Yellow dwarfs, or G-type main-sequence stars, are common and larger than most stars in the galaxy. The sun is a typical example, with a mass between 80-120% of Earth’s sun. They produce energy through nuclear fusion and remain on the main sequence for about 10 billion years before becoming a red giant and eventually a white dwarf.
A yellow dwarf is a type of main-sequence star, more properly called a G-type main-sequence star. Earth’s sun is a typical example of this type of star. This type of star has a mass between 80 and 120 percent of the mass of Earth’s sun. These stars vary in color from white to light yellow. The sun is actually white, but it looks yellow from the earth’s surface because its light is scattered in the atmosphere.
Although they are called dwarfs, this term is only used in comparison to the colossal size of giant stars. Yellow dwarfs are even larger than the vast majority of stars in the galaxy, most of which are smaller, cooler red or orange dwarfs. The sun has a volume of about 1,412,000,000,000,000,000 cubic kilometers and a mass of about 1,989,100,000,000,000,000,000,000,000,000 kilograms, making it 1,300,000 times larger than Earth and 332,900 times more massive. It is made up of about 75% hydrogen. Most of the rest is helium, plus some other elements, such as oxygen, carbon and iron, in trace amounts.
A yellow dwarf is a main-sequence star, which produces energy by converting hydrogen to helium through nuclear fusion in its core. The outward pressure produced by this energy is balanced by the star’s gravity, creating a state called hydrostatic equilibrium that prevents the star from collapsing or exploding. Every second, the sun fuses about 600,000,000,000 kilograms of hydrogen into helium and converts about 4,000,000 kilograms of mass into energy. Most of this energy is in the form of heat that gradually moves towards the surface of the star, where it is released as electromagnetic radiation, including visible light, and kinetic energy. This produces temperatures of between 5,000 and 6,000° Kelvin at the surface, up to 15,000,000° Kelvin in the core.
A yellow dwarf remains on the main sequence for about ten billion years, slowly getting brighter as it ages. As more and more hydrogen in the star’s core is converted to helium, the core contracts and gets hotter until its energy output overcomes the star’s gravity. At this time, the star begins to expand, leaving the main sequence and becoming a red giant that will eventually evolve into a white dwarf. Yellow dwarfs aren’t massive enough to become supernovae or black holes. The sun is currently about halfway through the main sequence phase of its life.
Yellow dwarf stars are quite common, making up about 7.5% of the stars in the Milky Way galaxy. A yellow dwarf can be lone like the sun or part of a binary or multiple system. Famous yellow dwarfs visible from Earth to the naked eye include Alpha Centauri and Tau Ceti.
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