Class M — M-type (Red)

M-type stars, commonly called red dwarfs, are the coolest and most common main-sequence stars, with surface temperatures of 2,400 to 3,700 K. They make up about 76% of all main-sequence stars, yet none are visible to the naked eye from Earth due to their low luminosity. Proxima Centauri (M5.5Ve), the closest star to the Sun, is an M-type star. Red dwarfs have extremely long lifetimes — trillions of years — far exceeding the current age of the universe. Many host exoplanets, including Proxima Centauri b and the TRAPPIST-1 system.

M-type stars are the coolest, smallest, and by far the most abundant stars in the universe. With surface temperatures below 3,700 K and masses from 0.08 to 0.45 solar masses, red dwarfs constitute approximately 76% of all main-sequence stars — yet not a single one is visible to the naked eye from Earth, despite Proxima Centauri (M5.5Ve) being the nearest star beyond the Sun at just 4.24 light-years. Their extreme longevity (trillions of years) means no M dwarf has ever died of old age in the history of the universe.

Characteristics

M-type spectra are dominated by titanium oxide (TiO) molecular absorption bands, which create their characteristic deep red color. M dwarfs are fully convective below about 0.35 solar masses — meaning they mix their entire hydrogen supply, greatly extending their lifetimes. However, this convection drives powerful magnetic fields that produce frequent, intense flares — some M dwarfs can brighten by factors of 100 in minutes. Their habitable zones lie very close to the star, meaning potentially habitable planets are likely tidally locked. The M class also includes red giants and supergiants — evolved massive stars like Betelgeuse (M1-M2Ia-Iab).

Notable Examples

Proxima Centauri (M5.5Ve) hosts Proxima b, an Earth-mass planet in the habitable zone of our nearest stellar neighbor. TRAPPIST-1 (M8V) has seven Earth-sized planets, three in the habitable zone — the most Earth-like system known. Barnard's Star (M4Ve) is the fastest-moving star in Earth's sky and a target of exoplanet searches since the 1960s. Betelgeuse (Alpha Orionis, M1-M2Ia-Iab) is an M-type red supergiant whose Great Dimming event in 2019-2020 captivated global attention — it will eventually explode as a supernova visible in daylight.

HIP 38634HIP 36334HIP 36347HIP 36349HIP 89621HIP 89669HIP 8968HIP 91699HIP 91703HIP 9171HIP 8051HIP 91855HIP 36495HIP 80523HIP 80529HIP 96998HIP 97170HIP 97235HIP 99150HIP 90115HIP 99983HIP 9999HYG 118370HIP 71802HIP 33499HIP 71900HIP 71904HIP 71914HIP 71978HIP 33549HYG 117978HIP 7227HIP 36669HIP 72122HIP 72123HIP 72124HIP 72346HIP 72406HIP 33592HIP 33600HYG 117995HYG 118000HYG 117984HYG 117990HIP 97693HIP 72509HIP 72511HIP 90254

Frequently Asked Questions

What is a class M star?
Class M (M-type (Red)) stars are red stars. M-type stars, commonly called red dwarfs, are the coolest and most common main-sequence stars, with surface temperatures of 2,400 to 3,700 K. They make up about 76% of all main-sequence stars, yet non
How hot are class M stars?
Class M stars have surface temperatures between 2,400 K and 3,700 K.
What color are class M stars?
Class M stars appear red.
How many class M stars are in the StarFYI database?
StarFYI currently catalogs 5,834 class M stars.
How luminous are class M stars?
Very dim, less than 0.08 solar luminosities