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 89669HIP 8968HIP 8972HIP 91699HIP 91703HIP 9171HIP 8976HIP 91728HIP 8051HIP 91789HIP 91813HIP 89858HIP 89886HIP 89887HIP 91871HIP 36495HIP 80523HIP 80529HIP 89980HIP 89981HIP 96998HIP 98890HIP 90085HIP 901HIP 99150HIP 90115HIP 99983HIP 9999HYG 118370HIP 33453HIP 71665HIP 7208HIP 9767HIP 71749HIP 71802HYG 117956HYG 117957HYG 117960HYG 117961HYG 117962HYG 117963HYG 117964HYG 117967HIP 71978HIP 99503HIP 72044HIP 33549HYG 117978

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