page_title: Red dwarf
section_title: Definition
hierarchical_section_title: Red dwarf / Definition
caption_attribution_description: English: Shining brightly in this Hubble image is our closest stellar neighbour: Proxima Centauri. Proxima Centauri lies in the constellation of Centaurus (The Centaur), just over four light-years from Earth. Although it looks bright through the eye of Hubble, as you might expect from the nearest star to the Solar System, Proxima Centauri is not visible to the naked eye. Its average luminosity is very low, and it is quite small compared to other stars, at only about an eighth of the mass of the Sun. However, on occasion, its brightness increases. Proxima is what is known as a “flare star”, meaning that convection processes within the star’s body make it prone to random and dramatic changes in brightness. The convection processes not only trigger brilliant bursts of starlight but, combined with other factors, mean that Proxima Centauri is in for a very long life. Astronomers predict that this star will remain middle-aged — or a “main sequence” star in astronomical terms — for another four trillion years, some 300 times the age of the current Universe. These observations were taken using Hubble’s Wide Field and Planetary Camera 2 (WFPC2). Proxima Centauri is actually part of a triple star system — its two companions, Alpha Centauri A and B, lie out of frame. Although by cosmic standards it is a close neighbour, Proxima Centauri remains a point-like object even using Hubble’s eagle-eyed vision, hinting at the vast scale of the Universe around us.Español: El brillante resplandor en esta imagen del Hubble es nuestro vecino estelar más cercano: Próxima Centauri. Proxima Centauri se encuentra en la constelación de Centaurus (El Centauro), poco más de cuatro años-luz de la Tierra. A pesar de que parece brillante por el ojo de Hubble, como se podría esperar de la estrella más cercana al Sistema Solar, Proxima Centauri no es visible a simple vista. Su luminosidad media es muy baja, y es muy pequeña en comparación con otras estrellas, en sólo alrededor de una octava parte de la masa del Sol Sin embargo, en ocasiones, que aumenta su brillo. Proxima es lo que se conoce como una "estrella bengala", lo que significa que los procesos de convección dentro del cuerpo de la estrella hacen propenso a cambios aleatorios y dramáticos en el brillo. Los procesos de convección no sólo desencadenan brillantes estallidos de luz de las estrellas, pero, en combinación con otros factores, hacen que Proxima Centauri posea una vida muy larga. Los astrónomos predicen que esta estrella se mantendrá de mediana edad - o una estrella "secuencia principal" en términos astronómicos - por otros cuatro billones de años, algunos 300 veces la edad del Universo actual. Estas observaciones fueron tomadas con el campo ancho de Hubble y la cámara planetaria 2 (WFPC2). Proxima Centauri es en realidad parte de un sistema estelar triple - sus dos compañeros, Alpha Centauri A y B, se encuentran fuera del marco. Aunque para los estándares cósmicos es un vecino cercano, Proxima Centauri sigue siendo un objeto puntual incluso utilizando la visión ojos de águila del Hubble, haciendo alusión a la gran escala del universo que nos rodea.
context_page_description: A red dwarf is the smallest and coolest kind of star on the main sequence. Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed. From Earth, not one that fits the stricter definitions of a red dwarf is visible to the naked eye. Proxima Centauri, the nearest star to the Sun, is a red dwarf, as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way.
  The coolest red dwarfs near the Sun have a surface temperature of ~2,000 K and the smallest have radii of ~9% that of the Sun, with masses about ~7.5% that of the Sun. These red dwarfs have spectral classes of L0 to L2. There is some overlap with the properties of brown dwarfs, since the most massive brown dwarfs at lower metallicity can be as hot as 3,600 K and have late M spectral types.
  Definitions and usage of the term "red dwarf" vary on how inclusive they are on the hotter and more massive end. One definition is synonymous with stellar M dwarfs, yielding a maximum temperature of 3,900 K and 0.6 M☉.
context_section_description: The term "red dwarf" when used to refer to a star does not have a strict definition.  One of the earliest uses of the term was in 1915, used simply to contrast "red" dwarf stars from hotter "blue" dwarf stars. It became established use, although the definition remained vague. In terms of which spectral types qualify as red dwarfs, different researchers picked different limits, for example K8–M5 or "later than K5".  Dwarf M star, abbreviated dM, was also used, but sometimes it also included stars of spectral type K.
  In modern usage, the definition of a red dwarf still varies.  When explicitly defined, it typically includes late K- and early to mid-M-class stars, but in many cases it is restricted just to M-class stars.  In some cases all K stars are included as red dwarfs, and occasionally even earlier stars.
  The most recent surveys place the coolest true main-sequence stars into spectral types L2 or L3. At the same time, many objects cooler than about M6 or M7 are brown dwarfs, insufficiently massive to sustain hydrogen-1 fusion. This gives a significant overlap in spectral types for red and brown dwarfs. Objects in that spectral range can be difficult to categorize.
caption: Proxima Centauri, the closest star to the Sun at 4.2 ly, is a red dwarf
exif: {"Image ImageDescription": "Shining brightly in this Hubble image is our closest stellar neighbour: Proxima Centauri. Proxima Centauri lies in the constellation of Centaurus (The Centaur), just over four light-years from Earth. Although it looks bright through the eye of Hubble, as you might expect from the nearest star to the Solar System, Proxima Centauri is not visible to the naked eye. Its average luminosity is very low, and it is quite small compared to other stars, at only about an eighth of the mass of the Sun. However, on occasion, its brightness increases. Proxima is what is known as a \u201cflare star\u201d, meaning that convection processes within the star\u2019s body make it prone to random and dramatic changes in brightness. The convection processes not only trigger brilliant bursts of starlight but, combined with other factors, mean that Proxima Centauri is in for a very long life. Astronomers predict that this star will remain middle-aged \u2014 or a \u201cmain sequence\u201d star in astronomical terms \u2014\u00a0for another four trillion years, some 300 times the age of the current Universe. These observations were taken using Hubble\u2019s Wide Field and Planetary Camera 2 (WFPC2). Proxima Centauri is actually part of a triple star system \u2014 its two companions, Alpha Centauri A and B, lie out of frame. Although by cosmic standards it is a close neighbour, Proxima Centauri remains a point-like object even using Hubble\u2019s eagle-eyed vision, hinting at the vast scale of the Universe around us."}