Main sequence lifetime

The 1-solar-mass star is not capable of producing the heavier nuclei and the majority of the elements in the Periodic Table. With sufficient initial mass of H the He core produces 12C, the point at which the star starts to die. The formation of an almost pure He core results in the end of the star s main-sequence lifetime. The core of the star begins to contract, raising the temperature to 108 K until the nuclear reactions involving He start. 

Spectral type (color) Atmospheric temperature (K) Spectral features M/M R/R L/L Main sequence lifetime... 

Schematic cross-section of a 1.5 M star showing concentrations of various nuclei as a function of depth within the star at the end of its main sequence lifetime. The position within the star is given in units of mass normalized to the solar mass, with zero being the center and 1.5 M being the surface of the star. The outer portion of the star from 1 M to the surface has the initial abundances of the nuclei because this portion of the star was never hot enough for nuclear burning. The region from...

One of the most fascinating aspects of red dwarfs is their longevity. The Main Sequence lifetime of a red dwarf is about a hundred billion years. Since this is older than the age of the Universe (which is 10-15 billion years), red dwarfs have not reached the white dwarf stage. 

Table 5. The p-p chains. The bottom two lines show energy yield per 4He nucleus produced and the relative total yield over the main-sequence lifetime of a solar-type star...

The significance of a convective core is twofold. In the first place, convection mixes proton-rich material from a region much larger than that which is actually burning, thus increasing the total fuel available and extending the potential main-sequence lifetime by a comparable amount. 

Initial mass (M ) Main-sequence lifetime Total stellar lifetime... 

Stars on the upper left of the Main Sequence are massive dwarfs. Stars on the lower right of the Main Sequence are light dwarfs (see figures 5.1 and 5.3). Recall that at the end of chapter 4, we discussed how stellar lifetime is inversely proportional to the mass of a star or more specifically, x (1/M)2-5. A rare O-... 

As the star approaches the Main Sequence, it enters one of the most dramatic periods of its lifetime, the T-Tauri stage. The name T-Tauri comes from the first star observed that exhibited the events associated with this stage of stellar evolution. T-Tauri stars eject large proportions of their mass in violent bursts. 

The index MS denotes lifetime on the main sequence. This formula yields tms = 1 X 10 yr for stars with one solar mass. For the very hot and bright massive 05 stars for example the lifetime is only 8x10 years. For the faint less massive MO stars for example the expected lifetime is 7.9 x 10 years which is a factor of five of the age of the universe. 

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