White Dwarfs: Stars at the End of Their Life

White Dwarfs

White dwarfs are the compact remnants of low- to intermediate-mass stars (< 8 M☉), after they have exhausted their hydrogen and gone through the giant phases. They no longer produce energy through nuclear fusion and radiate their residual heat. These stars typically have a mass of 0.5 to 1.4 M☉ concentrated in a radius comparable to that of Earth (~0.01 R☉), resulting in extremely high densities.

• Mass: 0.5 to 1.4 M☉
• Radius: 0.008 to 0.02 R☉ (~7,000 to 14,000 km)
• Surface temperature: 5,000 to 100,000 K depending on age
• Cooling time: several billion years

Internal Structure

The internal structure of white dwarfs is very different from that of active stars:

• Core: mainly composed of carbon and oxygen (or helium for the lightest)
• Atmosphere: thin outer layer of hydrogen or helium
• Electron degeneracy pressure: prevents gravitational collapse

Stellar Evolution

White dwarfs result from the evolution of stars like the Sun:

1. Main sequence: stable hydrogen fusion
2. Red giant phase: expansion and helium fusion
3. Loss of outer layers: formation of a planetary nebula
4. Formation of the white dwarf: dense, hot star but without nuclear fusion

Examples of Studied White Dwarfs

Sources: NASA – Stellar Data, International Astronomical Union.

Spectral Notation of White Dwarfs

Source: International Astronomical Union – White Dwarf Classification