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 71781HIP 71802HYG 117956HYG 117957HYG 117960HYG 117961HYG 117962HYG 117963HYG 117964HYG 117967HYG 117971HYG 117972HYG 117973HYG 117974HIP 33499HIP 71898HIP 71900HIP 71904HIP 71914HIP 71978HIP 99503HIP 72044HIP 33549HYG 117976HYG 117978HYG 117979HYG 117980HYG 117981HYG 117982HIP 36626HIP 36627HIP 72062HIP 72078HIP 7227HIP 33573HIP 33583HIP 36669HIP 72117HIP 72122HIP 72123HIP 72124HIP 72208HIP 72211HIP 72229HIP 72281HIP 72287HIP 72300HIP 72346

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