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Representative lifetimes of stars as a function of their masses The change in size with time of a Sun-like star Artist's depiction of the life cycle of a Sun-like star, starting as a main-sequence star at lower left then expanding through the subgiant and giant phases, until its outer envelope is expelled to form a planetary nebula at upper right Chart of stellar evolution A mass-radius plot ...
These stars are of particular interest in the search for extraterrestrial life due to their stability and long lifespan. These stars stay on the main sequence for up to 70 billion years, a length of time much larger than the time the universe has existed (13.8 billion years), as such none have had sufficient time to leave the main sequence. [2]
The more massive the star, the shorter its lifespan, primarily because massive stars have greater pressure on their cores, causing them to burn hydrogen more rapidly. The most massive stars last an average of a few million years, while stars of minimum mass (red dwarfs) burn their fuel very slowly and can last tens to hundreds of billions of years.
A 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. Such a star has about 0.9 to 1.1 solar masses and an effective temperature between about 5,300 and 6,000 K (5,000 and 5,700 °C ; 9,100 and 10,000 °F ).
The transition in primary energy production from one form to the other spans a range difference of less than a single solar mass. In the Sun, a one solar-mass star, only 1.5% of the energy is generated by the CNO cycle. [32] By contrast, stars with 1.8 M ☉ or above generate almost their entire energy output through the CNO cycle. [33]
An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K. [2] Tables VII and VIII. This temperature range gives the F-type stars a whitish hue when observed by the atmosphere.
A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K . [ 1 ]
These stars are only 5–10 times the radius of the Sun (R ☉), compared to red giants which are up to 300 R ☉. The coolest and least luminous stars referred to as blue giants are on the horizontal branch, intermediate-mass stars that have passed through a red giant phase and are now burning helium in their cores.