![]() ![]() Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi. Each second, it fuses approximately 600 million tons of hydrogen to helium, converting about 4 million tons of matter to energy. The Sun is the best known example of a G-type main-sequence star. Like other main-sequence stars, a G-type main-sequence star is in the process of converting hydrogen to helium in its core by means of nuclear fusion. Such a star has about 0.8 to 1.2 solar masses and surface temperature of between 5,300 and 6,000 K, Tables VII, VIII. Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri, Tau Ceti, Capella and 51 Pegasi.įreebase Rate this definition: 1.0 / 2 votesĪ G-type main-sequence star, often called a yellow dwarf, or G dwarf star, is a main-sequence star of spectral type G. 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. The Sun, the star in the center of the Solar System to which the Earth is gravitationally bound, is an example of a G-type main-sequence star (G2V type). Like other main-sequence stars, a G-type main-sequence star converts the element hydrogen to helium in its core by means of nuclear fusion, but can also fuse helium when hydrogen runs out. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about 5,300 and 6,000 K. ![]() At the lower-left is the band of white dwarfs - these are the dead cores of old stars which have no internal energy source and over billions of years slowly cool down towards the bottom-right of the diagram.Wikipedia Rate this definition: 0.0 / 0 votesĪ G-type main-sequence star (spectral type: G-V), also often, and imprecisely called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Above them lie the much rarer bright giants, supergiants and hypergiants. Giant stars form their own clump on the upper-right side of the diagram. The ordinary hydrogen-burning stars like the Sun are found in a band running from top-left to bottom-right called the Main Sequence. "This diagram is a plot of 22,000 stars from the Hipparcos Catalogue together with 1000 low-luminosity stars (red and white dwarfs) from the Gliese Catalogue of Nearby Stars. The Sun, for example, is around 15 million degrees at its center. Note that the temperatures quoted are surface temperatures. A plot of luminosity (absolute magnitude) against the color of stars ranging from the high-temperature blue-white stars on the left side of the diagram to the low temperature red stars on the right side. A red dwarf with, perhaps, 10% of the Sun's mass, may spend over a trillion years on the main sequence. On the other hand, small stars last much longer. VY Canis Majoris is perhaps 20 times the size of the Sun, and only a few million years old, but is nearing the end of its days. Really massive stars can use up their Hydrogen in mere millions rather than billions of years. The sun is about half way through a main sequence life of around 10 billion (10 9 ) years. The more massive a star, the faster it burns up its hydrogen, so the shorter its life. The sun is yellow and toward the middle of the range. Cooler stars are redder, while hotter stars are bluer. Brightness (luminosity) and color are functions of the mass of the star. While stars are converting hydrogen into helium in their core they are referred to as main sequence stars. The energy this produces counteracts the force of gravity so the star stops contracting. The Sun, for example, converts about 98.3% of its hydrogen using the proton-proton reaction, the remaining 1.7% via the CNO cycle. In stars heavier than 1.3 solar masses, the CNO cycle dominates. In stars up to about 1.3 solar mass, the proton-proton chain reaction dominates. The high temperature is necessary to give the protons enough energy that they move fast enough that when they collide, their "speed" overcomes the repulsion between them. As hydrogen nuclei are protons, which carry a positive charge, they repel each other. Once the temperature reaches about 10 million K (~ 18 million ☏), nuclear fusion reactions start that convert hydrogen into helium. The time required for the gas cloud to condense into a proto-star is of the order of ten million years. These clouds, containing about 75% hydrogen, collapse and the contraction causes the internal temperature to rise. ![]() Stars form from dense clouds of relatively cool, tenuous gas located primarily in the spiral arms of galaxies. ![]()
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