Red Dwarfs: The Smallest Stars

Red Dwarfs

Red dwarfs are M-type stars, much less massive and luminous than the Sun. Their mass typically ranges from 0.08 to 0.6 M☉, and their surface temperature is between 2,400 and 3,800 K. Their energy is produced by the fusion of hydrogen (nuclear fusion of hydrogen into helium via the proton-proton chain) very slowly, giving them an extremely long lifespan.

Main characteristics:

• Mass: 0.08 to 0.6 M☉
• Radius: 0.1 to 0.6 R☉
• Effective temperature: 2,400 to 3,800 K
• Main sequence lifetime: 100 to 1,000 billion years

Internal structure of a red dwarf:

• Core: hydrogen fusion
• Fully convective zone: convection transports energy throughout the star
• Photosphere: visible surface
• Chromosphere and corona: outer atmospheres, sometimes very active

Stellar Evolution

Red dwarfs evolve very slowly:

1. Main sequence: stable hydrogen fusion over very long periods
2. Final phase: they generally do not become significant red giants and end as small white dwarfs after billions of years

The Most Studied Red Dwarfs

• Sources: NASA – Stellar Data (new window), International Astronomical Union (new window).

• Source: International Astronomical Union – Stellar Classification (new window)