Thermal Time Scale

Thermal Time ScaleĀ is the time taken by electromagnetic radiation to reach the surface of the star from the center. In other words, the thermal time scale is the time in which a star would radiate away all its thermal energy if the nuclear energy production were suddenly turned off.

The thermal time scale is estimated using the expression

t_T \simeq \frac{0.5 \times GM^2 / R}{L} = \frac{GM^2}{2R}

For the sun, t_T is estimated as 2 \times 10^7 years. Thus for other stars, thermal time scale can be calculated as,

t_T = \frac{M/M_o}{(L/L_o)(R/R_o)} \times 2 \times 10^7 years

For the sun, the thermal time scale is about 1/500 of the nuclear time scale.

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