Last updated: August 29, 2025

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 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:

Main sequence: stable hydrogen fusion over very long periods
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

Characteristics of Studied Red Dwarfs
Star	Spectral Type	Mass (M☉)	Radius (R☉)	Temperature (K)	Remarks
Proxima Centauri	M5.5V	0.12	0.14	3,050	Closest star to the Sun
Barnard's Star	M4V	0.16	0.20	3,100	Well-studied low-mass star
TRAPPIST-1	M8V	0.089	0.12	2,550	Famous compact planetary system with exoplanets
Luyten's Star	M3.5V	0.26	0.35	3,450	Nearby star with detected planets
Wolf 359	M6V	0.09	0.12	2,800	Very faint and close to the Sun
Gliese 581	M3V	0.31	0.29	3,200	Famous for its potentially habitable exoplanets
YZ Ceti	M4.5V	0.13	0.16	3,100	Nearby star with a compact planetary system
GJ 667 C	M1.5V	0.31	0.42	3,700	Part of a triple system, several detected planets
Ross 128	M4V	0.17	0.20	3,180	Nearby and relatively calm, exoplanet in the habitable zone
CHXR 73	M3.25V	0.32	0.35	3,490	Young star in the Chamaeleon constellation, age ~2 million years

Sources: NASA – Stellar Data, International Astronomical Union.

Understanding the M5V Notation (Red Dwarfs)
Notation Element	Example	Meaning	Physical Details
Main letter	M	Spectral type	Very cool red stars, temperature 2,400–3,800 K
Number	5	Spectral subtype	0 = hotter, 9 = cooler. M5 is intermediate
Roman letter	V	Luminosity class	V = main sequence dwarf, stable hydrogen fusion