Dwarf stars

The dwarf is generally any star of the main sequence of luminosity class V.

We separate them into the following classes:

Red Dwarf – is a small and relatively cold star of the main sequence of the late spectral type K or M. It is the least massive body within which thermonuclear fusion reactions of helium can still take place. The red dwarfs are thus among the coldest, least massive and least luminous stars in the universe. They emit little light, often achieving only 1 / 10,000 of the Sun’s radiant power. Due to the slow combustion of hydrogen, they have an enormously long estimated lifespan, ranging from several tens of billions to trillions of years. These are the most common stars in the Galaxy. One example of this type of star is Proxima Centauri (the nearest star to us, if we don´t count Sun).

Blue Dwarf – is a hypothetical class of stars that will evolve from a red dwarf after consuming most of its hydrogen fuel. While red dwarfs are slowly fused with hydrogen and radiate heat, blue dwarfs probably do not yet exist in space because the universe is not old enough to form.

The brown dwarf is a substantial object that does not emit energy due to thermonuclear reactions like the stars of the main sequence, but has a fully conductive surface and interior. The brown dwarf is formed from a protostar that does not have enough mass to initiate thermonuclear reactions. The first brown dwarf, Gliese 229b, was discovered in 1994. Its luminosity is a million times weaker than that of the Sun. By 2015, more than 2,800 brown dwarfs were known.

The orange dwarf is the star of the main sequence of the spectral type K. Their masses reach 0.5 to 0.9 the mass of the Sun and the surface temperature from 4000 to 5200 degrees Celsius. These stars are interesting from the point of view of extraterrestrial life, because they are stable stars of the main sequence for a very long time, about 15-30 billion years, compared to 10 billion years in the case of the Sun. If planets form in the orbits around them, life would have plenty of time to form and evolve in such conditions. Examples include Alfa Centauri B and Epsilon Indi.

Yellow dwarf- is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.84 to 1.15 solar masses and surface temperature of between 5,300 and 6,000 K. Like other main-sequence stars, a G-type main-sequence star is converting the element hydrogen to helium in its core by means of nuclear fusion. One example of star this type is our Sun. Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton-proton chain (4 hydrogens form 1 helium), converting about 4 million tons of matter to energy. Some of the nearest except sun are 61 Virginis, Mu Arae, Tau Ceti, …

White Dwarf – is an astronomical object that will form after the end of the existence of a star with a small or medium mass. These stars do not have enough mass to ignite the thermonuclear reaction to burn carbon, they become red giants, discard their outer layers, and remain an inert core composed mostly of carbon and oxygen. The white dwarf represents precisely this exposed core of the star.

Black Dwarf – is the remnant of a star the size of the Sun, from which a white dwarf remained and gradually cooled to a body that emits only the radiation of a black body. There is currently no known black dwarf in our universe, because the universe has not existed long enough for one to form.

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