main sequence
("dwarfs")

Subgiants

Giants

Bright giants

Supergiants

Hypergiants

absolute
magni-
tude
(M_V)

A black dwarf is a theoretical stellar remnant, specifically a white dwarf that has cooled sufficiently that it no longer emits significant heat or light. Because the time required for a white dwarf to reach this state is calculated to be longer than the current age of the universe (13.8 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. A white dwarf is what remains of a main-sequence star of low or medium mass (below approximately 9 to 10 solar masses (M_☉)) after it has either expelled or fused all the elements for which it has sufficient temperature to fuse. What is left is then a dense sphere of electron-degenerate matter that cools slowly by thermal radiation, eventually becoming a black dwarf. If black dwarfs were to exist, they would be extremely difficult to detect, because, by definition, they would emit very little radiation. They would, however, be detectable through their gravitational influence. Various white dwarfs cooled below 3900 K (M0 spectral class) have been found recently by astronomers using MDM Observatory's 2.4-meter telescope. They are estimated to be 11 to 12 billion years old.