Dwarf Stars – White Dwarfs and Black Dwarfs

White Dwarfs and Black Dwarfs are the ending points of average or small stars. A star’s life begins in a swirling gas cloud that collapses under gravity, igniting a fiery nuclear fusion. Over eons, it peacefully burns hydrogen in its core. As fuel ends, it swells into a red giant, briefly burning hotter before casting off its outer layers to form a colorful nebula.

The hot, dense core that remains behind is called a White Dwarf. White dwarf stubbornly radiates heat for trillions of years. Eventually, in the far future, it might even cool completely into a faint, theoretical ember known as a Black Dwarf.

White Dwarfs:

White dwarfs, these aren’t typical stars. They’re the leftover cores, the faint echoes of once-vibrant stars like our Sun.

Formation of White Dwarfs:

A white dwarf is born from the dramatic transformation of a low-mass star. As the star ages and exhausts its hydrogen fuel, it expands into a red giant. But unlike its more massive brethren, it doesn’t explode in a supernova. Instead, it peacefully sheds its outer layers, forming a colorful planetary nebula. The remaining core, incredibly hot and dense, becomes the white dwarf.

Size of White Dwarfs:

While stars come in various sizes, white dwarfs are surprisingly compact. White Dwarfs’ typical diameter ranges from about 0.6 to 2.0 times the diameter of Earth (roughly 9,000 to 30,000 kilometers). Following the diameter, the radius of a white dwarf falls within the range of 1,500 to 10,000 kilometers.

Mass of White Dwarfs:

Despite their diminutive size, white dwarfs pack a heavyweight punch. They typically hold a mass similar to our Sun (around 0.8 to 1.4 solar masses). This incredible density is what makes them truly extraordinary.

Volume of White Dwarfs:

Given their small diameter, the volume of a white dwarf is significantly less than that of a star like our Sun. It’s roughly 100,000 to 1 million times smaller than the Sun’s volume.

Circumference of White Dwarfs:

We can calculate the circumference using the diameter (pi * diameter). Due to the range in diameter, the circumference of a white dwarf can vary between roughly 18,000 and 60,000 kilometers.

Composition of White Dwarfs:

Primarily Electron-Degenerate Matter:

Unlike main sequence stars that rely on nuclear fusion for energy, white dwarfs are composed mostly of electron-degenerate matter. This is a state of matter where immense pressure forces electrons to occupy all the available energy levels, preventing further collapse due to the Pauli Exclusion Principle.

Trace Elements:

While electron-degenerate matter dominates, white dwarfs may also contain traces of elements like helium, carbon, or oxygen depending on the star’s original composition.

Internal Structure of White Dwarfs:

Dense Core:

The core of a white dwarf is incredibly hot, reaching millions of degrees Kelvin.

No Fusion:

Due to the degeneracy pressure, nuclear fusion cannot occur in the core.

Supported by Electron Degeneracy Pressure:

The immense weight of the star is counterbalanced by the repulsive force between the tightly packed electrons.

Properties of White Dwarfs:

Imagine a celestial diamond, small, about the size of Earth, yet incredibly dense, harboring the mass of our Sun. That’s a white dwarf! It doesn’t generate new energy through fusion, but residual heat from its stellar past keeps it glowing faintly. White dwarfs are surprisingly numerous, making up roughly 10% of the stars in our Milky Way galaxy.

High Density:

As mentioned earlier, white dwarfs boast densities millions of times higher than that of the Sun.

Faint Luminosity:

They emit a faint glow due to leftover heat from their stellar past, not ongoing nuclear fusion.

Strong Gravity:

Despite their small size, white dwarfs possess immense gravity due to their concentrated mass.

Black Dwarfs:

Over timescales exceeding trillions of years, a white dwarf slowly sheds its heat through radiation. This is where the concept of a black dwarf emerges.

Formation of Black Dwarfs:

White Dwarfs don’t generate new energy through fusion, it still glows faintly due to the leftover heat from its fiery past. Over trillions of years, this heat slowly radiates away, leading to the theoretical concept of a black dwarf.

A black dwarf represents the theoretical endpoint for a white dwarf. It’s a burnt-out ember, a star remnant radiating no visible light and possessing minimal heat. While the existence of black dwarfs hasn’t been directly confirmed due to their faintness, they hold significance for our understanding of stellar evolution.

Due to the theoretical nature of black dwarfs, there are no confirmed observations to provide definitive measurements for their properties. However, we can make some educated guesses based on our understanding of white dwarfs and stellar evolution:

Size of Black Dwarfs:

Black dwarfs are expected to be roughly similar in size to white dwarfs, ranging from an estimated 0.6 to 2.0 times the diameter of Earth (9,000 to 30,000 kilometers).

Mass of Black Dwarfs:

They likely retain a mass similar to white dwarfs, around 0.8 to 1.4 solar masses.

Volume of Black Dwarfs:

Following the size constraints, the volume of a black dwarf would be comparable to a white dwarf – hundreds of thousands to millions of times smaller than the Sun.

Circumference of Black Dwarfs:

Similar to white dwarfs, the circumference would depend on the diameter, potentially falling between 18,000 and 60,000 kilometers.

Composition of Black Dwarfs:

Black dwarfs are theorized to consist primarily of the same electron-degenerate matter that dominates white dwarfs. This is a state of matter where immense pressure forces electrons to occupy all available energy levels, preventing further collapse. Traces of elements like helium, carbon, or oxygen left over from the white dwarf stage might also be present.

Internal Structure of Black Dwarfs:

Much like white dwarfs, black dwarfs are expected to have a dense core, but even colder. Since no nuclear fusion occurs, the internal structure would be determined by the balance between gravity and the repulsive force of the tightly packed electrons.

Properties of Black Dwarfs:

Extremely Faint:

The defining characteristic of a black dwarf is its faintness. The immense cooling over trillions of years would result in them emitting close to no heat or light, making them incredibly difficult to detect.

High Density:

Like white dwarfs, black dwarfs are expected to possess densities millions of times higher than that of the Sun due to the compressed matter.

Low Temperature:

The key difference from white dwarfs is the theorized extremely low temperature, approaching absolute zero.

Difference Between White Dwarfs and Black Dwarfs:

We will discuss the difference between white dwarfs & black dwarfs.

White Dwarfs Vs. Black Dwarfs:

FeatureWhite DwarfBlack Dwarf (Theoretical)
FormationRemaining coreCooled white dwarf
CompositionElectron-degenerate matterLikely similar to white dwarf
TemperatureMillions of degrees KelvinExtremely low
Light EmissionFaint glowNo significant heat or light
Size (Diameter)0.6 – 2.0 Earth diametersSimilar to white dwarf
Mass0.8 – 1.4 solar massesSimilar to white dwarf
ObservableYesNo (currently)


Studying the life cycle of stars, from vibrant suns to faint white dwarfs and black dwarfs, is a humbling journey. It reveals the grand narrative of stellar evolution, a story where even mighty stars eventually fade. By understanding these we gain perspective on our own place in the universe.

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