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 74261HIP 33937HIP 33983HIP 74282HIP 74337HIP 74350HIP 74369HIP 74385HIP 74386HYG 118132HYG 118133HIP 37077HIP 37091HIP 7449HIP 74440HIP 74451HIP 74466HIP 74545HIP 74571HIP 74581HIP 74618HIP 74633HIP 74642HIP 55456HIP 74673HIP 74682HIP 74704HIP 74706HIP 74794HIP 74802HIP 74807HIP 74827HIP 74854HIP 37153HIP 7505HIP 92048HIP 92053HIP 92079HIP 92107HIP 9211HIP 92130HIP 92142HIP 94096HIP 92148HIP 92151HIP 94138HIP 94162HIP 34122

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