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 83366 HIP 8338 HIP 83394 HIP 83405 HIP 83416 HIP 83430 HIP 8344 HIP 83450 HIP 83455 HIP 83516 HIP 83518 HIP 83519 HIP 83556 HIP 83557 HIP 83582 HIP 83584 HIP 83599 HIP 83618 HIP 83632 HIP 83638 HIP 83713 HIP 83714 HIP 83727 HIP 83762 HIP 8382 HIP 83866 HIP 83868 HIP 83892 HIP 83933 HIP 83935 HIP 83941 HIP 83945 HIP 84004 HIP 84016 HIP 84018 HIP 84027 HIP 84042 HIP 84071 HIP 84105 HIP 84141 HIP 84148 HIP 84165 HIP 84191 HIP 84213 HIP 84223 HIP 84258 HIP 84265 HIP 84277

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

Class M — M-type (Red)

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Characteristics

Notable Examples

Frequently Asked Questions